Note: Descriptions are shown in the official language in which they were submitted.
~5~511
This ap~lication is a divlsion of our ~anadian Patent Application
~erial N~ber 337,887 filed October 18~ 19790
~his invention relates to a new and improved micro lens array and
micro deflector sub-assembly abricate~ from silicon selniconductor plates pro-
cessed in accordance with semiconductor microcircuit fabrication technology,
metalizecl in part and held together in assembled relationship by glass rodding
to which the silicon plates are thermally bonded or otherwise secured either
directl~ or through the medium of suitable metal moulding rings. This division-
al application relates in particular to a method of fabricating micro lens arrayplates.
Prior Art Problem
. _
The desirabi.lity of using a ~atrix of micro-electron optical elements
arranged in the manner of a flyls eye lens is a now well-established fact in
that such an arrangement provides large field coverage without sacrifice of
resolution, large beam current, deflection sensitivity of accuracy and other
desirable attributes as described in a paper entitled "Electron Beam Memories"
by DoE~ Speliotis, D.O~ Smith, KoJ~ Ilarte and FoO~ Arntz, presented at the
ELECTRO/76 held at Boston, Massachusetts on ll-l~ May, 1976 and in an article
entitled "Advances in Fly's Eye Electron Optics" appearing in the Proceedings
2Q of the National Electronics Conference, ~ol. ~3, pages 746-751 ~1~67) by S.P.
Ne~Yberry et al. While the desirable characteristics of the fly's eye electron
optical system are well established, as the requirements for the number of chan-nels in the matrix increases and the linear dimensions of the matrix corres-
pondingly decrease in efforts to increase its storage capacity and minimize the
size~ complexity and weight of the equipment, the problems of fabricati~ of
~l~'s eye electron beam systems using known materials and fabrication tec}miquesbecome increasingly difficult if not insurmountableO
In the known prior art fly's eye electron optics system heretofore
t l5 7~1 1
available to the art as described in the above-noted National Electronics
Conf. article, the micro lens array sub-assembly has been fabricated in the
form of a "top hat" structure as shown in Pigure 2 of the article. In this
form of micro lens array, the focusing element of the micro lens consists of
an array of holcs formed in thin metal plates. The thin metal plates in turn
are tightly stretclled and bonded to a strong mctal ring and the holes are
produces by a variety of methods sucll as drilling~ punching and photo-chemical
etching to mention a few~ The problems encountered with these known micro
lens array structures are:
~1) Photo-chemical etching of metal is expensive and does not result
in lens aperture openings having required roundness, smoothness and
~miformity between holes in the array.
(2) While punching of holes does reduce cost substantially, ancl if
followed by a finishing operation such as shaving, does produce
uniform diameters and smooth surfaces~ these procedures cannot be
accomplished on a matrix of holes ~lens aperture openings) in which
the hole diameter equals or even approaches the optimum ratio to the
spacing between holes.
(3) The use of heavy metal rings to support the thin plates does not
permit close spacing of the plates as the spacing between lens
aperture openings (channels) is decreased to optimize density of
channels and minimize size. If the "top hat" structure shown in Figure
2 of the National ~lectronics Conference article is employed, while
permitting close spacing between lens plates, it is expensive and uses
space inefficiently, but most seriously, it prevents close approach to
one side of the lens elements by neighboring elements of the overall
11~7511
fly's cye electron optical system.
~4) If an attempt is made to avoid the above-discussed difficulties
encountered with the use of thick mounting rings or the "top hat"
configuration by using metal plates which are thick enough to be
self-supporting, eventually the impossible condition would be reached
in largc arrays ~e.g., arrays having lens elements numbering 128 x
128) where the plate thickness required for mechanical rigidity
exceeds the spacing between the plates required for optimum electron
optical performance. Additionally, thick plates are more costly to
process in the fabrication of the lens aperture openings ~holesj, are
more severelylimited in hole size permitted, and are inclined to
warp during bake-out temperature cycling due to built-in strains.
Finally, as with thin metals, the desired op~imum hole diameter to
spacing between holes cannot be achieved.
Turning attention now to the micro deflector structure for achieving
fine deflection, the above-mentioned National Electronics Conference article
describes a micro deflector construction which has been successfully applied
to the fly's eye lens and comprises two sets of parallel conductive bars in
tandem. The use of metal plates to produce the deflection bars has not been
satisfactory7 however, for reasons to be discussed hereafter. Sawing of bars
from ceramic blocks and metalization of the ceramic bars, has produced electron
optically acceptable fine deflectors but the cost has been unacccptable and the
yield very low. In summary, experience with the known fine deflector sub-
assembly design has taught the following lessons:
(1~ Micro deflector systems which depend upon production of individ-
ual deflector plates which are subsequently stacked together with
--3--
~157Sl:~
spacers re~uirc unreasonable tolerance control because the position
error is cumulative. Single blade metal deflectors are better than
metal deflectors sawed from solid stock J but they arc expensive and
too thin to remain straight unless placed in tension by the assembly.
(2) Thin metal plates are microphonic at some resonant frecluency
and this resonance can be excited by ~he application of periodic
changes in -the deflection voltage such as a raster scan.
(3) In micro deflector systems which use deflector bars sawed from
blocks, the ceramic blocks must be sawed in the fired state ~i.e.,
very hard) in which state they are so abrasive that even diamond
tools wear rapidly and the dimensions are very difficult to hold.
Thus, they are costly to produce.
In addition to the component fabrication problems discussed above,
the overall structure, i.e., the micro lens array plus micro deflector and
target electrode member, has further constraints. Since a single piece of
dirt can spoil an assembly for many applications, the assembled structure must
either be capable of disassembly for cleaning or fabricated by techniques
which leave it electron optically clean. Additionally, the assembly must not
permit relative mo~ion of the parts by environmental factors such as
vibration or thermal excursions. Two of the most important applications for
fly's eye type electron beam tubes are in electron beam accessed semiconductor
target memories for use with computers and in microcircuit pattern fabrication.
In these applications, if the target area covered is large, then temperature
excursions pose a severe problem with the mixing of construction materials
such as metals, ceramics and semiconductor targets each with a different
temperature coefficient of expansion and pattern displacement of several
--4--
. 11$7511
microns can occur clue to normal room temperature vari.ltions. Thus, it will be
appreciated that the above-listed requirements can make the overall assembly of
a fly's eye electron beam tube micro lens array and micro deflector a very
difficult problem.
From the Eoregoing discussion~ it will be appreciatcd that new materials
and methods of construction of micro lens arrays and micro deflector sub-
assemblies are required if the benefit of higher density, larger arrays are to
be achieved for the industry.
SU~ARY OF T~IE INVENTION
It is a primary object of the present invention to provide a new and
improved micro deflector sub-assembly for use in electron beam tubes of the
fly's eye type and which is fabricated from silicon, either in single crystal
or polycrystalline form, to the greatest extent possible and ~herein certain
parts are processed in accordance with silicon semiconductor microcircuit
fabrication techniques and other parts of which are metallized and the various
parts held together in an assembled structure by glass rodding. The advantages
obtained by fabricating the fly's eye electron optical assembly from silicon
in this manner are:
~ (1) In electron beam accessed memories, thermal match is obtained
between the recording media and the micro lens array and micro deflector
elements since such elements are formed of silicon and glass rodding
which has a temperature coefficient of expansion very near to that of
silicon.
(2) The high purity and regularity of the material ~single crystal
silicon) permits construction of the micro lens elements by known
microcircuit photo-etch techniques and better quality holes and
I ~ ~ 7~ ~ 1
straighte-r cclges are obtained in comparison to holes formed in metals
or an~orpllous materials.
(3) ~cwer problems are encountered with the fla-tness of the materials.
(4) It is not necessary to mount the micro lens plates on a supporting
ring of sllbstantial thickness thercby permittin~ closer spacing between
the micro lens plates.
(5) As will be explained more fully hereafter, it is possihle by
appropriate fabrication techniques to make bi-layer lens elements
without bimetallic thermal effects thus permittîng the construction
of highly conductive, buttressed outer lens plates having ultra thin
lens aperture openings formed on a silicon lens plate of substantial
thickness and conductive layers on each of the opposite sides thereof.
~6) Metalization (if needed) and bonding techniques for silicon plates
are well established and proven.
~7) Extr~me cleanliness and stability at bake-out can be obta-ined for
the resulting structure.
(8) Polycrystalline siiicon is easier to saw and metalize than ceramic
thus making the problem of micro deflector bar fabrication much less
costly and better controlled.
(9) In addition to producing smoother more uniform lens aperture
openings (holes) in silicon plates, the photochemical etching techniques
used in producing the holes permit hole size to center spacing to be
controlled to optimum values.
In practicing the invention a combined fine focusing micro lens array
and micro deflector sub-assembly is pro~ided for use in electron beam tubes of
the fly's eye type. The assembly comprises a fine focusing micro lens array
~157Sll
sub-assembly formed by a plurality oE spaced-apart, stacked, parallel7 thin,
planar, apertured lens plates each fabricated from silicon semiconductor
material and having an array of micro lcns aperture openings formed therein
by photolithograpilic semiconductor microcircllit fabrication techniques. The
apertured silicon lens plates each have highly conductive surfaces and are
secured to glass rods for holding the plates in stacked, parallel, spaced-
apart relationship with the longitudinal axes of the glass support rods
extending at right angles to the planes of the silicon plates. The apertures
in all of the silicon lens plates are axially aligned in parallel with a
longitudinal axis passing through the center of the array to form an array of
fine focusing lens elements. The assembly further includes a micro dcflector
sub-assembly mountcd immediately adjacent to the fine focusing micro lens
array and defining a honeycomb matrix of sets of orthogonally disposed micro
deflector elements, there being a set of orthogonally disposed micro deflector
elements axially aligned with each respective fine focusi~g lens element
formed by the axially aligned aperture openings of the stacked parallel spaced-
apart silicon lens plates for deflecting an electron beam passing through a
respective axially aligned fine focusing micro lens array element along orth-
ogonal x-y directional axes of movement in the plane normal to the electron
beam path. The honeycomb matrix of sets of micro deflector elements are
comprised by two orthogonally arrayed sets of parallel, spaced-apart deflector
bars which define the respective orthogonally arrayed sets of micro deflector
elements with alternate bars of each set of deflector bars being interconnected
electrically for common connection to a respective source of fine x-y deflection
potential. In one preferred embodiment, the thin planar apertured lens plates
comprise a thin planar wafer of single crystalline silicon about 2 microns thick
1 1~7~ 1 1
and having a matrix o~ lens aperture openings formed therein by etching from
one side only all -the way th~ough the thickness of the wafer~ ~n a second pre-
ferred embodiment, the thin planar apertured lens elements each comprise a thin
planar single silicon wafer of about 1/2 millimeter in thickness etched from
each o the opposite planar sides thereof through openings defined by a masking
area formed on both planar surfaces of the Nafer where no openings are to formed
and application of a suitable etchant to both sides of the wa~er.
According to one broad aspect of the invention there is provided a
method of fabricating micro lens array plates from round, thin planar single
crystalline silicon semiconductor wafers of about 1/2 millimeter thickness or
less comprising the steps of: (a) growing a wet silicon dioxide layer on both
flat planar surfaces of the silicon ~Yafer to a thickness of several hundred
Ang~trom units; ~b) by photoli~hographic techniques employing a photo-resist and
solvent for silicon dioxide form an array of silicon dioxide dots on both sur-
faces of the silicon wafer where it is desired that aperture openings be formed
~ith the centers of each set of opposing silicon dioxide dots on the opposite
surfaces of the silicon ~afer being axially aligned on a common axis passing
through both centers and perpendicular to the plane of the wafer; (c) spin coat
a boron containing emulsion over both silicon dioxide dotted flat surfaces o
2Q the wafer and fire wafer in a nitrogen atmospher0 at substantially 1100C, to
thereby grow a heavily boron doped layer of about 2 microns thickness in sur-
~ace areas of wafer where it is desired that no aperture openings be formed;
Cd) remove excess boron containing emulsion in a hydro-fluoride bath and remove
~ilicon dioxide dots in a fresh hydro-fluoride bath to leave a deep heavily boron
doped and highl~ conductive layer of about 2 microns thickness in those planar
surface areas on both sides of the wafer ~here it is desired that no apertures
l 1 ~75 1 :1
be for~ed interspersed with an array of dotted ~mdoped silicon surface areas
here it is desirecL that apertures be formed; ~e) etching the wafer in an
etchant co~prising a hot pyrocatechol and ethylene diamine bath which attacks
the dotted undoped silicon surface areas of the wafer previously protected by
the silicon dioxide dots during the boron doping step at a faster differentlal
rate than it attacks the boron doped surface areas; and ~f) continuing the etch-
ing until an array o lens aperture openings of a desired diameter have been
formed all the way through the thickness o the wafer by the meeting o the
5imultaneously etched pockets produced on both sides of the ~afer by the diff-
erential etching action of the etchant on the dotted undoped silicon surfacearea~.
