Note: Descriptions are shown in the official language in which they were submitted.
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This application is a division of Canadian application
Serial No. 249,523 filed April 5, 1976.
BACKGROUND OF THE INVENTION
The present invention relates to the general subject
of electron optical systems and more particularly to such systems
wherein a beam of corpuscular particles is scanned over a
selected area of a specimen and the electrical signal derived
therefrom is displayed upon a television type monitor (raster
driven cathode ray tube).
With the development of electron microprobes systems
having a beam of sufficiently high brightness (content of energy)
so that high speed scanning of a specimen surface, e.g. scanning
at rates comparable to those exhibited by commercial television
systems, "Real Time" Scanning Electron Microscopes having high
magnification viewable on TV screen~ have become a commercial
reality. With the advent of such "TV-linked" systems have come
a number of changes in the style and practice of electron micro-
scopy. Now, an electron beam, having a high concentration of
electrons, can be finely focussed (to a spot diameter of a few
2~ Angstroms), and caused to scan a specimen surface in synchronism
with the electron beam of a CRT monitor.
The impact of the electron beam upon the specimen
within the microscope can be detected by any of a variety of
devices (x-ray detectors, backscattered electron detectors,
etc.) and the signal of such device used to modulate the brightness
of the TV tube beam. In the case of the very high brightness
sources for electron beams (field emission tips) sufficient
signal to noise level can be maintained such that even at very
high magnification (50,000X or more) a real time, TV rate scan
and display may be enjoyed. Scientists and researchers have
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found tremcndou~ ~dvanta~e ln beln~ ~ble to lm~edistely
vlew on a TV screen a hlghly magnlfied ~peclmen surface, to
compare and select ehe areas of relatlve lnterest, and the
determlnation of ~uitable slght~ for photomlcrographs. As the
lnterest in highly magnifled speclmen examinatlon forces hlgher
resolutlon of photomicrographs, advantages of the developments
withln the TV lndustry have become available as buildlng blocks
for further advance ln state of the art of Field Emission
microscopy. For example, as TV monitors having hlgher resolution
(higher numbers of lines) and a variety of times of persistence
phosphors have become available, the scan of the electron beam
on the specimen has still been synchronizable with the TV type
monitor, wlth the result of improvements in the performance
of the total system. For example, specimen scanning rasters of
lOOO line and 2500 lines are common, with additionally select-
able, variable interlace patterns, either sequential or non-
sequential, depending upon the particular advantages sought from
the system. (See, for example, U.S. Patents 3,767,926 (Re.28153)
and 4,047,204 issued October 23, 1973 ~September 10, 1974) and
September 6, 1977 to V.J. Coates and L.M. Welter).
It has also been determined that a variety of additional
information may be gained from a specimèn if, while scanning
the specimen for response in a particular response (e.g. angle
of beam impingent, secondly, backscattered electron detector,
~-ray mapping) and direct comparlson with a collateral specimen
response tSUch as above, or scanning transmission bombardment)
additlonal information might be gained from the specimen. The
billty of the fleld emission microprobe system to respond with
real time response lends additional advantages
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to the above investigations - particularly for simultaneous
comparative viewing such as in a stereoscoptive type of pre-
sentation.
The present invention is an improvement o~ an electron
optical system adapted to a TV type imaging device and synch-
ronized in raster pattern to the system electron probe.
The present system finds particular advantage in such
systems as those in which two immediate images need to be com-
pared such that simultaneous viewing gives the viewer information
beyond that available from single images. Particularly, in
those situations where separate images of an object are formed
such that when these are viewed in particular relation, stereopsis
may be observed, the viewer gains depth information which cannot
be obtained from the single image. The current development of
the electron microscope art is such that separate, coordinated
photomicrographs may be prepared and later compared in suitable
viewing device such that the stereoptic information can be ex-
tracted. Considerable re earch efforts have been expended in
recent years toward the development of a "real time" stereo
capability in a high magnification electron microscope. Realtime systems capable of operation in lower magnifications (2000X)
have been achieved with multicolor systems or with comparatively
low resolution.
It is not until the present advance that a high
resolution, high magnification scanning electron microscope has
become available which could be developed as a satisfactory
industrial or research quality instrument.
