Note: Descriptions are shown in the official language in which they were submitted.
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X-Y ~DDRESSABLE WORKPIECE POSITIONER
HAVING AN IMPROVED X-Y ADDRESS
_ INDICIA SENSOR
BACKGROUND OF THE INVENTION
The present invention relates in general to X-Y
addressable workpiece positioners and, more particularly,
to an improved positioner particularly useful in an
alignment and exposure machine of the type employed for
sequentially aligning images of different regions of a
semiconductive wafer with a mask and for exposing each
such region of the semiconductive wafer in accordance
with a pattern of the mask.
DESCRIPTION OF THE PRIOR ART
Heretofore, X-Y addressable workpiece positioners
have been proposed in which a mask is sequentially stepped
to different X and Y, coordinates for sequentially exposing
different por-tions of the mask in accordance with a
pattern of a reticle. One such prior art stepper is
manufactured by Jade Manufacturing Co. In that stepper
the mask is disposed on a work stage tha-t is addressably
movable to different X and Y coordinates along coordinate
X and Y axes and that is sequentially addressed to position
different regions of the mask for exposure in accordance
with the pattern of the reticle. Two separate one-
dimensional arrays of respec-tive X and Y parallel scribe
lines are affixed to the work stage for use in moving it
to the X and Y coordinates of an addressed position
selected by an operator. Sensors are set up to sense the X
and Y coordinates of an addressed position of the work stage by
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respectively se~uentially sensing the X and Y scribe lines o*
these arrays. X and Y servo motors responsive to the sensed X
and Y coordinates move the work stage to the addressed position
selected ~y the operator. However, the work stage does not move
simultaneously along both the X and Y axes to the addres~ed posi-
tion. Rather, the Y co~rdinate of the addressed p~sition is first
sensed and the work stage moved along the Y axis to that Y coor-
dinate. Then the X coordinate of the addressed position is sensed
and the work stage moved along the X axis to that X coordinate.
This stepper has the disadvantage that the work stage cannot
move along the shortest path from a first addressed position to
a second addressed position, but, on the contrary, must move from
the first addressed position ~o a reference position from which
the X or the Y scribe lines may be sequentially sensed for moving
the work stage to any new X or Y coordinate, respectively, of the
second addressed position. If the seeond addressed position has
both new X and Y coordinates, the work stage is initially
moved to a reference position from which the Y seribe lines are
sequentially se~sed and the work stage moved to another reference
position having the new Y eoordinate. From the latter reference
position the X scribe lines are sequentially sensed and the work
stage move~ to the second addressed position having both the new
X and Y c~orainates. In addition, this stepper depends for its
accuracy upon the orthogonality of Y axis beaxing support of the
work stage with resp~ct~to the X axis of motion of the work stage.
While this orthogonality can be accurately controlled, i~ re~uires
exp~nsive c~mponents to do so.
It is also known, from the prior art in sueh addressable
workpiece positioners, to employ a mirror affixed t~ the work
stage for movement therewith and thus for movement with the workpieee.
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A laser beam is directed along an optical path onto
the mirror in such a manner as to produce X and Y
interference fringes of the laser beam, such fringes
being counted for precisely positioning the work
5 tage and, hence, the workpiece at the X and Y
coordinates of an addressed positlon.
The problem with thls scheme is that the
standard for determining both the X and Y coordinates
of an addressed position of the workpiece is the
wavelength of the laser beam. The wavelength of the
laser beam, however, is a function of the temperature,
pressure and humidity of the optical path used to
produce the interference fringes. As a consequence,
the work stage must be contained within an environmental
chamber for controlling the temperature, pressure and
humidi.ty to a very high degree. Such a chamber is
relatively expensive and complicates the addressable
workpiece positioner and the use thereof.
Therefore, a less expensive and less compli-
cated X-Y addressable workpiece positioner is desired
which is capable of moving a work stage for a workpiece
to a sequence of repeatably addressed positions with
an accuracy of better than one tenth of a micron. It
is also desired that the work stage move in a more
direct path from a first addressed position to a
subsequent addressed position so as to reduce the
time required for moving between the sequentially
addressed positions.