According to ano~her broad aspect of the invention there is provided
a ~ethod of fabricating Inicro lens array plates from round, thin planar single
crystalline silicon semiconductor wafers of about 1/2 millimeter thickness com-
prising the steps of: ~a) growing a wet silicon dioxide layer on one flat
planar surface to a thickness of several hundred ~Igstrom units, ~b) by photo-
lithographic techniques employing a photo resist and solvent for silicon dio-
xide produce an array of silicon dioxide dots where it is desired that aperture
Qpenings be formed on one side only of the wafer; ~c) by photolithographic
2Q techniques employin~ a photo resist and solvent for silicon dioxide produce an
enlarged area of unmasked silicon on the backside of the wafer corresponding to
the area of desired aperture openings on the first mentioned side while leaving
a subs~antial peripheral area of s.ilicon dioxide masked silicon around the
~eripheral edges of the wafer; ~d) spin coat a boron containing emulsion over
silicon dioxide masked surfaces of both sides of the wafer and fire the wafer in
a nitxogen atmosphere at about 1100Co to thereb~ gro~ a heavily boron doped
11S7511
layer of about ~ mîcrons thickness throu~h those surface areas of the wafer
where it is desired that no aperture open.ings be formed; (e) remove excess boron
containing emulsion in a hydrofluoric bath and remove sillcon dio.~ide mask in
a tresh hydrofluoric bath to leave a deep heavily doped and highly conductive
layer of about 2 mic~ons tllickness in those planar surface areas of the wafer
where it is desired that no apertures be formed interspersed wlth an array of
dotted undcped silicon surface areas where it is desired that apertures be
formed; ~f~ etching the wafer in an etchant comprising a hot pyrocatechol and
ethylene diamine bath which attacks the undoped silicon surface areas of the
1~ wafer previously protected by the silicon di.oxide dots during the boron doping
step at a faster differential rate than it attacks the boron doped surface
areasi and Cg) continuing the etching action until an array of lens aperture
openings of a desired diameter have been formed all the way through the thick-
ness of the wafer by the differential etching action of the etchant on the
dotted undoped silicon surface areas while leaving a substantial peripheral
portion of the original starting wafer thickness to provide rigidity to the
resultant lens plateO
In preferred embodiments, the deflector bars of the micro deflector
sub-assembly are fabricated from polycrystalline silicon having metalized sur-
faces. The two orthogonally arrayed sets of parallel, spaced-apart deflection
~ars are held in assembled spaced-apart, parallel relationship by respective
sets of supporting glass rods whose longitudinal axes extend in a
~ 8b _
t 1 $~75 1 ~
plane par~llel to the plane of the deflector bars but at right angles thereto
and to which thc ends of the deflector bars are fused.
In one preferred embodiment, the micro lens array sub-assembly and the
micro deflector sub-assembly have the glass suppor-t rods thereof thermally
bonded to respective, annularly shaped outer support rings comprised of
molybdenum, tungsten or other suitable metal and having alignment notches
formed around the periphery thereof for facilitating alignment of the respective
sub-assemblies. The outer support rings in turn then are thermally bonded to
an additonnal set of glass support rods whose longitudinal axis extend at
right angles to the planes of the apertured silicon plates and to the plane of
the deflector bars for holding the two sub~assemblies in assembled relationship.
In another preferred embodiment, the thin apertured silicon lens plates
are thermally bonded directly to a set of glass support rods whose longitudinal
axis extends at right angles to the planes of the lens plates and to which the
support rods for the micro deflector bars also are thermally bonded.
The micro deflector sub-assembly further comprises end deflector bars
which have extensions of malleable metal material extending beyond the points
of connection of the ends of the end deflector bars for use as mounting tabs
either to the outer support ring, or directly to the glass support rods which
extend at right angles to the plane of the micro deflector bars. In structures
which do not employ the outer support rings having alignment notches,
alignment of the micro deflector elements is obtained by light optical or
electron optical alignment techni~ues and usion of the various silicon elements
to the glass support rods can be obtained by electron beam heating or laser
beam heating and fusion jointure. In assemblies where bonding rings are not
employed, the set of glass support rods to which both the micro lens array and
~15'7511
the micro deflector sub-assemblies are secured, have the ends thereof shaped
to seat with and be fused to a precision insulating sapphire ball that is in
turn seated in and fused to a socket formed in an annularly shaped supporting
ring for mounting the assembly within the housing of a -flyls eye type electron
beam tube. The structure thus comprisecl also has a target electrode member
fabricated from silicon semiconductor material mounted in parallel to the
micro lens array and micro deflector bar but spaced therefrom and secured by
fusion to the common glass support rods~
1ectrical connection to at least one of the thin apertured silicon
lens plates of the micro lens array sub-assembly is obtained by trapping an
exposed portion of a conductive wire between the hot glass of at least one of
the glass sùpport rods and the conductive surface of the respective plate during
thermal bonding or fusion of the plates to the glass support rods. The
conductive wire thereafter may be connected by conventional lead-in insulated
conductor to a source of electric energy.
In anothcr preferred embodiment, the glass support rods at the point o~
thermal bonding to the silicon lens plates have projections formed thereon
extending inwardly to con$act the peripheral edge portions of the silicon
plates at the point of fusion to thereby provide greater effective insulator
distance between adjacent silicon plates while maintaining minimum physical
spacing or plate separation distance between the plates. If desired, the lens
aperture openings formed in at least one of the thin apertured silicon lens
plates need not be round but may be semi-elliptical or of another configuration
for reducing third order aberrations.
In-embodiments wherein because of the intended application it may be
necessary to disassemble the assembly from time to time, ring-shaped metal pads
-10-
t l575~ 1
of compatible conductive material are brazed or otherwise secured to points
around the peripheral edge oE the thin silicon apertured lens plates for
increasing the thic~ness thereof and a plurality of insulating ball spaces are
seated in the ring-sllaped metal pads for assembl;ng the thin silicon plates
in a stacked, spaced-apart~ parallel array upon being clamped together in a
self-supportillg structure. Alternatively, a plurality of support holes may
be formed around the peripheral edge portion o at least one of the thin
silicon apertured lens plates and a plurality of small insulating ball spacers
seated in and fused to the holes or providing an insulating mounting means
for the respective thin silicon lens plates and insulating balls.
The combined micro lens array and micro deflector assembly thus
comprised may be uscd with a planar target electrode member of silicon
semiconductor material for an electron beam accessed memory, mounted in
common with the assembly in a vacuum-tight housing or alternatively may be used
with a target member of electron sensitive material ~such as a photosensitive
target or an electron etchable photo resist target member used in the fabrica-
tion of microcircuits) removably mounted by a vacuum-tight enclosure in
common with an in a plane parallel to the thin apertured micro lens silicon
plates and the plane of the micro deflector bars. With either type of
application, the assembly may be used with a coarse deflector electrode system
or alternatively with a graded field electrode system located intermediate
the electron gun of the electron beam tube and the fly 15 eye electron optical
system thereby allo~ing the new and improved fly's eye electron optical
system to be used either with a coarse deflected beam of electrons~ or a
uniform flood of electrons.
1 1~751 1
BRIEF DESCRII'TION OF Tll D~\WINGS
These and other objec*s, features and attendant advantages oE the
invention will become better understood after a reading of the following
detailed description considered in connec~ion with the accompanying drawings
wherein like parts in each of the several figures are identified with the
same reference number, and wherein:
Figure 1 is a longitudinal sectional view of a new and improved micro
lens array and micro deflector assembly for fly's eye electron beam tubes
using silicon micro lens elements and micro deflector plates and constructed
according to the invention;
Figure 2 is an end view of the micro lens array and micro deflector
assembly shown in Figure l looking through the entrance end thereof relative
to an electron beam passing through the assembly, with the longitudinal
sectional view shown in Figure 1 being ta~en through plane 1-1 of Figure 2;
, Figure 3 is a longitudinal sectional view of a micro lens array sub-
assembly constructed according to the invention and comprising a part of the
assembly shown in Figure l;
Figure 4 is an end view of the micro lens array sub-assembly shown in
Figure 3;
Figure 5 is an end view of the micro deflector sub-assembly comprising
a part of the overall assembly shown in Figures 1 and 2;
Figure 6 is a longitudinal sectional view of the micro deflector sub-
assembly shown in Figure 5 and ta~en through plane 6-6 of Figure 5;
Figure 7, on the second sheet of drawings, is a sectional view of a
- target electrode sub-assembly comprising apart of the assembly shown in Figu-
res 1 and 2;
-12-
115751 l
Figure ~ is a longitudinal sectional vicw showing a plurali.ty of
annularly-shapcd support rings and the manner of mounting the support rings to
axially extending glass support rods, the support rings being usecl to mount
the micro lens array sub-assembly the micro deflector sub-assembly and a
target electrode member in juxtaposed asscmbled relation :Eor securement within
the evacuated housing of a fly's eye type electron beam tube;
Figure 9 is a longitudinal sectional view of a fly's eye electron beam
tube showing the novel micro lens array and micro deflector assembly constructed
in accordance to the invention used in conjunction with an electron sensitive
target member which may be either photosensitive or may comprise a target
member having an electron sensitive photo resist or other type of surface that
can be selectively etched by an electron beam in the fabrication of semiconduct-
or integrated microcircuits and the like~ and where the fly's eye electron
beam tube is of the type employing a coarse deflector structure for selectively
supplying an electron beam tube through selected ones of the ~icro lens and
micro deflector elements sequentially;
Figure 10 illustrates a variation of the fly's eye type electron beam
tube structure shown in Figure 9 wherein a graded field coarse deflector system
is employed whereby a uniform flood of electrons is supplied at the entrance
end of the micro lens array and micro deflector assembly for use in the
fabrication of micro circuit structures or the like employing electron sensit-
ive target members;
Figure 11 is a longitudinal sectional view of another embodiment of the
invention employing silicon micro lens plates and thin metal deflector bars
mounted on glass support rods in individual sub-assemblies with each sub-assem-
bly being mechanically held together by annularly-shaped metallic support rings;
-13-
~15'7~11
Figure 12 is an end view o.E the alternative micro lens array and
micro deflector assembly shown in Figure 11;
Figure 13 is a longitudinal side view of the micro lens array sub-
assembly only comprising a part of the assembly shown in Figures 11 and 12;
Figure 14 is an end plan view of the micro lens array sub-assembly
sho~Yn in rigure 13 as vie~ed from the electron beam entrance side thereof;
Figure 15 is an end plan view of the micro deflector sub-assembly
only used in the assembly shown in Figures 11 and 12;
Figure 16 is a longitudinal side view shown par~ly in section of
the micro deflector sub-assembly shown in Figure 15;
Figure 17, on the seventh sheet of drawings, is a series of cross-
sectional views taken through a typical set of aligned lens aperture elements
such as the micro lens array sub-assemblies shown either in Pigures 3 and 4 or
Figures 13 and 14 illustrating details of the construction thereof;
Figures 18A-18J illustrate a series of planar end views coupled with
cross-sectional views of a starting single crystalline silicon wafer and shows
the processing of the wafer required in the production of the apertured micro
silicon lens plates employed in the micro lens array sub-assembly used in the
embodiments of the invention shown in Figures 1-10 as well as the embodiment of
the invention shown in Figures 11-17;
Figure 19 is a partial cross-sectional view illustrating the manner of
securement of a thin silicon plate micro lens array element to a supporting glass
rod and in addition illustrates the manner in which a thin, preferably flat,
conductive wire is trapped between the ends of the conductive surface of the thin
flat silicon plate and the glass support rod to which it is thermally bonded,
whereby a desired electric excitation potential may be applied to the silicon
-14-
1157~1
plate, and ~igure 19A illustrates an alternative form of glass rod support made
up of a stack of of~-set type glass washer elements ancl wherein a thin metallic
washer and intcrconnccted lead-in conductor can be employed to apply desired
electric e~citation potentials to the thin silicon plate trapped between the
glass support waslle-r elements.
Figures 20 and 20A-2~F, on the tenth and eleventh sheets of drawings,
illustrate a series of fabrication steps starting wi~h an essentially flat box-
shaped blocX of silicon for constructing the preferred form of micro deflector
sub-assembly according to the invention;
Figures 21 and 21A, on the tenth sheet of drawings, are schematic
illustrations of a preferred form of micro lens array and micro deflector sub-
assembly employing all silicon lens plates, deflector bars and target member
and using only glass support rods without requiring metal mounting rings as a
part of the electron optical assembly;
Figures 22 and 22A show alternative forms of construction for the
glass support rods whereby the length of insulator between adjacent plates of
the micro lens array can be considerably increased without requiring that the
spacing distance between the plates be increased;
Figures 23 and 23A, on the tenth sheet of drawings, show a preferred
assembly technique and construction ~or the metalized silicon bars or blades
of the micro deflector sub-assembly which does not require the use of metal end
deflector bars;
Figures 24 and 24A illustrate the manner in which an all glass and
silicon micro lens array and micro deflector assembly SlJCh as shown in ~igure 21
can be assembled together for securement within the evacuated housing of a fly's
eye electron beam tube, the assembly being achieved with insulating sapphire
1 1575 l I
balls which are heat pressed and thermally bonded to the ends of the glass
support rods in the manner depicted in Figure 24A and seated in holes formed in
suitable support rings;
Figure 25 is a schematic illustration of a preferred technique for
mounting a metal supporting ring in the form of a collar, shrink fi~ted band or
housekeeper's seal around the periphery of a coarse deflector cone for use in
supporting array assemblies according to the invention on such cones;
Figures 26, 26~ and 26B are schematic illustrations of alternative
techniques of assembly for securing all glass and silicon micro lens array and
micro deflector assemblies constructed according to the inventîon together for
mounting within the evacuated housing of a fly's eye electron beam tube whereby
the resultant assembly may be subsequently readily disassembled without
requiring breakage of parts for realignment, for use with electron sensitive
photo resist target members, etc. employed during microcircuit fabrication or
the like using such electron beam tubes;
Figure 27 is a partial sectional view of another form of micro lens
array and deflector assembly according to the invention wherein the micro lens
plates and micro deflector ara assembled with small sapphire balls seated within
holes, sockets and/or spacer elements and clamped together for subsequent easy
breakdown and reassembly;
Figure 28 is a plan view of a micro lens plate having specially
designed shapes for the lens apertures fabricated according to the invention for
electron beam aberration correction purposes;
Figure 29 is a series of cross-sectional views of still another
embodiment of micro lens array sub-assembly according to the invention where
five etched semiconductor plates comprise the array;
-16-
1157~1~
Figure 30 is a plan view of still another form o etched silicon
semiconductor micro lens array plate according to the invention wherein
extremely thin lens plates of the order of 2 microns (2~) in thickness are
provided; and
Figure 31 is a cross-sectional view taken through plane 31-31 of
Figure 30 of the extremely thin micro lens array plate shown in Figure 30.