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In addition the present invention offers the flexi-
bility of an electron microscope which allows the simultaneous
viewing of an image which is formed from the different returns
of two electron detectors. Specific examples may include the
viewing of a backscattered electron image with a secondary
electron image, in side-by-side relation and simultaneously.
It is thus one of the several objects of the present
invention to provide such simultaneous viewing of two images of
the same selected surface area of sample, however simultan-
eously producing separate images, carrying different informationsuch that direct comparison may be made of the images with the
as~urance that the same specific surface of the specimen is
being viewed.
S1~5MARY OF THE I~VENTION
In accordance with certain features of the present
invention, a scanning electron microprobe and display system is
disclosed which is adaptable to stereoscoptic or side-by-side
image comparison on a television type monitor. The apparatus
includes means for scanning the microprobe beam in a raster over
a specimen and displaying the Lmage on the cathode ray tube (CRT)
viewer. Additionally, the microprobe beam scan is synchronized
to the beam of the CRT and the CRT horizontal scan is blanked
over a portion of its extent for sequential fields. For stereo
viewing, the angle of incidence of the microprobe is varied in
relation to the blanking sequence to provide side-by-side images
on the CRT, which are generated from different microprobe incid-
ence angles. The thus generated side-by-side images may be
viewed with a stereo viewer or other means for the stereoptic
effect.
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The lnvention according to the parent appllcation
provldes ln a scanning charged particle microprobe system lnclud-
lng a source of charged partlcles, means for colllmatlng the
partlcles lnto a beam, means for scanning the beam ln a pre-
determlned raster pattern over a specimen ln the mlcroprobe
system, detector means lncluding means for generating a slgnal
proportional to charged particles detected, CRT lmage recordlng
means connected to the detector means to record detectlon of
charged particles exltlng the specimen, the improvement comprlsing
means synchronizing scan of beam of microprobe to the beam of
the CRT; means for blanking a first predetermined portion of such
horizontal sweep of the CRT beam scan for a first field of the
scan; means for causing the beam of the microprobe to scan
specimen at a first predetermined average angle of incidence for
the first field of CRT beam blanking; means for blanking a second
predetermined portion of each horizontal sweep of the CRT beam
scan for a second field of scan; and means for causing the beam
of the microprobe to scan the specimen at a second predetermined
average angle of lncidence for the second field of CRT beam
blanking, at least a portion of the horizontal sweep of the second
field blanking being mutually distinct from a part of the
horizontal sweep of the first field blanking, whereby side-by-side
images responsive to the sweep of the microprobe are produced on
the CRT.
On the other hand the invention according to the present
application provides in a scanning charged particle microprobe
sy8tem including a source of charged particles, means for collimat-
ing the particles into a beam, means for scanning the beam in a
predetermined raster pattern over a specimen in the microprobe
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system, detector means lncludlng means for generatlng a signal
proportlonal to charged particles detected, CRT image recordlng
means connected to the detector means to record detectlon of
charged particles exiting the specimen, the improvement compris-
ing: means synchronizing scan of beam of mlcroprobe to the beam
of the CRT; means for blanking a first predetermined portion of
such horizontal sweep of the CRT beam scan for one field of the
scan; means for blanking a second predetermined portion of each
horizontal sweep of the CRT beam scan for a second field of scan;
means for detecting charged particles emitted by the specimen
in response to impingement of the beam on the specimen; means for
detecting a predetermined class of charged particles and record-
ing the detection of the particles on the CRT during the first
blanked field; and means for detecting a second predetermined
class of charged particles and recording the detection of the
particles on the CRT during the second blanked field, whereby
side-by-side images representative of two classes of charged
particle emission of a single area of the specimen are displayed
on a CRT image recorder.
DESCRIPTION OF THE DRAWINGS
The invention described herein is additionally
illustrated in the attached drawings in which:
Figure 1 is a block diagram of an embodiment of the
invention for stereoptic viewing.
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Plgure 2 1~ n block dlagram of an e~bodlment of the
lnventlon lllustrated in Flgure 1 adapted to a scannlng electron
microprobe ~ystem.
Flgures 2a and 2b are diagrammatlcal ray vlews of the
stereo eye viewer of Flgure 1.
Figures 3a and 3b are ray dlagrams of the microprobe
beam scanning system according to the lnvent$on.
Figures 3a' and 3b' are illustrations of the v$ew on
the viewing screen for the ray patterns of ray diagrams of Figures
3a and 3b.