SUMMARY OF THE PRESENT INVENTION
Various aspects of the invention are as follows:
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An X-Y addressable workpiece positioning
method comprising the steps of:
coupling a workpiece to a work stage movable in
X and Y directions within a common plane of movement
defined by the X and Y directions and wi~hin which the
workpiece is to be positioned, the work stage having a
two-dimensional array of X and Y coordinate positioning
indicia affixed thereto for effecting positioning of
the work stage with the workpiece;
projecting an enlarged image of at least a portion
of the array of X and Y coordinate positioning indicia
onto a relatively stationary sensor stage;
sensing the enlarged image through at least two
pairs of pattern recognition windows for independently
recognizing and sensing the X and Y coordinate positioning
indicia of the enlarged image to determine the X and Y
coordinates of the position of the work stage, a sensed
output being derived through each window of each pair of
pattern recognition windows;
subtracting the sensed output derived through one
window of each pair of pattern recognition windows from
the sensed output derived through the other window of
the same pair to cancel ambient background effects;
comparing the X and Y coordinates of the position
of the work stage with the X and Y coordinates of a
different position of the work stage to derive an error
output; and
moving the work stage with the workpiece and the
array of X and Y coordinate positioning indicia to the
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different position in response to the error output.
An X-Y addressable workpiece positioning method
comprising the steps of:
coupling a workpiece to a work stage movable in X
and Y dlrections within a common plane of movement defined
by the X and Y directions and within whîch the workpiece
is to be positioned, the work stage having a two-dimensional
array of X and Y coordinate positioning indicia affixPd
thereto for effecting positioning of the work stage with
the workpiece and provided with X and Y border indicia for
referencing the X and Y coordina~e positioning indicia,
respect.i~ely;
projecting an nlarged image of at least a portion of
the array of X and ~ coordinate positioning indicia onto
a relat.ively stationary sensor stage for sensing the X
and Y coordinate positioning indicia of the enlarged
image to derive an outpu~ determinative of the X and Y
coordinates of the position of the work stage;
mo~ing the work stage so that the sensor stage is
operable for sequentially sensing the X and Y border
indicia of the enlarged image, and referencing the sensed
X and Y coordinate positioning indicia to the sensed X
and Y border indicia, respectively;
comparing the X and Y coordinates of the position
of the work stage with the X and Y coordinates of a
different position of the ~ork stage to derive an error
output; and
moving the work stage with the workpiece and the
array of X and Y coo.rdinate positioning indicia to the
different position in response to the error output.
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An X Y addressable workpiece positioning method
comprising the steps of:
coupling the workpiece to a work stage movable in
X and Y directions wi~hin a common plane of movement
defined by the X a~d Y directions and within ~hich the
workpiece is to be positioned, the work stage having a
two-dimensional array of X and Y coordinate positioning
indicia affixed thereto for effecting positioning of
the work stage with the workpiece and provided with X
and Y border indicia for referencing the X and Y
coordinate positioning indîcia, respectively;
projecting an enlarged image o, at least a portion
of the array o X and Y coordinate positioning indicia
onto a relatively sta~ionary sensor stage;
sensing the enlarged image through at least two
pairs of pattern recognition windows for independently
recognizing and sensing the X and Y coordinate positioning
indicia of the enlarged image to determine the X and Y
coordinates of the position of the work stage, a sensed
output being derived through each window of each pair
of pattern recognition windows;
subtracting the sensed output derived through one
window of each pair of pattern recognition windows from
the sensed output derived through the other window of
the same pair to cancel ambient background ef~ec~s;
mo~ing the work stage with the workpiece so that the
sensor stage is operable for sequentially sensing the
X and Y border indicia of the enlarged image through
respecti~e X and Y border sensing windows, and referencing
the sensed X ~nd Y coordinate positioning indicia to the
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sensed X and Y border indicia, respectively, the X and Y
border sensing windows being located in the sensor s~age
closer to the respec~ive X and Y border indicia of the
enlarged image than the center of each respective pair of
pattern recognition windows so as to permit the pairs of
pattern reco~lition windows to be employed for sensing~the
X and ~ coordinate positioning indicia of the enlarged
image while the X and Y border sensing windows are employed
for sensing the respective X and Y border indicia of
the enlarged image.