DETAILED DESCRIPTION OF PREFER~ED EMBODIMENTS
Figure l is a sectional view taken through plane l-l of Figure 2 of a
preferred form of Dlicro lens array and micro deflector assembly according to the
invention. As sho~n in Figures 1 and 2, the assembly is comprised by a micro
lens array sub-assembly shown generally at 11, a micro deflector sub-assembly 12
a target assembly shown generally at 13, and a plurality of elongated glass
support rods two o~ which are shown at 14 and all of which extend at substanti-
ally right angles to the plane of the micro lens array plates comprising the
micro lens array sub-assembly and the plane of the micro deflection bars
comprising the micro deflector assembly. In addition, the assembly further
includes a termination plate shown at 15 which comprises a part of the micro
lens array sub-assembly as will be explained more fully hereafter.
The construction bf the micro lens array sub-assembly is best seen in
Figure 3 and Figure 4 of the drawings wherein it is shown in ~igure 3 that the
micro lens array is comprised essentially of a plurality of three ~3) (but could
be four (4), five (5) or more or less as needed for a particular application~ of
spaced-apart, stacked, parallel, thin, planar, apertured lens plates 16, 17 and
18 each of which is fabricated from siliçon semiconductor ma~erial which
preferably is single crystal silicon. As will be described more fully hereafter,
each of the thin apertured silicon lens plates has an array of micro lens
-17-
1157~1~
aperture openings formed therein by photolithographic semiconductor microcircuit
fabrication techniques with the remaining surfaces of the pla~es being highly
conductive The apertured silicon lens plates 16, 17 and 18 are secured by
thermal bonding or otherwise to glass support rods 19 arrayed around their
outer pcriphery for holding the lens plates in stacked, parallel, spaced~apart
relationship. While securing the lens plates 16, 17 and 18 in assembl~d
relationship on the glass support rods 1~, the lens aperture openings in all of
the silicon lens plates are axially aligned along longitudinal axes passing
through the center of each aperture opening and which are at right angles to the
plane of the plates. This is achieved by means of alignment notches ~ormed in
the starting silicon wafers from which the aper-tured lens plates are fabricated
in a manner to be described more ully hereafter or alternatively may be
achieved by means of electron optical or light optical alignment techniques.
Axial alignment of the lens aperture openings in each of the respective thin
silicon plates 16, 17 and 18 commences with the placement of photo resist
patterns employed in forming the aperture openings on the starting thin silicon
wafers and are used right on through to assembly of the several lens plates
together onto the supporting glass rods 19. In mounting the thin silicon
plates to the glass support rods, the peripheral edge portions o the thin
silicon plates are thermally bonded onto the glass rods by heating the glass
rods to substantially their melting point. At the temperature where the glass
rods commence to soften, the rod is physically pressed into the periphery of
the stacked and aligned plates supported in a suitable holding fixture with the
array of aperture openings therein axially aligned as described above and
thereafter the glass rod is allowed to cool. Different electrical excitation
potentials are supplied to the thin silicon plates in ~he manner best shown in
-18-
-115~Sll
Fi~ures 19 and 19A of the drawings. In Flgure l~ it will be seen that a small
conductivc wire such as nichrome has one exposed end shown at 20 trappcd
aetween the edge of the thin silicon plate 17 ancl the supporting glass rod 19
during thermal bonding. The remaining end of wire 20 is bent over as shown by
dotted lines at 20A to connect to the exposed encl oE a conventional insulated
lead-in conductor 20B for the excitation potential to be applied to plate~ 17.
In Figure 19A a small nichrome washer 20C that contacts the outer conductive
surface of plate 17 is seated between a pair of nesting, coaxially aligned,
glass rod insulator segments having two different diameter, cylindrically-
shaped end portions. By clamping a suitable number of such insulator segmentstogether and tailoring their longitudinal extent, proper spacing between the
lens plates can be obtained. By thus assembling the micro lens array, the
respective thin apertured silicon lens plates 16, 17 and 18 (which may have a
thickness of the order of 1/2 millimeter in thickness and are spaced-apart
approximately one and one~half millimeters) are capable of sustaining a voltage
difference between plates of the order of S to 10 kilovolts without breakdown
and conduction between adjacent plates. In place of nichrome, a metal which
alloys with silicon could be used to form the contacts 20 or 20C, thereby
assuring secure electrical contact of the lead-in conductor to the thin silicon
plates.
With tlle stacked, parallel apertured thin silicon plates comprising
the lens array secured to the glass support rods 19 in the above described
fashion, the glass support rods in turn are fastened by suitable mounting tabs
shown at 21 to an annularly-shaped outer support ring 22 which also supports the
termination plate 15. The mounting tabs 21 are generally trapezoidal in con-
figuration as shown and have an essentially half-heart shaped depression formed
-19-
~1~7511
in the end thcreof for engaging the glass support rods to assure permanent and
soli~ ~ecu~emellt to the glass support rocls after cooling. Placement of the
~ounting tabs 21 in the glass support rods may of course take place concurrently
with the securement of the thin apertured silicon plates 16-18 to avoid the
necessity for therm~l recycling of the glass support rods in t~o dif-ferent
operations, ho-~ever, in advance of securing the mounting tabs 21 to the glass
rods, the mounting tabs are first brazed, or otherwise secured to the annularly-
shaped, support rings 22 which may be formed from molybdenum, tungsten, or
other suitable metal for providing electron optically clean surfaces after
bake-out within an evacuated housing enclosure.
The construction and purpose of the termination plate 15 is described
more fully in a paper entitled "Computer-Aided Design and Experimental
Investigation of an Electron-Optical Collimating Lens" by C.T. ~ang, K;J. }-larte,
N. Kurland, R.K. Likuski and E.C. Doherty appearing in the Journal of the
Vacuum Society Technology, Vol. l0, no. 6, November/December 1973, pages 110-
113. Briefly, it can be stated that the termination plate 15, sometimes referred
to as a "tuning plate" serves to terminate electric fields employed in the
coarse deflection section of ~he fly's eye type electron beam so that such fields
do not enter and adversely influence the behavior of the micro lens array and
micro deflector assembly. Upon assembly of the micro lens array in a fly's eye
electron beam tube, electron beams transiting the sub-assembly enter through the
termination plate 15 and exit through the lens aperture openings of the last or
lowermost silicon plate 18. Thus, plate l~ is physically disposed adjacent the
micro deflector sub-assembly and may be subject to the influence of the relativ-
ely high frequency (of the order of megahertz or perhaps even gigahertæ
frequency) deflection potentials applied to the respective deflector plates of
-20-
115~51~
the micro dcflector assembly. To assure that plate 18 remains rigid, a stiffen-
ing ring 23 of molybdenum, tungsten or other suitable compatible metal is
secured to the outer periphery of the lowermost thin silicon plate 18 by means
of thc additional mounting tab 21A. For the best thermal match, stiffening ring
23 should be ~abric~ted from polycrystalline silicon of sufficient thickness to
provide the rc~uired stiffening.
As best shown in Figure 17 of the drawingsJ lens aperture openings
(hereinafter referred to as apertures) can be provided which are of exceptional
s~mmetry (e.g., roundness) due primarily to the etching qualities of single
crystal high purity silicon. By using boron diffusion patterns to provide sharp
etching outlines in the silicon substrate, it is possible to provide these
exceptional symmetry apertures in the lens plates for each set of axially
aligned micro lens apertures, and to do so for the entire array of apertures to
be formed in a single thin silicon wafer (e.g., 128 by 128 array of apertures)
in a single processing operation. The sets of axially aligned apertures in the
respective thin silicon lens plates 16, 17 and 18 are axially aligned with
a respective set of micro deflector elements for any given channel. ~ channel
is defined as an electron beam path provided by an axially aligned set of micro
lens apertures and the coacting axially aligned micro deflector elements as
described more fully hereinafter. A preferred axial profile for each axially
aligned set of micro lens apertures defining any given channel is shown in
Figure 17. Referring tG Figure 17 it will be seen that each channel is comprised
of four lens plates 16J 17~ 18 and 18A. The fourth plate 18A may or may not be
used depending upon the storage density desired. A very small aperture 31 of
about 2 microns ~2~) diameter is formed on the top surface of the top thin
silicon aperture plate 16 on the electron beam entrance side of the assembly.
-21-
~157511
This sm~ll aperture 31 is ormed through a highly condwctive surface portion 33
of the lens plate 16 that is produced as a result of the process in which the
aperture 31 was formcd. As stated above, because of the process and the manner
in which it was formed ~to be described hereafter) the aperture 31 is of
exceptional syl~netry about a central a~is e~tending through the center of the
aperture 31 and perpendicular to the planar surfaces of the thin silicon plate
16. A second or outlet aperture 32 likewise of exceptional symmetry and centered
about the same central axis as aperture 31~ is formed on the bottom surface of
the lens plate 16 which also has a highly conduc~ive surface area 34. Inter-
mediate portions of the silicon wafer extending between the apertures 31 and 32are etched back away a slight distance as shown at 35 in order to assure that
only the highly conductive aperture sides 31 and 32 which are precisely formed
and of exceptional evenness and symn~etry are effective to produce an electric
field that influences an electron beam passing through the lens element.
The second apertured thin silicon lens plate 17 has apertures 36 and
37 formed in the respective top and bottom surfaces thereof which are of
substantially equal diameter and likewise are formed within highly conductive
surface portions 33 and 34 of the thin silicon lens plate 17. In this lens
plate, the outwardly sloping side surfaces 38 and 39 of each aperture project
outward in~o the body of the semiconductor plate 17 from the respective apertures
36 and 37 and intersect at some mid-point spaced outwardly from the peripheral
- circumference of the equal diameter apertures 36 and 37 so as again not to
influence the electron beam and assure that only the sides of the apertures 36
and 37 which are designed for that purpose, produce electric fields that affect
the electron beam.
The third plate 18 of the stacked parallel lens plate has a larger
" 11575~
diamcter aperture ~ll formed in its upper or clectron beam entrance side in
contrast to a very small diameter exit aperture 42 formed on its lowcr conduct-
ive surface portion 34. ~lere again, the sloping s.ide surfaces 43 of the
intervening silicon semiconductor body port.ion of plate 18 are etched a
sufficient distance bac~ away from the peripheral edges of the apertures 41 and
42 to assure that the intervening semiconductor oE the silicon plate does not
influence an electron beam passing therethrough. The last plate 18A in the array
~if used) is idcntical in construction to the top plate 16. In assembling
the stacked, parallel silicon lens plates 16, 17, 18 and 18A in the manner
described previously, the respective longitudinal axis passing through the
aperture 31 in lens plate lG also constitutes the common axis for all of the
axially aligned apertures further comprised by 32 in plate 16, 36 and 37 in
plate 17, 41 and 42 in plate 18 and 31 and 32 in plate 18A (if used). Further,
it should be kept in mind that an entire array of such axially aligned lens
apertures arc provided by the assembled micro lens plates wherein if there is a
128 by 128 matrix of lens elements provided in the array, Figure 17 would have
to be projected outwardly from each side to illustrate the additional 127
axially aligned lens elements arrayed along a single plane. Again, ideally,
the center axis pass;ng through each axially aligned set of array elements is
parallel to all of the other center axes and all in turn are perpendicular to
the plane of the thin silicon plates 16, 17, 18 and 18A, respectively.
The lens plates shown in Figure 17 provide uniformity and exceptional
symmetry in the placement of the small diameter lens apertures such as 31 and
42 in the small diameter regions of the axial profile shown in Figure.17. It is
also necessary that the plates 16, 17, 18 and 18A exhibit great rigidity because
while in use they are in high field gradients and are thus subjected to strong
1~7Sll
deflectio}l forces. The deflection forces can strongly influence the lens
performance if the apertures do not possess a high degree of axial symmetry.
This is due to the fact that the lens plates tend to deflect under the pull of
the electric field applied between the plates so that the spacing of the lenslet
elements near thc center of the plate will be less than the spacing of the
lcnslet elements near the edges. To a first approximation, the spacing change
does not cause any great disturbance since the stronger field created by the
shorter distance in the center is in part offset by the shorter distance over
which the field is applied. However, the outer lenslet elements experience a
tilt as well as an infinitesimal radial displacement and this can cause some
lens error of the type known as comma. For this reason, it is desirable that
the plates bc dcsigned to deflect as little as possible upon being placed in
operation. The axial profile shown in Figure 17 permits a high stiffness or
rigidity to weight ratio for optimum array densities versus center to center
spacing of the lenslet elements thus providing a structure with a small mass
which is required for use of the glass rodding assembly technique but which
also possesses the required stiffness to prevent excessive deflection under
electric field stress. By way of illustration, a silicon lens plate of
approximately 3 inches in diameter and 1/2 millimeter thickness with a spacing
between plates of about 1 millimeter, the total unbalanced forces on the plate
are of the order of 1/2 lb. and the centered displacement is of the order of 50
micrometers (50~) leading to a maximum tilt of less than 1/2 milliradiand which
gives an acceptable lens performance.