Figures 4a-4d are views illustrative of phase shifting
ant synchronizing signals used for beam blanking and the formation
of the composite stereo vie~.
~ igure 5 is a schematic diagram of control circuitry
for the invention of Figure 1.
DESCRIPTION OF A PREFERRED EMBODIMENT
For an understanding of the operation of an electron
~icroscope within which the present invention ma~ be observed,
reference may be had to one of the several patents issued which
are owned by the assignee of the present invention. Among these
are U.S. Patents 3,678,333 (July 18, 1972~; 3,766,427 (October 16,
1973); 3,767,926 (October 23, 1973); re 287153 (September 10,
1974); 3,784,815 (January 18, 1974) to Coates and Welter and
3,842,272 (October 15, 1974) to Coates, Welter and Gold. From
uch as these references it may
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be seen that a beam of electrons is produced by a source, which
is indicated by reference numeral 10 on Figure 1, which in these
preferred embodiments is a field emission electron gun. The
beam is directed upon a specimen 12 to be observed in a focused
condition by focusing coils 14. The beam is scanned in a
television type raster format by a deflection system 16; all of
the foregoing being illustrated in the aforementioned references.
Impingement of the electron beam upon the sample causes a
variety of responsive emissions by the sample, depending in
part upon the energy level of the impinging beam. In the illus-
trative embodiments where the beam energy is in the range ofa few to tens of kilovolts (eg, 5 to 20k~) the responsive
emissions may include secondary, backscattered and reflective
electrons. X-Rays and ions may also be emitted depending upon
beam energy and density. These are conventionally collected
by a scintillation type detector 18 and routed to a signal
amplifier 20 which, in turn, becomes the input to the television
type monitor 22.
Prior to the present invention, only a single type of
the responsive electrons could be collected at any one time and
displayed in image form on a single monitor. As will be
explained below, the present invention allows the simultaneous
viewing of several types of these responsive electrons, such
that two or more images may be simultaneously analyzed.
Referring back to the monitor 22, the writing beam
of this cathode ray tube device is synchronized and phased to
the raster of the deflection system 16 to ensure that each
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specific line of scan of the observed specimen is coordinated
with the line of the image formed on the monitor 22. This is
accomplished through the use of common synchronism sources 24
and 26, one for vertical control of the raster scan and one fox
the horizontal control. In this manner the intensity variations
over the surface of the specimen which are caused by one or
more of the changing parameters such as topography, composition,
and electrostatic charge may be imaged on the surface to the
monitor, in synchronization with the advance of the scanning
microprobe.
Photomicrographs are produced with the aid of a
photographic system 28 to capture and permanently retain the image
of the monitor, usually on the inclusion of an additional
monitor, of the general type of monitor 22. As is common in
television systems, video blanking pulses are generated in
video blanking control 30 to blank out the electron beam of the
monitor during the video retrace of the raster scan. Particular
mention of video blanking is made at this juncture, since
special use of video blanking is employed in the production of
multiple images on monitor 22 in accordance with the invention.
One embodiment of the present invention will be described
which exhibits real time stereoptic viewing of a selected area of a
specimen. Other embodiments which illustrate simultaneous
comparative viewing of different responsive returns will be
additionally described with reference to the stereo electron
microscope. In the present embodiment of the invention, left and
right views 12 1 and 12 r of the sample are imaged on left and right
halves of the monitor 22 (See Figure 2). The stereo viewer 32
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superimposes the two individual images for the e~es of the
observer to resolve. To create these left and right views of
the sample, the electron beam is caused to strike a preselected
area on the sample by causing the beam to sequentially scan the
selected area of the sample at two preselected, opposite scan
angles. The amplitude of this scan angle, or more particularly,
stereo incidence angle, influences the observable stereopsis,
and is thus desirably controllable by the operator of the
electron microscope. Accordingly, an operator control 34 is
placed on the control panel of the instrument.
Stereo Mode reference control 36 is a reference
signal generator which provides a signal to alternate the stereo
incidence angle from the right viewing angle to the left viewing
angle at a predetermined rate.