An X-Y addressable workpiece positioning
apparatus comprising: .
work stage means movable in both X and Y directions
within a common plane of mo~ement defined by the X and
Y directions and within which a workpiece is to be
positioned;
the work.stage means including holding means for
holding the workpiece for movement with the work stage
means;
indicia means comprising a two-dimensional array of
X and Y coordina~e positioning indicia affixed to the
work stage means and movable therewith for effecting
positioning of the work stage means;
relatively stationary sensor stage means for
determining the X and Y coordinates of the work stage
means;
projector means for projecting an enlarged image of
at least a portion of the array of X and Y coordinate
positioning indicia onto the sensor stage means;
.
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the sensor stage means including at least two pairs
of pattern recognition wind~ws and corresponding sensing
means for independently recognizing and sensing the X
and Y coordinate positioning indicia of ~he enlarged image
to derive a sensed output through each window of each
pair of pattern recognition windows and determine the X and
Y coordinates of the position of the work stage means,
the sensing means being coupled for subtracting the
sensed output derived through one window of each pair of
pattern recognition windows from the sensed output
derived through the other window of the same pair to cancel
ambient background effects;
comparative means for comparing the X and Y coordinates
of the position of the wsrk stage means with the X and Y
coordinates of a different position of the work stage means
to derive an error output; and
drive means for moving the work stage means and
the array of X and Y coordinate positioning indicia to
the different position in response to the error output.
An X-Y addressable workpiece positioning
appara~us comprising:
work stage means movable in both X and Y directions
within a common plane of movement defined by the X and
Y directions and within which a workpiece is to be
positioned;
said work stage means including holding means for
holding the workpiece for movement with the work stage
means;
indicia means comprising a two-dimensional array of
X and Y coordinate positioning indicia affixed to the
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work stage means and movable therewith for effecting
posi~ioning of the work stage ~eans, and X and Y border
indicia for referencing the X and Y coordinate positioning
indicia, respectively;
relatively s~ationary sensor stage means for deter-
mining the X and Y coordinates of the work stage means;
p~ojector means for projecting an enlarged image of
at least a por~ion of the array of X and Y coordinate
positioning indicia onto the sensor stage means so that
the X and Y coordinate positioning indicia of the enlarged
image may be sensed by the sensor stage means;
dr~e means for moving the work stage means so that the
X and ~ border indieia of the enlarged image may b~
sequentially sensed by ~he sensor stage means and the sensed
X and Y coordinate positioning indicia referenced to the
sensed X and Y border indicia, respectively, to d~termine
the X and Y coordin~tes of the position of the work stage
means; and
comparative means for c~mparing the X and Y coor~
dinates o~ the position of the work stage means with
the X and Y coordinates of a different position to derive
an error output, the drive means being operable for moving
the work stage means and the array of X and Y coordinate
positioning indicia to the different position in response
to the error output.
An X-~ addressable workpiece positioning
~pparatus comprising:
work stage means movable in both X and Y directions
within a common plane of movement defined by the X and
Y directions and within which a workpiece is to be
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positioned;
~ he work stage means including holding means for
holding the workpi~e for movement with the work stage
means;
indlcia means cvmprising a two-dimensional array of
X and Y coordinate positioning indicia affixed to the
work stage means and movable therewith for effecting
indicia for referencing the X and Y coordinate position-
ing indicia, respectively;
relatively stationary sensor stage means for deter-
mining the X and Y coordinates of the work stage means;
projector means for projecting an enlargPd image
of at least a portion of the array of X and Y coordinate
positioning indicia onto the sensor stage means;
the sensor stage means including at least two pairs
of pattern recognition windows and corresponding sensing
means for ind~pendently recognizing and sensing the X and
Y coordinate positioning indicia of the enlarged image
to derive a sensed output through each window of each pair
of pattern recognition windows and determine the X and Y
coordinates of the position of the work stage means, means
for subtracting the sensed output derived ~hrough one
window of each pair of pattern recognition windows from
the senséd output derived through the other window of the
same pair to cancel ambient background effects, and a pair
of X and ~ border recognition windows and corresponding
sensing means for sensing the respective X and Y border
indicia of the enlarged image, the X and Y border
recognition windows being disposed closer to the respective
X and Y border indic;ia of the enlarged image than the
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respective pairs of pattern recognition windows so as to
permit sensing of the X and Y coordinate positioning indicia
of the enlarged image while simultaneously sensing the X
and Y border indicia of ~he enlar~ed image; and
comparative means for comparing the X and Y coordinates
of the posltion of t~e work stage means with the X and
Y coordinates of a different position to derive an error
output, the drive means being operable for moving the
work stage means and the array of X and Y coordinate
positioning indicia to the different position in response
to the error output.