The required aperture profile can be provided by a variety of known
photolithographic and etching techniques used in the fabrication of semiconductor
microcircuits. A preferred technique for fabricating apertured micro lens array
-2~-
~ l S~
thin silicon platcs is illustrated in Figures 18A through 18J. For starting
material 3 an N-type single crystal silicon wafer 17 of approximately 1/2
millimeter thickness and 100 orientation shown at 17 is provided. Suitable
alignment notches shown at 51 are cut into the periphery of the wafer to
facilitate positioning of the photomasks employed'ill forming masking areas on
the surfacc of the silicon wafer and also in subsequently aligning the wafer
with other aperturecl lens plates used in thc micro lens array. A wet silicon
oxide layer then is grown on both sides of the silicon wafer as shown at 52 and
53 in Figure 18B of the drawings. After growing the oxide layers on each side
of the wafer, chromium alignment dots are formed on one surface at the outer
edges by photolithography masking techniques and exposure oE one surface of
the wafer, such as 52, to a chromium vapor atmosphere to thereby produce the
chromium alignment dots 5~, as shown in Figure 18C. Using the chromium
alignment dots and the notches in the periphery of the wafer, and again using
photolithography techniques, an array of silicon oxide dots are produced where
apertures are to be formed in the wafer as shown at 55 in Figure 18D. Each of
the silicon oxide dots in the array should be of the same size and shape as the
apertures to be formed in the wafer. After the oxide layer has been processed
to form the oxide dots 55, the chromium aligmnent dots are removed. During
this process the notches and back side of the wafer are protected with wax or
other suitable protective coating.
The next step in the processing is to produce an array o~ oxide dots
on the remaining untreated side of the wafer which, as shown in Figure 17, may
be of the same size or different size from the oxide dots formed on the
previously treated side. If the wafer in question is being processed to produce
an end plate, the oxide dots on the two sides of the wafer will be of different
11~751~
size but l~ill have the same centers ~e.g., axially-aligned) as dcscribed
previously. This is achieved using infrared techniques to assure alignment
of the silicon oxide dots on both sic1es o~ the ~afer during the photolitho-
graphic processing to produce the second set of oxide dots. The resultant
array of oxide dots on the remaining surface are shown at 56 in Figure l8E.
At this point in the processing, the wafer is spin coated with a boron
containing emulsion with the emulsion being spin coated on both sides of the
wafer. The boron containing emulsion coated wafer then is fired in a furnace
at about 1100C. in a nitrogen atmo5phere. During this processing, the boron
dopant contained in the emulsion will diffuse into the surface of the silicon
wafer to a depth of about 2 microns at which point the firing is discontinued
as shown in Figure 18F to result in a boron coated surface layer 33 where
no apertures are to appear as best seen in Figure 1811. The excess boron coat-
ing is removed in a hydrofluoric bath followed by a second bath in fresh
hydrofluoric acid to remove the oxide buttons. This processing step leaves a
deep and heavy boron layer formed in the surface areas of the wafer where it is
desired that no apertures be formed and results in sharply defining the undoped
silicon aperture opening areas as shown at 55A and 56A in Figure 18G which are
of quite even symmetry since the boron diffusion step is extremely uniform
throughout. In a final processing step~ the boron doped wafer is etched in a
hot pyrocatec11ol and ethylene diamine bath as described in the article entitled
"Ink Jet Printing Nozzle Arrays Etched in Silicon" by E. Bassous, et al. reported
in Applied Physics Letters, Vol. 31, no. 2, July 15, 1977, pages 135-137. As
taught in this article, the orientation rate dependence causes the etching
action to stop when the sloping planes from under the two apertures being formed
on opposite sidcs of the silicon wafer meet. Consequently, the underlying
-26-
l lS~51~
silicon support for the apertures defined by the boron doped layer that now
conatitutes the remaining surface arcas of the silicon wafer 17 is somowhat
undercut belo~-~ the boron doped layer 33 as shown in ~igures 17J 18 and 18I
to result in apcrtures of exceptional symmetry and evenness as depicted in
Figures 18I and 18J of the drawings. In this respect, it should be noted that
the profile of the silicon support underlying the thin boron doped layer 33 is
not critical. The key factor is the thin surface boron doped layer 33 that
defines the aperture (opening or hole) which must not be destroyed by the
etchant used in etching away the silicon support intermediate the axially
aligned aperture openings on each of the opposite sides of the silicon wafer.
While there are a variety of ways known to the art for accomplishing differ-
ential etching action as described aboveJ the preferred method is as dislcosed.
The above description was with relation to the production o the
center lens plate wherein the aperture openings on each side of the plate have
substantially the same diameter. The technique described is not limited to
fabrication of lens aperture plates of this type for it may also be used in
fabricating the end plates wherein the aperture on one side of the plate is
smaller than the aperture on the opposite side of the plate, as well as other
configurations as depicted in Figure 28.
Figure 5 is an end plan view of a micro deElectorsub-assembly constructed
in accordance with the invention and ~igure 6 is a partial cross-sectional
view of the deflector sub-assembly taken through plane 6-6 of ~igure 5. As
best seen in ~igure 5, the micro deflector sub-assembly comprises two orthogon-
ally arrayed sets of parallelJ spaced-apart, deflector bars 61 and 62 which are
arrayed at right angles to each other so as to define a plurality of orthogon-
ally arrayed sets of micro deflector elements. As will be described more fully
__
1 1 3 7 ~ 1 ~
herea~ter, alternate ones of each set of orthogonally arrayed deflector baTs 61
and 62 are electrically interconnected Eor common connection to a respective
source of fine x-y deflection potential for deflccting an electron beam passing
througll any selected one of the micro deflector elemen-ts in a d:irection at
substantially right angles to thc path of the electron beam in ei*her the x or
y direction For example, considering the x and y axis to be as indicated in
Figure 5, then ~he ~ axis deflection potential applied between alternate ones of
the deflector bars 62 will cause an electron beam passing through any selected
one of the micro deflector elements to be deflected right or left as viewed in
Figure 5 along the x axis depending upon the polarity and magnitude of the fine
x deflection potential. Similarly, the fine y deflection potentials applied
to alternate ones o~ the deflector bars 61 cause deflection of an electron
beam passing through any selected one of the micro deflector elements along the
y axis in a manner dependent upon the polarity and magnitude of the fine y
deflection potentials applied to alternate ones of the deflector bars 61. Thus,
it will be appreciated that the intersection of the orthogonally arrayed sets
of deflector bars 61 and 62 at their points of intersection define an entire
array of fine deflector elements since the deflector bars are spaced apart one
from the other and at each intersection point of the orthogonally arrayed bars
an essentially square-shaped, fine open space exists which defines the micro
deflector element within the points of intersection. This micro deflector
element or open space is arranged so that it is axially aligned with a
corresponding set of micro lens aperture elements formed in the micro lens
array sub-assembly as previously described. For this purpose, extreme care
must be taken when assembling the micro deflector sub-assembly with the micro
lens sub-assembly as described heréafter in order to assure the proper axial
-28-
1157511
alignment of each respective micro-deflector element with its corresponding
micro lens axially aligned aperture openings.
~ ch of the micro cleflector bars 61 and 62 preferably is ~abricated
from polycrystalline silicon as will be described hereafter in connection with
~igures 20, 20A through 2Q~ and the surfaces thereo may be metalized wikh a
platinum coating or other suitable highly conductive metallic meterial. As
best seen in Figure 20, the fine deflection bars 619 62 preferably are sawed
from a rectangular-shaped block 63 of polycrystalline silicon having grooves
sho~yn at 64 and 65 sawed or otherwise formed in each of the ends thereof. As
best shown in the end view of Figure 20A, the groove 64 is spaced from the end
of the block of silicon 63 a greater distance "a" than is the groove oS which
is shown as being spaced a snlaller distance 'Ibl' rom the end o the block of
polycrystalline silicon. The purpose or making the dimensions "a" and "b"
different from one another will become apparent hereafter but it should be
noted that the fine cleflector bars 62 are fabricated in an idential manner
and with essentially the same "a" and "b" dimension. Thus, after fo~ming the
grooves 64 and 65 in the block of polycrystalline silicon 63J the individual
blades 61, 62 are sawed from block 63 in the manner indicated in Pigure 20.
In constrast to aluminum oxide or other comparable ceramic, silicon is not
nearly so hard so that tool wear in sawing the inclividual silicon deflector
bars 61, 62 from the block of silicon is not a significant problem. At this
point in the fabrication, the deflector bars 61, 62 are plated with about a
2000 Angstrom units thick coating of heavy metal such as platinum or gold
preferably by an ion plating technique such as described in the article en-
tltled "Electron Beam Techniques for Ion Plating" b~ D. Chambers and D.C.
Gharmichael reported in Research/Development, volume 22, May 1971, or alterna-
~ 2~ _
7 ~
tively by vapor drposition as described in the article entitled "PhysicalVapor Deposition" by Airco Temescal Staff ~1976), R.J. Hill, Director ~page
60~. Other known metalization techniques and procedures also may be employed
to provide the metal coating havlng good adhcrence and thickness of the order
of about 2000 Angstro~ units. Prior to metalizing the surfaces of tlle sawed
deflector bars, it may be necessary to lap finish each of the bars to remove
burrs and other surface irregularities prior to the metalization step.
Figures 20B and 20C are a plan view and side end view) respectively,
of a suitable holding fixture for assembling the ~icro deflector plates to-
gether in a spaced-apart, parallel assemblage. In Figure 20B, a square or
rectangular block of silicon shown at 66 again is employed and has a plural-
ity of slots such as shown at 67 cut therein to a suitable depth that will
insurc mechanical rigidity of holding action UpOll the respective metalized
deflector bars fabricated as shown at 20 and 20A inserted theTein in the manner
indicated in Figure 20Co The slotted silicon block 66 after fabrication forms
a fixture that can be reused in assembling further micro deflector sub-assemb-
lies as described hereinafter. Because it likewise is formed of silicon, it
is thermally compatible with the blades which are being held by the fixture
and hence will reduce or minimize stresses which might otherwise be encountered
in the assemblage steps to be followed as described hereafter~
Figure 20D shows a preferred procedure for assembllng one set of the
deflector blades such as 61 together in a parallel spaced apart relationship by
means of a glass supporting rod shown at 6~ The metalized silicon bar or
blades 61 (or 62) are held upside do~n in the slots 67 cut in the silicon hold-
ing fixture 66 with the grooves 64 and 65 facing upwardly and aligned along
an axis looking into the plane of the paper~ In so placing the blades, they
- 30 -
~1~751~
are alternated en~ for end so that alternate bars have the groove 64 axially
aligned with the grooves 65 in the remaining set of alternate bars. A glass
support rod 68 then is placed in the axially aligned, alternate grooves 6~ and
65 formed at each end of the parallel array of deflector bars as shown in
Figure 20D. A thill conductor wire or ribbon of platinum shown at 69 is then
placed adjacent the elongated ends of alternate bars having the dimension "a'
bet~een the grooves 64 and the ends of the bars and a pressure pad 71 is
applied to force tlle conductor wire 6~ into positive engagement with the elon-
gated ends of alternate ones of the blades 61. At the opposite side of the
fixtureg a similar arrangement is employed to bond a corresponding conductor
ire 69 to the end of the remaining alternate sets of deflector bars 61. The
ixture 66 is supported on a table of adecluate strength and a second pressure
pad indicated at 72 is applied domlwardly across all of the deflector bars 61
to be assembled and concurxently hea~ is applied through a suitable heating
tool to cause the glass support rods 68 to become heated to a temperature close
to its melting point so that it softens and thermally bonds to the individual
deflector bars at their points of contact with the glass support rod. ~oncur-
rently, heating current is supplied through the thin platinum conductor wire
69 to cause it to thermally bond to the ends of the metaliæed silicon bars and
form good positive electric contact therewith. Upon cooling of the glass sup-
port rod 68, ail of the de1ector bars 61 will be thermally honded to the glass
support rods. Thereafter, the holding fixture 66 can be removed and used again
in the assembiage of a second set of deflector bars. Because the holding fix-
- ture 66 is of the same material as the deflector bars~ mechanical discrepancies
and stresses duc to thermal differences in the materials that might otherwise
be i~uilt in during the heating and cooling phases of the asseinblage operation,
115'~511
are avoidedO A similar assemblage technique then is employed in mounting the
second set of de1ector bars 62 to their corresponding glass support rods thus
resulting in tlle two sets of spaced-apart, parallel deflector bars 61 and 62
requirecl to form the micro deflector sub-assembly first described with respect
to Figures l, S and 6 of the dra~ings.