Referring now to Figure 2a and 2b, the stereo viewer
32 which provides simultaneous viewing of the separate left and
right images and the generation in the viewer's mind of the
stereoptic image. As will be subsequently explained, Figure 2
illustrates the side-by-side left and right images are generated
on the tube face 22a of the monitor 22 of Figure 1. The viewer
optics at a distance Zr (Figure 2b) superimposes the two images
at an apparent distance Za The convergence angle ~ is
achieved by the combined effects of a pair of prisms and a pair
of lenses, while the focus of the observers eyes on each image
is removed to the same distance Za by means of the lens pair
only. This matching convergence and focus results in the most
comfortable stereo viewing.
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The creation of the split screen, simultaneous side-
by-side images is illustrated in Figures 3 and 4a through 4c.
Novel generation of the side-by-side images is obtained through
the continuous scanning of the sample surface and the entire
face of the monitor, with appropriate use of coordinated video
blanking on the monitor face and shifting of the stereo incidence
angle. In the incidence of comparative viewing of the different
responsive return (eg, backscattered vs. secondary electron
return) the blanking is coordinated with shift of detector
function. The present detailed dPscription will be devoted to
the production of the stereo images, and comparative viewing
will be discussed later.
- For one field, which in the described embodiment is
1/60th of a second, the television video is blanked on the last
one half of each horizontal scan line. This, then, causes the
right hand one half of the monitor screen to be dark. Correspond-
ingly, the left side of the screen generates an image according
to whatever signal is input to the monitor beam brightness
;; control. In this stereo example, the microprobe beam is scanning
the sample at the incidence angle ~ 1, as is illustrated on
Figure 3a. Upon completion of the first field, the video
blanking is applied to the left, or first one half of each
horizontal scan line and the second half or the right hand portion
is imaged on the face of the monitor, providing an image according
to the detected response of the microprobe beam striking the
surface of the sample at the opposite stereo incidence angle ~ r.
It may be realized that a change in magnification of
the microscope could cause a misalignment of the left and right
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images on the monitor. This i8 illustrated in Figure 3b wherein
lateral displacemen~ of the previously aligned images may be
seen. Change in amplitude of horizontal sweep amplitude re-
sulting from change of magnification of the microscope causes
the image to be shifted to the left. If this horizontal sweep
is held in phase with the television horizontal sweep and no
magnification dependent offset is injected, the left and
right unblanked centers don't remain coincident. In order to
ensure that the areas Ar and Al on the sample remain coincident
lQ with the other, with changes in area size, as caused by change
in magnification, a phase shift is introduced between the
television horizontal sweep and the microprobe horizontal
sweep. This is illustrated in Figure 4~ Figure 4a shows that
the horizontal synchronization and sweep of the television
are caused to remain unchanged at all times. However, while
the right half of the television video is blanked, the synchroni-
zation and horizontal sweep of the microprobe beam striking the
sample are changed in phase with respect to those of the tele-
vision (Figure 4b!. The horizontal ramp of the beam coincides
timewise with the center of the left half of the television. In
this way a change in magnification (or horizontal ramp amplitude)
does not shift, causing a lateral shift of the image. During
the succeeding field, or l/60th of a second, while the left half
of the television is blanking, and the beam horizontal synchroni-
zation and ramp are shifted in phase to the center ramp or the
middle of the right half of the television screen. Once again,
it may be observed that with the above procedure, the change in
magnification of the microscope causes no change or lateral
motion of the image.
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In the illust~ated embodiment the rate at which the
beam i5 switched between left and right incident angles is 60 Hz.
For geographic areas with electrical power systems of different
frequency, the preferred instrument would be of similar frequency
to take advantage of the synchronization. The synchronization
signal for this switching is obtained from the normal vertical
synchronization source, for the scanning electron microscope,
which is 24 on Figure 1 and 24 on Figure 5. A square wave of
30 Hz rate is generated as a stereo reference by flip flop 42.
As illustrated, when the stereo control (flip flop 42) is
selected to either the right or left position, a constant d-c
signal is output, the polarity being reversed, one with respect
to the other. This output signal thus becomes the master
instruction to the instrument as to stereo function. According
to the instruction of the stereo control, the blanking control
will perform the proper synchronized blanking of the monitor,
based upon whether the flip flop indicates the generation of
the right hand or left hand image at the sample.