An address~ble workpiece positioner comprising:
stage means for holding a workpiece, the stage means
being movable along a pair of coordinate axes to addressable
coordinatP positions in a plane containing those axes and
having-a t~o-dime~io~al ~rray of c~ordina~e addressing
indicia affi~ed thereto for Yement therewith;
~ ensor means for d~termining the addressable coordinate
position of the stage means;
optical means for projecting an lmage of a portion of
the array o~ c~Drdinate addres6ing indicia onto the sensor
m~ans;
the ~ensor means including at least tw~ pairs of ~ensing
m~ans for ~ensin~ the coordinate addressing indicia of the
~mage to determine the addressable coordinate position of the
stage means;
compensa'cing means, iracluding each pair of sensing means,
for compensating ~or ~esired variations in the intensity of
th image;
control ~neans for comparin~ the ~ddressable coordinate
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257
position of ~che s~age means with another addressable coordina~e
po6i~ion tv deri~e an error signal; and
drive means for ~oYing ~ch~ ~age means and che array of
coordina~ addre~sing indicia ~o ~aid oth~r addressable
coordinate position in response to the error signal.
An addressable workpiece positioner co~.prising:
~ age means for holding a workpiece, ~che ~age means
~eing vable along a pair of cc>ordinate axes ~o addr~ssable
c~ordi~ate positions in a plane containing those axes;
f~en~t~r Dleans for determinin8 the addressable coordinate
p~sitio~ of the ~ cage ~eans;
~ he ~tage ~e~ns ~ncluding indicia means affi~ed ~hereto
for movemer~t therewi~h ~o effec~ cQordinate positionirlg of
the stage means, the indicia ~ans including coordinate reference
indicia and a two~di~nsional arra~ ~ coordinate addressing
indicia;
opticsl means for ~r~ecting an ~ ge of ~ portion of
the indicia ~ea~ ~nto the ~ens~r ~an~;
the ~ensor means lncluding first æe~sing me~n~ for
8en8~ng the coordina~e re~erence indicia of the im~ge, and
second ~ensing means for 6ensing the cooxdinate addressing
indicia of the ~mage with reference to ~he sensed eoordinate
reference indicia to de~ermine the addressable coordinate
position of the ~tage means;
control means for comparing ~he addressable coordina~e
position of the stage means with another addressable coordinate
posi~ion to der Ye an error signal; and
drive means or moving the ~tage means and the indicia
means to ~aid other addressable coordinate position in response
to the error 8 ignal
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An addr~;~s~ble workpiece positioner comprising:
st~ge means, movable along a pair of coordinate axes,
for holding a workpiece to be positioned;
a ~wo-dimensional array of coordinate addressing indicia
~oge~her with coordina~e referen indicia for the array of
eoordinate addressing indicia, affixed to thP stage means,
or moveme~t wit~ the ~tag means;
sensor ~eans for ~ensing the coordinate addr~ssing
indicia and khe coordina~e reference i~dicia to provide
output lnformation determina~ive of the coordin~te posi~ion
of the ~tage means; and
. control mean~, responsive to output information from
the sensor means and to input control inforcation, for moving
~he sea~e ~an~ to coordinate positions dete~mined by the input
control inform~tion.
hn addressable workpiece positi-oner comprising:
~ tage means, m~able along a pair of coordina~e a~e ,
for holding a workpiece to be po~itioned;
a ~wo-dimensional array of coordinate address~ng indicia,
affi~ed to the ~tage m~ans, for movement with the stage means;
said coordinate addressin~ indicia being uniformly
arrayed in rows paral~el ~o one of the c~o~diDate axes and in
columns parsllel to the other of t~e coordinate a~es;
8en80r means for sensing the roordinate addressin~
~dlcia to pr~ide output information determinati~e of the
coordinate posi~ion of the etage means;
~ aid sensing means i~cluding at least a first pair of
~en~ing means disposed for ~ensing the coordinate addressing
indicia arrayed in rows parallel to ~aid one of the c~ordinate
a~es to provide output information determinative of one
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c~ordinate of the coordinate position of the stage means, and
a~ least a second pair of sensing means disposed for sensing
the coordinate addressing indicia arrayed in columns parallel
to ~aid other of ~he coordinate axes to provide output informa-
~ion determina~ive of another coordinate of the coordinate
position of ~he stage means;
optical means for proj ecting an im~ge of a portion of
the array of coordinate addressing indicia onto the ~PnSor
me ns;
compensating me~ns, includi~g eaeh pair of ~ensin~ means,
for co2pensating for undesired variations in the lntensity
of the image; and
eon rol ~eans, responsive ~o ~he output informa~ion from
the ~en~or mean~ ~d to input control information, for mo~ing
the ~tage means to ~oordin~te positions determined by the
~nput control information.