Figure 20D also illustrates schematically an alternative scheme for
applying the required lead-in conductor wires to alternate deflector blades or
~ars and employing an alternative form of conductor wire 69A. The alternative
conductor wire 69A can be circular in cross section, flat or any desired cross-
s.ectional configuration since it is designed to fit into the ~roove 64 belo~the glass support rod 68 and extend along the top edges so as to contact and
fuse to alternate blades or bars 62~ For this purpose, it would be necessary
to machine tlle two grooves 64 and 6S to different depths rather than different
end displacements "a" and "b" and arrange them alternatively. The alternate
conductor wire 69A then should have sufficient thickness to be engaged by and
compressed somel~hat by the glass support rod 68 UpOII being pressured into en-
gagement with the sides of the groove 6~ during thermal bonding o the glass
support rod to the blades or bars 61. With the alternate lead-in contact
arrangement using the alternate conductor wire 69A it would not be necessary to
2Q provide the additional pressure pad 71 except for end alignmellt purposesO
l~hile two alternate methods for applying excitation potentials to the alternate
micro deflector bars have heen disclosed, it is believed obvious to one skilled
in the art that a cross bar connector could be used across the tops of the sets
of bars wherein alternate deflection bars would be brazed or otherwise connected
to the cross bar connector and the intervening bars where no electrical connec-
tion is to be provided an insulating space would be provided. Other suitable
- 32 -
arrangements likewise could be employed and would be obvious to those skilled
in the art in the light of the above teachings;
In addition to the metalized silicon deflection bars fabricated in
two orthogonally arrayed sets as described above and shown in Figure 5 of the
drawings, each set of spaced-apart parallel deflector bars include elongated,
end bars 61A and 61B which are parallel to the deflector bars 61 and elongated,
end deflector bars 62~ and 62B whîch aTe parallel to the deflector bars 62.
The elongatedJ end deflector bars 61A, 61B, 62A and 62B all preferably comprise
a suitable polished nonmagnetic metal bar such as molybdenum, tungsten or
other similar metal that can be made electron optically clean and which provides
s.ufficient rigidity to serve as a mounting means for mounting the sets of
spaced-apart parallel metalized silicon deflector bars in place within the
evacuated housing of an electron beam tubeO It is also desi~able that at least
the ends of the elongated, end deflector bars 61A-62B be malleable to the ex-
tent that they can be bent to conform to a configuration whereby they can be
clamped to a mounting ring or other supporting member located at a particular
point within an electron beam tube housing~ The micro deflector sub-assembly
shown in Figure 5, however, utilizes elongated, end deflector bars 6lA~6lBJ62A~
and 62B wherein the ends of the bars project well beyond the glass support rods
ZO 68 to which they are likewise thermally bonded in the same heat treating pro-
cess by which the metalized silicon deflector bars were secured to the glass
support rods. The ends of the elongated, end deflector bars serve as mounting
tabs for securement to an annularly-shaped metallic support ring 73 whereby
each of the sets of the orthogonally arrayed, parallel, spaced-apart metalized
silicon deflector ~ars 61 and 62 can be mounted in spaced-apart and juxtaposed
relation~ In order to minimize the spacing between the two sets of deflector
- 33 -
1 :l575 1 1
bars 61 and 62, the ends of the elongated end deflector bars GlA and 61B are
~ounted to the upper surface of the support ring 73 as viewed by the reader,
while the ends of the elongated, end deflector bars 62A and 62B are secured to
the under-surface of the support ring as shown in Figure 5. ~igure 6 of the
dra~ings is a cross-sectional vie~ of the micro deflector sub-assembly wherein
it can be seen that the two sets of orthogonally arrayed, spaced-apart, parallel
deflector bars 61 and 62 are spaced apart a short distance relatlve to the
width of the bars, ~hich distance may be of the order of only several milli-
inches
Figure 7 of the drawings is a cross-sectional vie~ of the target
electrode sub-assembly employed with the overall mlcro lens array and micro
de1ector assembly shown in Figure 1. The target electrode sub-assembly 13
comprises a metal-oxide se~i-conductor mel~ory capacitor structure which may be
of the type described in United States Patent Number 4,079,358 issued March 14,
1978 for a "Buried Junction MOS Capacitor Target for Electron Beam Addressable
Memory and Method of Using Same," Floyd O. Arnt~, inventor, The MOS memory
capacitor target member indicated generally at 13 is mounted for support on a
airly massi~e donut-shaped cerc.mic mounting member 81 having the MOS nlemory
capacitor target member 13 supported over a central opening 13A thereinO Bias
potential as well as signals derived during read-out of the MCS memory capa-
citor target member are supplied through an insulating terminal ~not shown) for
application to the upper (closest to the micro deflcctor sub-assembly) conduc-
tive surface of the MOS capacitive target member as described in the above-
referenced United States Patent Number 4,079,358. The backing support member
81 and a cup-shaped shield 83 are secured to an annularly-shaped outer support
ring 84 or mounting to the axially extending common glass support rods 14.
- 34 -
115~511
As best seen in Figure 1 considered in conjunction with Figure 8 of
the drawillgs, the metallic mounting ring 22 for the micro lens array sub-
assembly is bra~ed or otllerwise secured to the inner peripheral edge of a cup-
shaped outer support ring 85 that in ~urn is secured by trapezoidally-shaped
mounting tabs 86 to the axially extending, peripherally arrayed glass support
rods 14. In a similar manner, the outer support ring 73 for the micro deflector
sub-assembly has its outer peripheral edge brazed or otherwise secured to the
inner peripheral edge of a disc-shaped, metallic outer support ring 87 that is
$ecured to the axially extending, peripherally arrayed glass support rods 14 by
mounting tabs 88. Lastl~, the support ring 84 for the target electrode sub-
assembly 13 is brazed or otherwise secured at its outer periphery to the inner
periphery of a second annular disc-shaped metallic mounting ring ~9 that in
turn is secured to the axially extending glass support rods 14 by mounting tabs
~0. During assembly o each of the micro lens array sub-assemblies to axially
extending glass support rods 14 by brazing or other wise securing the support
ring 22 to the outer mounting or support ring 85, proper axial alignment of the
array apertures relative to the lens element of the micro deflector sub-assembly12 and to the target electrode member 13, is maintained by insertion of align-
ment rods in alignment notiches or aperture openings formed in the respective
mounting rings 22 as shown at 91 in ~igure 4, in mounting ring 73 as shown at
92 in Figure 5, and in mounting ring 84 (the alignment notch o which is not
shown). If desired, electron optical and/or light optical alignment procedures
could be used in place of or to augment the mechanical alignment procedures
noted aboveO
After assembly together in the above-described manner as shown in
~igures 1 and 2 of the drat~ings, the resulting micro lens array and micro de-
flector assembly together with termination plate for the coarse deflection sec-
- 35 -
115~5;~1
tion and target electrode member will be seen to have been fabricated from
silicon either in single cr~stal or polycrystalline form and glass to the
greatest extent possible so tilat all parts of the assembly have comparable
thermal proyerties alld possess essentially the same thermal coefficient of
expansion to the greatest possible extent. A number of the parts are processed
in accordance Wit}l semiconductor microcircuit fabrication techniques which
provide exceptional quality roundness, symmetry and evenness of the aperture
openings in the micro lens array together ~ith exceptional symmetry in the
spa~ing betl~een openings. The entire assembly is held ~ogether by glass rod-
ding or other similar material insofar as possible. The advantages obtained byfabrication of t11e assembly in this manner are that it reduces the cost and
comple~ity of measures otherwise required to guard against rapid temperature
changes between different parts of the electron optical assembly since the
glass and silicon parts have substantially the same temperature coefficient of
expansion. Silicon employed in the fabrication of most of the parts has great-
er stiffness and much better dimensional stability and can be used without
closeby support rings or belts thereby making possible any desired lens plate
thickness and any lens plate to lens plate spacing. It is much easier to cut
and metalize silicon than fired ceramic or other material heretofore used
thereby making the problem of find deflector plate fabrication much less costly
and better controlled. ~owever, it should be understood that the use of cera-
mic deflector plates is not precluded~ The fabrication techniques herein des-
cribed result in an electron optically clean structure and, in addition, allows
flexibility in forming the deflector bars so as to facilitate later assemblage
and connection of deflection potentials to the bars.
Figures 9 and 10 of the drawings illustrate the new and improved
micro lens array and micro deflector assembly used in conjunction with a diff-
erent type of target member from that shown in Figure lo The arrangement shown
- 36 -
1 1 5 ~5 1 ~
in Figure 1 oF the drawings is for use ~ith electron beam accessed mcMories
employed in computer systemsO The arrangements shown in ~igures 9 and 10 of
the drawings are intended for use in semiconductor microcircuit fabrication or
other comparable electron beam de~ined art work. For this reason, the arrange-
ment shown in ~igure 9 includes a removable, electron sensitive target member
91 which is disposed i~led;ately adjacent the micro deflector assembly on the
electron beam exit side thereof for impingement of electrons thereon after
deflection o the electron beam by the micro deflector sub-assembly 12. The
electron sensitive target member 91 may comprise a photo-sensitive plate where
the apparatus is being used for imaging or for alignment purposes, or the like,
or alternatively, it may comprise an electron sensitive photo resist covered
wafer having its electron sensitive surface placcd opposite the 0xit side of the
micro deflector assembly 120 The electron sensitive member 91 is clamped in
place on a plate holder 92 by a set of clamps indicated at 93 which are arranged
around the periphery of the plate or member 91. The electron sensitive plate or
member 19 together ~Yith the plate holder 92 are held in place over the end of an
evacuated tube, the outer housing or envelope of which is shown partially at 94
by reason of the vacuum produced within the interior of housing 94 by a vacuum
apparatus (not shown~ connected to the housing for the purpose of drawing down
the atmosphere of the housing to low vacuum levels. In order to facilitate
changing of the electron sensitive plates 91, a gate valve structure is pro-
vided which is designed to close over a central opening in the end wall 95 of
the tube housing 94D During operation of the tube, the central opening in end
wall 95 will be closed by the plate holder 92 and the electron sensitive member
91 held in place over the op0ning through the force of the vacuum and exterior
atmospheric pressureO In order to change the electron sensitive plate member 91
- 37 -
1~575~
after processing o~ the same, a linearly tr~mslatable gate valve memler 96 is
provided which can be slid into place over the centre opelling in end wall 95
and sealed against an 0-ring seal 97 through actuation of a set of locking cam
members shown at ~80 With the ga-te valve member 96 in place over the central
opening in the end wall 95~ the electron sensitive target member 91 and plate
holder 92 can be removed without complete loss of vacuum within the tube hous-
ing 94. Upon completion of the change of the electron sensitive target member
91, the gate valve 9G can be linearly withdrawn to the position indicated in
Figure 9 by appropriate actuation of the cam members 98 after placement of the
new electron sensitive target member 91 and plate holder 92 ~ack in position so
that they are exposed to the interior of the housing as gate valve member 96 is
withdrawn and the housing again pumped down to a suitable level of evacuation.
The micxo lens array and micro deflectox target assembly 11, 12 as
secured by means of a support ring 99 to a glass mounting ring or belt 101
thermally bonded to the exterior periphery of the coarse deflector cone 100 at a
point adjacent the end ~5 of tube 9~O Support ring 9~ forms a "housekeepers
seal" by means of a thin depending skirt portion that is embedded in the glass
mounting ring 101 during thermal bondingO An 0-ring seal disposed between the
external periphery of support ring 99 and the internal circumference of outer
housing envelope 94 completes the strwctures. ~y this construction, the amount
of metal contained within the interior of the housing 9L~ is reduced to a mini-
mum for purposes discussed above and the overall weight of the assembly and ~he
effect of different temperature coefficients of expansion in the material used
in constructing the assembly, are reduced to a minimum.
In the embodiment of the invention shown in Figure 9, the coarse de-
flector section 102 of the coarse deflector cone 100 is disposed intermediate
115751~
an electron gun asscmbly 103 for producing a fine, pencil like beam of elec-
trons and the micro lens array and micro deflector assembly ~11J 12). The
coarse de~lector section 102 preferably is designed pursuant -to the teachings
of United States patent application Serial Number 812,981, filed July 5, 1977,
Kennctll J. Ilarto, inventor. The electron beam projected fro~ the electron gunassem~ly 103 throu~ll the coarse de1ector sec~ion 102, i5 selectively deflectedby the coarse deflector to pass through a selected one of the 128 by 12~ array
of aligned openings in the termination plate 15~ The electron beam then passes
thXough the corresponding axially aligned lenslet apertures in micro lens array
sub-assembly 11 and the axially aligned micro deflection element in Ihe micro
deflector sub-assenlbly 12 to thereafter selectively impinge upon the electron
sens,itive target member 91 at a point determined by the fine x-y deflection
voltages applied to the micro deflector sub-assembly~ By this means, extreme-
ly fine control o~er the positioning of the point of impingement of the elec-
tron beam on the electron sensiti~e target member 91 is achieved.
The embodiment of the invention sholyn in Figure 10 difers from that
of Figure 9 in that it employs a different form of electron gun asse~bly 103.
The Figure 10 species preferably uses a field emission type oP eleckron gun for
producing a flood of electrons that are directed through a graded field struc-
ture sho~n at 104 which completely circumscribes the interior surface of thecoarse deflector cone 90, and which is used in place of the coarse deflectors
102 employed in the Figure 9 arrangement~ The graded field structure 104 is
designed to produce a uniform flood o electrons that covers the entire surface
of the termination plate 15, and hence uniformly simultaneously passes electron
beams of reduced beam current through all the micro lenslets in the sub-assembly
11 and corresponding micro deflector elements in the micro deflec-tor sub-assembly
- 39 _
5 1 1
12. After passing througil the micro deflector sub-asseml~ly 12 there will be a.
multiplicit~ of essentially parallel electron beams all of ~lhich ~ill be de-
flected uniformly by the micro deflector 12 onto discrete areas of the electron
sensitive target membcr 910 Assuming, for example, that the micro lens array
provicles a matrix or array of lenslets numbering 128 by 128, then a correspond-
ing number of target areas will be traced on the electron sensitive target
member 91 within tlle scope of deflection of the respective micro deflection
elements and it becomes possible to uniformly control fabrication of up to 128
by 128 (15,384) microcircuit assemblies simultaneously.