The stereo reference source 42 input a signal to the
video blanking control 30 so that a square wave output may be
generated for blanking instruction. This signal includes the
variable pulse length information necessary to cause proper
centering of the division line between the left and right
images. Thiæ signal is illustrated at Figure Sa as including
the horizontal retrace of the television horizontal synchroniza-
- tion, a 63 microsecond signal. The blanking signal generator
output reflects the lack of a blanking signal in those instances
where the system is operated in left or right mode and the flip
flop stereo reference outputs a steady plus or minus d-c signal.
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The stereo control of the microprobe beam (14 of Figure
1) includes (on Figure 5) a horizontal sync delay 44 to accommodate
for the previously discussed change of magnification. The
phase of the delayed synchronization with respect to the television
synchronization is determined by the square wave input from the
stereo reference 42. To accomplish the double deflection of
the microprobe beam, the stereo reference output i8 supplied
to a variable voltage divider 46~ The voltage signal picked
off of divider 46 is supplied to a current generator 48 which,
in turn, is supplied to the lower set of horizontal deflection
coils 50 within the microscope column. This 30 Hz flip flop
stereo reference signal is superimposed on the 15 Hz horizontal
sweep signal being output by the deflection amplifier 52.
These signals are shown as electrically superimposed on a
single coil. It ~hould be recognized that the superimposition
may be accomplished magnetically, by separate coils, disposed
adjacently. In order to counteract this sidestep of the beam,
or to bring it back onto the sample, at the desired incidence
angle, the same flip flop reference signal is current referenced,
in amplifier 54 and supplied to the upper horizontal deflection
coils 56. Recognizing that adjustment of these deflection
signals with respect to each other may be necessary, a voltage
divider 58 is provided. This provision enables location of the
convergence point of the microprobe beam for the left and right
paths. Once this convergence point has been established, i.e.,
positioned on a point of interest on the sample, the stereo
effect may be altered by varying control 46, in effect, varying
the gain of the stereo amplifier.
Vertical alignment of the left and right images is
accomplished by supplying the stereo reference square wave to
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the upper vertical deflection coils 60 via a current source 62.
A voltage divider 64 on the input side of the current amplifier
62 allows for adjusbment of the input of the signal to the
upper vertical deflection coils.
In order to optimally focus the left and right images
a small electromagnetic lens 70 is provided in the column of the
instrument. The current to the coil of lens 70 is adjustable
through separate voltage dividers 72 and 74 in an amplifier 76
which provides the input to the coils 70. The divider 72 is
operatively connected to function in conjunction with the stereo
reference signal at the left image position and divider 74
operatively connected to function in conjunction with the stereo
reference signal at the right image position.
Similarly, independent stigmation of the left and right
images is effected by feeding two separate control inputs 82 and
84 into a gate circuit 86 which is fed by the stereo reference
; signal. According to which of the image positions is being
interrogated, the selected astigmatism correction forleft and
right image is supplied to the stigmator coils 80 in the electron
microscope column.
As a matter of convenience, a reversal switch 90 is
included in the stereo reference signal circuit. Upon reversal
of the position of the switch 90, the phase of the stereo
reference signal going to all beam deflection and focus circuitry
is changed. This results in the left view of the specimen being
presented on the right side of the television monitor and the
right view on the left side of the television monitor. This
reversal is useful to instrument operators who wish to observe
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the stereopsis by eye accommodation (crossed eyes) and without
the aid of stereo viewer 32 (Figure 1). For those applications
where it is desirable to compare different classes of emission
response fxom the sample 12, an additional detector 18' may be
included within the electron microscope. The output of this
detector, as with detector 18, is supplied to the video amplifier
20'. The stereo reference circuit 42 now operating strictly
as a flip-flop, may gate the response of these detectors
to sequentially appear as the left and right images
of monitor 22. Similarly, with the stereoscopic e~bodiment
an entire field will be imaged on one side of the monitor such
as to output from detector 18 giving perhaps back-scattered
electron information. The successive field placed on the right
side of the monitor may be that provided by detector 18'
which could be secondary electron response from the sample 12.
The function of the stereo control circuit in this case would
be to alternately provide monitor 22 with the information from
detector 18 or 18' according to the flip-flop circuit's
instructions to the monitor and the blanking circuits as to
which of the left or right images is being generated.
It will be recognized by those skilled in the art
that numerous other variations of the illustrative apparatus
may be accomplished. It, however, should also be appreciated
that these may properly be considered as falling within the
scope and spirit of the present invention.
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