Referring now to Figures 11-16 of the drawings, a different embodi-
ment o a micro lens array and micro deflector assembly is shown which is
somewhat different from the species of the invention described wi-th relation to
Figures 1-10. The Figures 11-16 species employs metal support rings and cup-
shaped outer supports for holding the ~arious sub-assemblies together in a
complete structureO In Figure 11, the micro lens array sub-assembly is shown
as comprising a pluralit~ of stackedl parallel, thin silicon plates 16, 17 and
18 fabricated in somewhat the same manner as described with relation to Figures
17 and 18 of the drawings. In the micro lens array shown in Figures 11-1~, the
required lens aperture (hole) profile as shown in Figure 17, can be obtained by
a variety of known photolithographic and etching techniques employed in the
fabrication of semiconductor integrated microcircuits. For exampleJ in a man-
ner similar to that shown in Figures 18A-18J,an N-type wafer of single crystal
silicon of approximately 1/2 millimeter thickness nnd 100 orientation has a
periodic oxide pattern produced on its two surfaces as sllown in Figure 18E.
The pattern is the negative of the desired hole pattern and is produced by well-
known oxidation and photo resist techniques~ The patterns on the two sides of
the silicon wafer may be the same size as shown but also may be different where
- 40 -
1~'75~
one is fa~ricating the end plates as illustrated in Figure 17. For end aper-
ture plates the slnaller holes are 0ssentially the required aperture diameter
~xhile the larger holes on the opposite side are made as large as practicable
without complctely ~mdercutting the underlying silicon supporting the aperture
during thc etching step. ~laving established the oxide pattern, a P~ dopant
material is diffused into the e~yosed surfaces of the silicon wafer by thermal
diffusion through the oxide mask as shown in Figure 18E. The wafer is then
etched using an orientation sensitive etch, for example, a hot pyrocathecol and
ethylene diamene bath, is employed so that diferential etching progresses from
the two sides o the undoped silicon as illustrated in Figures 18~1 and 18J. The
geometrically perfect outline of the aperture opening is determined by the
perfection of the crystal planes of the silicon which produces intersecting
square based pyrc~lids as sho~Yn in the combined views of Figures 18I and 18J.
Figure 18J is a plan view looking toward the bottom of Figure 18I and thus shows
the t~o circular boundary apertures 36 and 37 supported on the thin P~ boron
doped layer Wit~l the pyramidal opening in the intervening undoped N-type silicon
afer intersection to form essentially square-shaped openings in the center
of the thickness of the silicon waferO ~laving established the correct structure
for the aperture opening in the thin silicon plate, a coating of metal may then
be placed over the entire structure to make it conductive~ Any of the well-
known metalization tecimiques may be employed so long as there is adequate metal
to stop the electron beam completely. The method of ion plating identified
earlier in the "Electron Beam Techniques For Ion Plating" article and in the
"Physical Vapor Deposition" articlel are preferred because the plating metal
reaches internal surfaces and adheres wellO ~or a 10 kilovolt lens~ a thickness
of 2000 Angstrom units of heavy metal such as gold or platinum is adequate.
- 41 -
The key item for tlle ay~rtures is the profile of the small circular openings as
illustrated in ligure 17. The profile of the intervening underlying silicon
supp~rt is not criticalO The key factor then is the doped, thin surface layer
33 whicll defines and determines the areas of differential etching action for
production of the aperture openings and which must not be destroyed by the
etchant used in forming the aperture openings.
There are a variety of di~ferent, known ways in the art for accom-
plishing the above-described diferential etching action other than that des-
cribed earlier with relation to Figures 18A through 18J. For example, the thin
lq surface layer may be produced by epitaxial growth of a P~ layer on an N-type
silicon wafer. The hole structure is deined by ion implalltation of N-type
~aterial through an o~ide mask with holes where implantation is desired or by
thermal diffusion of N-type material through the holes. ~tching can then
follow in the same manner as described with relation to Figures 18A-18J. To
form the desired holes, since the form of the intervening supporting undoped
silicon is not critical, one could substitute an isotropic etch for the orien-
tation dependent etch in which case the silicon supports could follow a gener-
ally hemispherical outline rather than the pyramidal outline illustrated. In
producing the center lens plate 17 shown in Figure 17, a further restriction
2~ ~ust be observed in that the synmetry of the supporting intervening silicon must
be maintained with a high degree of accuracy due to the fact that the aperture
holes 36 and 37 on both sides of the plate are equal in diameter. Because the
orientation sensitive etching procedure described above maintains four-fold
symmetry of the intervening supporting silicon, it is preferred because it may
be so oriented as to correct the four-fold pattern of interaction bet~een
neighboring lenslets in an array of micro lenslets. By alternating orientation
- 4~ -
7 ~ 1 ~
sensitive etchill~ steps with other etching tec}miques, it is ~lso possible to
produce different configurations within the intervening supporting silicon but
of course the processing procedures become more complex requiring greater skill
and care in the fabrication.
In the embodiment of the invention shown in Figures 11-16J the
micro lens array is made as a stand-alone sub-~ssembly and for this purpose is
provided with top ancl bottom support rings as best shown in Figures 13 and 1
at 111 and 112, respectivelyO The support rings lll and 112 are thermally
bonded or otherwise secured to the axially extending glass support rods 19
lQ along l~ith the apertured thin silicon lens plates 16, 17 and 18 (and 18A if
provided) with the lower support ring 112 contacting and physically bracing the
lens plate 18A to prevent microphonics being induced therein by deflection
requency fields produced by the adjacellt micro cleflectoI sub-assembly. The
micro lens array sub-assembly shown in ~igures 13 and 14 then is mounted in the
overall assembly as best seen in Figures 11 and 12 by means of a central, annu-
lar cup-shaped mounting member 113~ This annular, cup-shaped mounting member
113 serves to hold the entire assembly together along with the termination plate
15 ~hich is secured to the outermost end portion of member 11~ with its aper-
ture openings axially aligned with corresponding apertures in the micro lens
array sub-assembly. Excitation potentials of about 5-10 kilovolts are supplied
to the inner thin silicon lens plate 17 by means of an insulator mounted con-
ductor connected by means of an intermediate conductor wire to the conductive
upper surface of the central lens plate 170 The end plates 16 and 18 can be
operated at essentially ground potential for the equipment and suitable lead-in
conductors to plates 16 and 18 are provided for this purpose.
The micro deflector sub-assembly employed in the embodiment of the
- 43 -
1157~11
invention shot~ in Figures 11 and 12 is best seen in Figures 15 and 16. In
this micro deflector sub-assembly, the ine deflector blades are made of
individual molybdenum blades which are sawed from a block of molybdenum or
alternatively~ individually blanked from sheet stock, and are stacked altern-
ately with spacers and then bonded together at thclr ends to ~lass support rods
114 and 115, respectively. The resulting sets of parallel, spaced-apart fine
deflector bars are provl~ed with elongated end bars as shown at 61A, 61B, 62A
and 62B, the elongated ends of which extend beyond the points of connec-tion to
the glass support rods 114 and 115, respectively. The elongated end portions
61A-62B are bra~ed or otherwise secured to an outer annular support ring 116 for
the micro deflector sub-assembly. As-best seen in Figure 11 of the drawings,
the outer support ring 116 is secured to the central annular cup-shaped mount-
ing member 113 for holding the micro deflector sub-assembly in spaced-apart,
parallel relationship with respect to the micro lens array sub-assembly wlth
the individual micro deflector elements of the sub-assembly axially aligned
with the individual lenslets apertwres of the micro lens array.
The complete fly's eye electron beam tube deflector/lens combination
is assembled by spot welding the mounting tabs from each of the micro lens
array and fine deflector sub-assemblies to the central, annularl cup-shaped
2~ mounting member 113. To assure proper registration and axial alignment of the
respective lenslets and MiCro deflector elements, 'tV" notches are placed in
the peripheral edge portion of the mounting rings and these are registered
against round alignment pins at each stage of fabrication and assembly starting
with the photo mask registration during fabrication of the thin apertured
silicon lens plates 16, 17 and 18~ The V notches and round alignnlent pins or
rods are best seen in Figure 12 at 117, llS, 119 and 1210 Figure 15 in con-
- 44 -
11~7511
junction with ~igure 12 illustrates the manner of connection of deflection
potentials to alternate ones of the sets of spaced-apart, parallel deflector
bars 61~1 and 6~1. Reerring to ~igure 15, the ~X deflection potential is
applied tilrougll a cross bar conductor 122 ~hich is spot welded to alternate
ones o tlle micro doflector blades or bars 62M and the -X deflection potential
is connected throug}l a conductor 123 to the remaining alternate ones of the
micro deflector bars 62hl. In a similar manner, the ~Y deflection potential is
connected through a cross bar type conductor 124 which is spot welded to the
tops of alternate ones of the micro de1ector bars 61M while the -Y deflection
lQ potential is connected through a cross bar conductor 125 spot ~Yelded to the top
of the remaining alternate ones of the de1ector bars 61M. By this construc-
tion, suitable deflection potentials are applied to all of the micro deflector
elements simultaneously for appropriate fine deflection of an electron beam
passing through any one of the elements as described previously.
During flnal assembly, the locating or alignment xods are held in
precisely macllined holes in the central annular cup-shaped mounting member 113
while assembly takes place. After spot welding the moun-ting ta~s of the micro
lens array and micro deflector sub-assemblies to the central mounting member,
the locating or alignment rods are removed otherwise they would give redundant
2~ constraints, and if metallic) would electrically short circuit certain of the
elements. It is also possible to obtain better alignment by use of electron
optical or light optical registration and alignment techniques instead of the
notches and alignment rods as described. As mentioned previously, to make the
micro lens array a stand-alone sub-asse~hly~ it was necessary to add two stiff-
ening rings which as indicated, are formed from molybdenum. It is also possible
to use metallic coated ceramic, metallic coated polycrystalline silicon, tungs-
- 45 -
~57511
ten, or metallic coated amorphous carbon. Of the metals, tungsten most closely
matches the thermal coefficient of expan~ion of silicon; however, for ultimate
thermal match, polycrystalline silicon having its surfaces metalized would be
the ~est. The polycrystalline silicon is preferred for use as a stiffening
member not only because it is cheaper to fabricate, but also it is stronger than
single crystal silicon which has a tendency towards easy fracture in certain
directions
In operation, the assembly shown in Figures 12-16 func~ions in pre-
cisely the same manner as the assembly described with relation to Figures 1~10.
~t should be noted, however, that because o~ the use of the rather massive cen-
tral, annular, cup-shaped mounting member 113, the arrangement Of Figures 11-16
requires the use of more metal tYhose temperature coefficient of expansion is
considerably differcnt from that of silicon and glass. Thus, creation of therm-
ally induced stresses are more likely to be encountered with the arrangement of
Figures 11-16 than is true with the assembly shown in Figures 1-10. For this
reason alone, the Figures 1-10 species is preferred but in addition, it is con-
siderably cheaper to manufacture and ligllter in weight also
Figure 2~E of the drawings illustrates an alternative form of micro
deflector sub-assembly construction which is different from that described with
relation to Figures 20-20D and the Fig-lre 1 and Figure 11 species of the inven-
tion. In Figure 20E a set of spaced-apart, parallel set in a block of silicon 66
having a through opening 66A shown in Figure 2~B and having slots 67 ~o accept
the deflector bars 614 This is achieved in much the same manne~ as described
ith relation to Figure 20C. However, in Figure 2~E the block 66 is made insula-
ting as by growing a silicon o~ide layer thereover~ and the deflector bars 61 are
permanently secured within the block of silicon 66 by means of glass frit or
thermal bonding as sho~Yn at 131. In a similar maTmer the metali~ed silicon de-
- 46 -
1 ls75~ l
flector bars 62 are permanently mounted in an insulating block 132 having a
physical configuration similar to that sholYn in Figure 20B but formed from
ceramic~ or silicon oxide coated silicon so that it is electrically insulating.
The metalized silicon deflector bars 62 aga.in are permanently secured in the
slots in block 132 by glass frit, thermal bonding or otherwise. De~lection
potentials are appliecl to alternate ones of the deflector bars 61 and 62 as
described previously through the conductors 133, 134, 135 and 136. The entire
assembly can be held together by thermally bonding the top sur:Eaces of the
second insulating block 32 to the lo~er edge portions of the deflector bars 61
and a suitable mounting ring secured thereto by mounting tabs as described
earlier whereby the structure can be mounted in assembled relationship adjacent
with a micro lens array sub-assembly similar to Figures 1 or 11. While the fine
micro deflector structure sho~m in Figure 20F~ has certain advantages~ it is ex-
pensive to fabricate in that the silicon and ceramic or oxide coated silicon
b.locks 66 and 132 are not reuseable and hence the design requires a substantial
amount of rather expensive materialO For this reasonJ the fine deflector struc-
ture shown in Figure 20D is preferred wherein the respective sets of ortho-
gonally arrayed deflector bars 61 and 62 are thermally bonded to transversely
extending glass support rods 68 at the ends thereof as described earlier~ The
blocksof silicon 66 having the slots 67 sawed therein then may be reused as
holding fixtures thereby economizing greatly from a material vie~point.
Figure 20F illustrates still another modified form of micro deflector
sub-assembly constructed according to the present invention. In Figure 20F the
orthogonally arrayed sets of spaced-apart, parallel micro deflector bars are
held in assembled relationship by respective glass support rods 68 extending at
right angles to the bars and connected thereto at respective ~ds of the bars as
described earlier with respect to the Figure 20D species of the invention. In
- 47 -
Figure 20~;, however, irl place o~ securing tlle nletallic elongated cnds of the en~
deflec*ion plates 61A, 61B, 62A and 62B to an annul~r support ring for secure-
ment to the axially extending main glass support rods 1~, the elon~ated ends
61A-62B are fabricated from a malleable material such as tungsten so that they
can be bcnt at substantially right angles,~to'directly contact and be thermally
bonded to axially extencling glass suppo~t rods 1~ in the manner shown in ~igure
2~ and in Figure 21. With the micro deflector sub-assembly secured to the main
axially extending glass suppor~ rods 14, the peripheral edges of thin silicon
lens plates 16, 17, lS and 18A ~if used) can be directly thermally bonded to the
axially extending main glass support rods 1~ as sho~n in Figures 21 and 21A.
The structure thus greatly simplified by the absence of the mounting rings~ is
completed by directly thermally bonding the peripheral edge of the target elec-
txode mPmber 13 to the axially extending main glass support rods 14 and the
termination plate 15 likewise is directly thermally bonded to the main glass
support rods 140 The assembly thus co~prised ~ay then be secured to the inner
peripheral edge of a suitable mounting ring support such as shown in Figure 25
for support within the housing or outer envelope of an electrode beam tube of
the fly's eye type. The resulting assembly would comprise essentially only
silicon and glass components and mini~izes to the greatest possible extent the
use of materials having temperature coefficients of expansion widely different
from those of silicon and glass. In addition to this rather substantial bene-
fit, the cost of the components is greatly reduced as is the cost of their pro-
cessing not to mention the reduction in ~eight and ability to minimize the size
of the entire assembly,
In the effort to miniaturize the si~e of the combined micro lens
array and micro deflector assembly in the manner depicted in Figure 21 and Figure
21A of the drawings, the physical spacing between the thin, apertured silicon
lens plates 16, 17 and 18 can be become critical~ In order to overcome
- ~8 -
5 1 ~
this problem, and still at the same time insure an adequate alnount of insulator
between adjacent edges of the spaced-apart lens plates whereby they will be
able to withstand substantial potential differences of the order of 5-lO kilo-
volts or perhaps even greater, the plates can be mounted to modified glass
support rods as sholYn in Fi~lres 22 and 22A o-~ the dra~Ylngs In each of these
Figures the glass support rods are provided with suitable in~ardly extending
projections wnich contac~ the peripheral edge portions of the silicon plates at
the point of thermal bonding whereby the effective insulator distance between
adjacent silicon plates can be made ~o be much greater than the plate separa-
tion distance. For this purpose, the a.~ially extending, main glass support rods5uch as 14A in Figure 22 are provided with inwardly extending branches 137. As
an alternative, the main axially e~tending glass support rods, such as l~B in
Figure 22A, may be bowed outwardly as shown at 138 for the extent thereof cor-
responding to the space between adjacent lens plates.
Figures 23 and 23A of the drawings illustrate another alternative
method of securing together the orthogonally disposed, metalized silicon micro
deflector bars 61 cmd 62 having the ends thereof secured to glass support rods
68A and 68B, respecti~ely, as described previously. In Figure 23 and Figure 23A,
the glass support rocds 68A and 68B to ~Yhich the respective ends of the micro
deflector bars 61, 62 are thermally bondecl, are extended sufficiently so that
they intersect one over the other and are thermally bondecl together at the
point of intersection. A small, insulating, sapphire ball shown at 139 may be
interpo~ed and thermally bonded to the intersecting glass support rods 68A and
68R at the points of intersection to adjust the spacing bet~Yeen the sets of
deflector bars. With the construction sholYn in Figures 23 and 23A, it is
possible to get the closest possible spacing bet~Yeen the orthogonally disposed
- 49 -
11575~ ~
metalizecl silicon deflector bars ~1, 62 without requiring the need for elon~
gated, metal end cleflector bars as discussed in earlier descri~ed arrangements.
To mount the micro deflector sub-assembly, the ~lass support rods 68A and 6~B
may be e~tended sufficiently to allo~Y one or both to be secured to a mounting
ring. Alternatively, an axially e~tending glass rod 14 can bc directly therm-
ally bonded to the intersection of 68A and 68B for mounting within an electron
beam tube as indicated by dotted lines at 14 in Figure 23.
As described earlier with respect to Figure l and Figure 11 species
of the invention, for holding the ~icro lens array and micro deflector assem-
bly together or for mounting the assembly in a fly's eye electron beam tubestructure, one may use any of the standard fastening means such as spot welding,
brazing or even bolting together, all of which have been used in prior art
devices. For e~c~lple, it is not unusual to use a combination of machine screws
and spot welding for assembly.
Spot welding the component parts of a fly's eye electron beam tube
has disadvantages in that it is limited to joining conducting materials. Thus
for joining silicon and ceramics or glass, an additional step of providing
~ounting tabs or flanges is required. Spot welding also creates debris and is
not suited to ready disassembly for realignment or replacement of component
parts. Additionally, spot welding segregates alloys, causing instability and
magnetic combinations to be formed during the spot welding procedure in nearby
metal parts that are magnetizable. Finally, spot welding produces stretching
at certain points of the metal parts being joined thereby resulting in distor-
tion and leaves rough surfaces which can cause corona and arc-over during oper-
ation of the electron beam tube.
~razing of the sub-assemblies together for mounting the resulting
- 50 ~
115751~
micro lens and micro deflector assembly within the electron beam tube has dis-
advantages in that it requires complex ixturing to maintain alignment through
a high temperature cycle required to braz~ the parts together. ~dditionally,
the brazing process may require flu.~es ~hich are difficult to remove after the
bra~ing operation on order to make the assembly electron optically clean. It
is difficult to retain the brazed iller at the desired locations where join-
tures are ~o be accomplished and finally, the resulting structures cannot be
readily disassembled non-destructively.
Bolting or assembly through machine screws has disadvantages in that
the bolts or screws generally are conductors and thus require complex insulator
sleeving, spacers, etc. to avoid shorting out different parts of the assembly.
Tightening of the bolts or machine screws tends to force the assembly out of
alignment just as it approaches final position unless very elaborate means are
employed through co~plex and bulky clamps and fixturing to separate the clamp-
ing force from the rotation ~Yhich produces the orceO Additionally, available
screws and bolts have thermal coefficients of expansion which are not close
enough to the coefficient of expansion of silicon and ceramic insulators to
maintain the assembly integrated throughout the bake-out cycle. To produce
screws and machine bolts of special materials such as tungsten in order to over-
2q come this problem, removes the cost advantage of using bolts and screws in thefirst place.
In the products herein described, glass rodding as a m~ans for
assembling the various component parts together into sub-assemblies and there-
after joining the sub-assemblies into a complete assembly, is preferred since
the cost and integrity of the resulting structures are quite acceptable and the
techniques for glass rodding well known and proven. In the case of fa~lty
1~751~
assembly, by "cracking the glass" the expensive parts of the assembly such as
the thin silicon lens plates ancl micro deflector bars generally can be reclaimed.
Since the glass rodding is no~ too expensive, this method of disassembly is
acceptable for realigllment and replacement problems.
~s noted in thc preceding paragraph~ the glass rodding technique of
assembly does not lend itself readily to easy nondestructive disassembly. In
those applications for a fly~s eye electron beam tube where disassembly is a
key factor, as for exa~ple in use o the fly's eye electron beam tube for art
work generation in the Xabrication of microcircuits, and the like, an assembly
method employing precision sapphire balls mounted in conical recesses can be
employed. This basic method oÇ assembly is disclosed in Figures 24J 24A, 26,
26A, 26B and 27 of the drawings As may be expected, the thin, apertured sili-
con lens plates arc too brittle to be clamped between precision sapphire balls
without taking special steps to accommodate this technique of assembly. As
shown in ~igure 24, one procedure is to fuse the peripheral edges o the thin
silicon lens plates such as 16, 17 and 18 to axially extending glass rods 14.
The micro lens array sub-assembly thus comprised can then be separately mounted
on a mounting ring such as shown at 141 in which circular openings 142 are
~ormed. A small insulating sapphire ball 143 is inserted in the hole or opening
142 in mounting ring 141 and the end of the supporting glass rod then thermally
shaped to form sockets for seating the insulating sapphire balls 143. Figure
24A of the drawings illustrates a technique for fabrication of the structure
sho~n in Figure 24 using a vacuum chuck and gas flame to heat the glass support
rods 14 to approaching their melting temperature~ The thin, apertured silicon
lens plates 16~ 17 and 18 are then pressed into engagement with the glass sup-
port rod 14 by suitable holders ~not shown) and either concurrently or sequen-
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tially, the insulating sapphire balls moull-ted in suitable holders 145 and 146
are brought into engagement with the heatcd ends o the glass support rods 14
to simply press a ball seat in the ends of the glass rods. The glass support
rods 14 cool slowly eno~gh to permit orming the ball sockets all in one oper-
tion immediately ater pushing the glass support rod into proper mounting posi-
tion with relation to the balls and ~hin silicon plates 16-18. The sequence
of operations are 1~ the glass rod 14 is moved to the right to engage the ends
of the thin apertured silicon lens pla~es 16, 17 and 18 after being heated by
the gas flame. Downward motion of ~he sapphi~e ball holder 145 and upward mo-
tion of the sapphire bali holder 146 indicated as motions 3 and 6 may occur
~imultaneausly with motion 1 ~ith these motions being sequentially followed by
motions 2, 4 and 5 to ~ithdra~ the urnace and holders from the glass rodded
sub-assembly shown in Figure 2~o The resulting structure then is mounted as
shown in ~igure 24 on mounting ring 141 having apertures 142 for receiving the
small insulating sapphire balls 143~ In place of using the gas flame heating,
one could use heating methods employing electron heat fusion, laser heat fusion
or radio frequency heating of the glass rod prior to pressing the thin apertured
s.ilicon lens plate and sapphire balls into position on the rods. The inexpen-
sive, artiicial sapphire spheres used as the insulating balls 143 are ideal
as forming tools for fabri.cation in accordance with this technique.
Figure 25 illustrates a preferred method for attaching a flange to a
c~arse deflector cone for electron beam tubes of the fly's eye type wherein the
coarse deflector cone 90 has the coarse deflector electrode 102 formed thereon
by any suitable known metalization glass technique~ The ends of the coarse
deflector cone 90 on the outer surfaces thereof are shaped to receive and coact
with a metal mounting band 147 having an outwardly extending flange portion 14~
1~$'7~11
to ~Yhicil are secured suitable glass rod nlo~lnting tabs such as ~6, 88 and 90
described with relation to Figure 1 of the drawings, The flanged metal band
147, 148 is secured to the ends of thc glass tu~e envelope 90 by heat shrink-
ing the band 147 over the end o the glass tube. The metal band 147, 148 may
be prefinished in advance of the heat shrinking process, or alternatively may
be finished after securement to the sides of the glass tube. The structure
shown in ~igure 24 may be mounted on a mounting flange similar to that shown in
Figure 25 and which corresponds to the mounting ring 141 shown in Figure 24.
~o heat the metal band 147, it could be heated with radio fre~uency electric
fields or electron, or laser beam heating as well as by a gas fired furnace
while the glass enYelope 90 of the tube is maintained substantially at normal
room or ambient temperature, The dimensions of the metal band 147 are propor-
tioned so that upon being heated it can just be slipped over the end of the
tube glass en~elope ~4 and upon cooling will shrink it to a tight bond.
~igures 26, 26A and 26B illustrate still other forms of the inven-
tion for use in fly's eye electron beam tubes of the type that must be easily
broken do~m and taken apart for operational useO In the embodiment sho~m in
Figure 26, the central thin apertured silicon lens plate 17 is provided with a
set of relatively thick pads shown at 151 and 152 secured on both sides of an
outer peripheral edge po$tion thereof. ~ach of the pads 151 and 152 has a
pyramidal or conical shaped opening indicated at 153 formed therein for recei~-
ing and seating a small, insulating sapphire ball such as sho~n at 143 and 143A.The sapphire ball 143 itself is seated in a circular opening formed in the
peripheral edge portion of one of the outer thin apertured silicon lens plates
1~. The sapphire ball 143 also seats in a pyramidal or conical shaped cavi~y
153 in a thick pad 154 secured to a peripheral edge portion of the termination
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5 1 1
plate indicated at 15. Ihe sapphire ball 1~3A is designed to seat in the
pyl~amidal or conical opening 153 formed in the lower pad 152 and in turn seats
in an opening formed in the peripheral edge of the lower thin apertured silicon
lens plate 18. Tlle lower end of the lower insulating sapphire ball 143A in
turn is seated in a circular opening in the annular mo-mting ring member 87 of
a micro deflector sub-assembly 12 ~Yhich may be fabricated as described with
relation to Flgure 1 of the drawings. The entire assembly including the termin~
ation plate 15 and mounting ring 87 may Lhen be supported within an evacuated
electron beam tube housing in a manner to be described hereinafter with respect
to Figure 27, for example. Thus, it will be appreciated that with the arrange-
ment of Figure 26, disassembly of the components of the micro lens array for
realignment purposes, etc. is facilitated ~rithout requiring breakage of glass
support rods,or the likeO
Figures 26A and 26B illustrate modified constructions or the insert
ashers to be placed between the thin apertured silicon lens plates in order to
control the spacing distance between plates and at the same time provide an
adequate thickness to facilitate use of the small sapphire balls employed in
assembling the elements in a composite structure such as sho~ in Figure 26.
In Figure 26A the insert is shown as a relatively thick, flat annular washer
type of spacer 155 having a central opening of sufficient dimension to accommo-
date the ends of the small sapphire insulating spacer balls 143. In the Figure
26B species, the additional washer-like spacer 156 is provided with rimmed
edge portions to accommodate the peripheral surfaces of openings formed in the
thin apertured silicon lens plates. In each of these species, if the lens
plates to be spaced apart are to be maintained at di~ferent potentials, the
spacers 155 and 156 would be fabricated from electrical insulating material
5 1 t
such as glass> alumi~ o~ide or silicon dioxide coated silicon or other
similar compatible m,ltcrial. If the adjacent plates shown wlth the end of the
coarse dcflcctor cone 90 terminating in a shrink fitted metal mounting flange
147 havillg c~n outwardly extending rim 148 cons~ructed according to Figurc 25
o~ the clra~lngs. 'rhe rim 1~8 o~ mountillg flange 1~7 has a lip which receives
and seats the tcrmination plate 15 having ball seats formed therein for accommo-dating alignment balls 143 for seating an~ supporting the lower ends of the
support rods 14 for the micro lens array 11~ The micro lens array 11 may be
fabricated as showll in Figure 24 of the drawings and has its upper sapphire
balls seating and supporting the lower ends of the axially extending glass sup-
port rod 14 of a micro deflector 12 constructed as described ~ith relation to
Figure 23 o the drawings. An alignment ball 143 seatecl on the top of the
axially e~tending glass support rods 14 o the micro deflector in turn is seatedin the pyramidal shaped opening of a set of spacer pads 151 and 152 are spaced
on either side of the target electrode member 13 in a manner similar to that.
described with relation to Figure 26~ ~he spacer ball 143 seated in the opening
on the top of the spacer pad 151 in turn seats in an opening in an annular com-
pression plate 157 that may comprise an integral part of the end cap structure
158 for the array optics assembly. The combined end cap and compression plate
157, 158 is provided with an outer mounting flange 159 having openings therein
that form seats for the aligmnent sapphire spheres 143~ ~he entire structure
comprising compression plate 157, end cap 158 and mounting flange 159 may be
fabricated from glass or an electron optically clean metal such as tungsten or
molybdenum, ceramic or other suitable material having the required impervious-
ness to gases and structural rigidity. Mounting flange 15~ has a grooved sur-
face around its outer periphery in ~Yhich the sapphire balls 160 seat in the
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5 1 1
upper flange 161 o~ an outer housing envelope member 162 for the micro lens
array and micro deflector assembly. tlousing member 162 also has a lower mount-
ing flange 163 coacting with the rim porti~n 1~8 o~ metal band 1~7 to seat and
support the assembly on sapphire balls. 16~ ~he mounting ~langes 159 and 161
ancl 163 and 148 are compressed together against the sapphire balls 160 and 16
by a set of Inconel steel compression springs shown at 165 inserted by means o~
a loading tool 166. After insertion with the loading tool, the clamping sprin~s
165 rigidly hold the entire structure in assembled relationshipO
As an alternative to the arrangement shown in Figure 27, where the
intended application of the fly's eyeJ electron beam tube does not require ready
disassembly for changing target members 13, such as where the intended applica-
tion is for use as an electron beam accessible computer memory, the combined
micro lens array ancl micro deflector assembly including target member 13 shown
in Figure 21 of the drawings could be inserted bodily in place of the three
part assembly comprised by sub-assemblies 11, 12 and 13 of Figure 27. With such
an arrangement, the ends of the axially extending glass support rods 1~ shown in
Figure 21 would be compressed to receive the alignment balls 1~3 employed in
mounting the micro lens array and micro deflector assembly between compression
plate 157 and termination plate 15 of the structure shown in Figure 27. Need-
less to say, the termination plate arrangement 15 illustrated in Figure 21would not be required in any such modification since it would be redundant in
view of the use o~ the plate 15 as a compression member in the modified Figure
27 structureO
The technique and apparatus for fabricating thin, apertured silicon
lens plates for micro lens arrays according to the invention lend itself to
improved methods for reduction of third order spherical aberration of the lens
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1 ~5 ~51 1
(which varies as the cube of the lens aperture in radius or angle). It has
been established that third order aberrations in electron lenses can be correct-
ed by one of three methods: 1) Use of some ~mround apertures, 2) Place a
source of charg~ near the lens axis, 3) ~ary the lens power with time.
The last met}lod described in (3) above requires impracticably high
rates of variation. The second method described in (2) becomes progressively
less attractive as the beam energy is reduced and is best suited to electron
beam energies above 30 kilovolts. The unround aperture technique described in
(1) is the most attractive since it will ~ork at any voltage and is not res-
tricted in use to higller beam energies. ~he double, thin conducting film cross-
sectional con~iguration of the silicon lens plates 16, 17 and 18, as well adapted
to the formation o unround lens apertures on elther side of the plates as best
illustrated in Figures 28 and 28A of the drawings. Referring to Figure 28, an
upper silicon lens plate 16 is fabricated with a small diameter circular aper-
ture 171 formed in its upper surface and an elliptical or semi-elliptical aper-
ture 172 formed in its lower conducting surfaceO When viewed from below, the
plane of the lens plate would then appear as shown in Figure 28 to provide the
unround aperture openings 172 for correction of the undesired third order
aberrationsO The unround ~elliptical or semi-elliptical) openings 172 may of
course be fabricated by appropriate design of the photo-resist pattern employed
in defining the undoped silicon surfaces to be etched by the etchant as des-
cribed previously with respect to Figures 18A-18J of the drawings. Figure 2~
is a cross-sectional view through one of the unround apertures sho~n in Figure 28.
An additional advantage of fabricating the thin lens plates as shown in Figures
28 and 2~ is that by use of such unround apertures, the number of plates that
will be required in the stacked, parallel array of lens plates possibly can be
reduced, perhaps by a factor of 2.
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1 1 5 '~
In the embodiments of the invention described abov~, it should be
understood that the thin conductive layer 33 on each side of the thin, apertured
silicon lens plates ~for dual-sided lens plates~ or on the single side of the
extrelnely thln lens plates ~as shotYn in Pigures 30 and 31 to be described here-
after) may comp~ise the highly conductive doped layer of silicon resulting from
the processing of the starting silicon wafer without requiring that a further
conductive coating or metalized layer of platinum~ gold, silver or other heavy
metal be disposed over the remaining surfaces of the thin, apertured silicon
lens plates. Further, while the invention llas been described primarily with
relation to assem~lies employing 3 or ~ lens platesJ it is not limited to such
structures. Figure 29 of the drawings illustrates the preferred axial profile
of a single channel of a micro lens array sub-assembly according to the inven-
tion ~hich employs five (5) lens plates in the stacked array-of parallel lens
plates. In Figure 29 the top plate 16 has the large diameter opening 32 in the
highly conductive boron doped layer 33 exposed to the incoming electron beam
with the smaller diameter beam limiting aperture 31 being located on the exit
side of the plate. A second inlet lens plate 16A of similar construction is
arranged in the same manner as 16. The center plate 17 to which the high foc-
using potential is applied has equal diameter apertures 36 and 37 formed on
~Q opposite sides thereof in the same manner as described with relation to Figure
17. The t~o exit plates 18 and 18A have the small diameter limiting apertures
31 disposed on the upper surfaces thereof that are exposed to the incoming elec-
tron beam and the larger diameter apertures 32 are located on the beam exit
side of the platesO
~ igures 3~ and 31 illustrate a some~hat different cross-sectio~al
configuration for the lens plates of the micro lens array ~hereby extremely fine
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11~'751~
spacing betwcen the plates can be obtained. 'rho starting material is a waEer
181 of single cry~talline silicon having a diameter of about 7-9 centimeters
and a thickness of 1/2 millimeters. 'rhe wafer 181 is processed in a manner
similar to the method described with rela-tion to Figures 18A-18J using quite
dif~`erent maskil-g patterns for the t~Yo sides of the wafer. On one side ~which
may be the upper side exposed to the incoming electron beam~ a comparatively
large rectangular opening 182 is left open to the action of ~he etchan-t and an
array of fine aperture openings 31 having diameters of the order of one to
two microns ~1-2~) is formed in the lower boron doped surface 33 of the wafer.
The boron doped surface extends around the edges and over a substantial upper
peripheral portion of the wafer as shown at 183 to provide sufficient rigidity
and strength for mounting the resulting lens plate. Etching action through the
top surface opening 182 is allowed to proceed all the way through the thickness
of the wafer to the lower boron doped layer 33 defining the lens apertures 31.
This action results in the formation of the tapered shoulders 184 exténding be-
tl~een the matrix of apertures 31 on the lo\Yer surface and the upper peripheral
portion 1~3. ~he resulting lens plate in the active area of the electron beam
~ay have a thickness of the order of one to two microns (1-~) while defining
lens apertures having diameters of the order of one to t~Yo microns ~1-2~) each
2~ thereby maximizing to the greatest possible extent the number of data bearing
chanllels that can be designed into an electron beam accessed memory tube. The
iens plate construction sho~yn in Figures 3~ and 31 could be used in any of the
micro lens array sub-assemblies described in the preceding portions of the spec-
- ification and even makes possible the design of practical assemblies employing
only a single ~icro lens plate as the ~icro lens array sub-assembly. In such
constructions, only the single lens plate shown in Figures 3~ and 31 ~ould be
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5 ~ 1
inserted for the micro lens sub-assembly 11 employed in the struc-tures of
Figures 1, 11, 21, 2~, etc~ Nhile it might be possible to use a single lens
plate fabricated as described with relation to plate 16 in Figures 18A-i8J
of the drawings as a micro lens array sub-assembly, the construction of Figures
30 and 31 is preferred fox single lens plate structures.
From the foregoing description, it will be appreciat~d that the per-
fection of the silicon e~ching symmetry and the precise geometrical control in
three dimensions which is made possible by the boron diffusion and pyrocatechol
and ethylene diamine etching action to limit the etching to predetermined loca-
tions, makes possible the fabrication of dramatically new and different lensplates for use on micro lens array elements. The steps in the preferred method
Q lens plate production are shown in Figure 18 o tlle drawings~ The technique
employed makes possible the fabrication of two-layer structures where the aper-
ture formed on one side of the lens plate has a different configuration from
the aperture forlned on the other, as described with relation to Figure 28.
Pifferent shaped apertures "piggy backed" on a single lens plate have been tried
previously with photoetched metal plates~ The problems encountered, howeverJ
were that the thin metal plates were not providing sufficiently round holes,
were not staying in plane and (being of a differen-t metal in order to give
~0 selective etching cllaracteristics~ was also a bi-metallic plate subject to
thermal warping. The doped silicon lens plates provide differential etching
capability whereby different shaped apertures can be formed on opposite sides
of the plate without introducing bi-thermal properties. Furthermore, where the
apertured different configurations are "piggybacked" on the single lens plate,
it is difficult to make the plate thick enough to cause the aperture to be
placed outside the fringe field of the lens. Using boron doping and differen-
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tial etching fo~ defini~ion of the aperturc openingJ suf~ici~ntly high quality
holes can be formed on A "piggybacked" structure to make their use practical
whereby fewer lens plates may be required in place of a larger number usually
required in micro lens arrays abricated from metal plates. This is made poss-
ible because control of the positioning of the aperture openings, their symm-
etry and size is of an order of magnitude improved over prior kno~n construc-
tions.
It should also be noted that in the fabrication of the micro d~flec-
tor assembly, the fine micro deflector bars or blades are sawed from a solid
1~ block of silicon and the resulting blades or bars subsequently metalized. This
procedure also is true for blades made from aluminum oxide ceramic or vitreous
carbon as a starting material. Needless to say, the sawing oE the individual
blades and subsequent metalization of the blades requires individual processing
of these parts and hence increases the cost of the micro deflector sub-assembly.
For very large volume use, the cost per fine deflector unit can be reduced and
the advantages of unitary construction achieved, i.e., pure materials, no ba~e-
out limitations, stress free, and no vacuum pockets, by pyrolytic formation of
polycrystalline silicon from halogen ~apor into a graphite master mold conform-
ing to the desired micro deflector sub-assembly sets of bladed structures. The
2~ process of such pyrolytic silicon formation of large complex objects is well
established in the manufacture of polycrystalline silicon furnace tubes and
furnace boats as described in the article entitled "The Preparation and Proper-
ties of CVD-Silicon Tubes and Boats for Semiconductor Device Technology",
Journal of the Electrochemical Society, ~olume 121 (1974), page, 112-115, by
~, ~ietnze, L.P. Hunt and D.H. Sawyer. Thus, for large volume fabrication of
the fine deflector sub-assemblies, in place of sa~ing out the individual blades
- 62 -
1 ~5'7~ 1 1
and mounting thcm in two separate sets of interdigited, orthogonally arrayed,
spaced-apart parallel bars as described above, four individual sets of bars can
be fabricated initially from a master molcl as described in the above-referenced
article Two sets may then be interdigited and mounted for x axis deflection
ancl tlle remaining -~wo sets interdigited and mounted for y axis deflection. The
two sets of interdigited bars produced by the polycrystalline silicon then are
arrayed at right angles to each other and alternate ones of the interdigited
sets of bars appropriately interconnected electrically to operate in the pre-
viously described nlanner to provide -x, ~x and -y, ~y deflection.
HaYing described several embodiments of a new and improved micro lens
array and micro deflector assembly for 1y's eye type electron beam tubes con-
structed according to *he invention~ it is believed obvious that other modifi-
cations, variations and changes in the i~lvention will be suggested to those
skilled in the art in the light of the above teachings. It is thereore to be
understood that changes may be made in the particular embodiments of the inven-
tion described which are wi*hin the ull intended scope of the invention as
defined by the appended claims.
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