An addressable workpiece positioning method
comprising t~e ~eps of:
placine the work~iece ~o be positioned on a stage that
is movable along coordinate axes in a plane con~aining or
parallel ~co those axes and that has a ~wo-dimensional array
of coordinate atdressing indicia affixed thereto for movement
therewith;
projecting an image of a~ least a portion of ~he array
of coordinate addressing indicia onto a sensor;
sensing the coordinate addressing indicia through a~
least ~wo pairs of pattern recognition windows included in the
~ensor with each pair disposed for independently recognizing
and sensing coordinate addressing indicia aligned parallel to
a differen~ sne of ~he coordinate axes to derive output
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~nform~ti~n determlnative of a different coordinate of the
p~sition of the s~age ~nd to derive a ~ensed ~utpu~ through
each window of each pair;
~ ubtr cting the s~nsed output deri~ed ~hrough one window
of each pair of pat~ern recogni~ion windows from ~he sen~d
~ut~ut deriv~d ~hrough the other window of the ~Eme pa~r to
c~mpensate for undesired ~ariati~ns in the intensity of ~he
~mage;
com~aring the coordinate po~it~on of ~he ~tage with a
de~ignat~d coordina~e position to derive an error outpu~, and
moYing ~he ~tage ~o the designated coordinate po~ition
in re~p~nse ~ ~he ~rr~r ou~put.
An adaptive servo control system comprising:
first and second stage means respectively movable
along orthogonal axes for positioning a work~iece relative
to a work apparatus;
first and second drive means res~ectively responsive to
first and second drive signals and operative to drive said
first and second stage means along said axes;
position detector means for monitoring the position
of said first and second stage means rela~ive to the work
a~para~us and including
a reference substrate carried by one of said
stage means and having orthogonal dimension Position
related indicia disposed thereupon,
said indicia including a plurality of like,
rectangularly-shaped reflective surface areas arrayed
in orderly r~ws and columns,
said reference substrate including a reference
strip c~mprising a re~lective band circumscribing said
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re1ect.ive areas, and
means for sensing said indicia and developing
first and second ac.tual position signals correspondin~-
to the positioning of said substrate along said axes;
input means for generating first and second desired
position signals corresponding to positions along said axes
~o which said first and second stage means are to be driven;
and
f~rst and second position control means for respec-
ti~ely comparing said first and second desired position
signals to said first ~nd second actual position signals and
for developing said first and second drive signals for appli-
cation to said first and second drive means,respectively, to
cause said workpiece to be driven to a desired position.
An adaptive servo control system comprising:
first and second stage means respectively movable
along orthogonal axes for positioning a workpiece relative
to a work apparatus;
first and second drive means respec~ively respon-
sive to first and second dri-ve signals and operative to drive
said ~irst and .second stage ~eans along said axes;
position detector means for monitoring the position
o~ said irst and second stage means relative to the work
appara us ~nd inc.luding
~ re~rence substr~te carried by one o~ said
stage means and having orthogon~l dimensi.on posi-
tion related indicia disposed thereupon,
said indicia including a pl~rality of like,
rectangularly~sh~ped ~paaue sur~ace areas arrayed in
orderly rows and columns,
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s~id reference s,ubstrate including a reference
strip comprising an opaque band circumscribing said
opaque surface areas, and
means ~or sensing said indicia and developing
first ~nd second actual position signals corresponding
to the positioning of said su~stra~e along said axes;
input means for generating first and second desired
position signals corresponding to positions along said axes
to which said first and second stage means are to be driven;
and
first and second position control means for respec-
tively comparing said first and second desired position
signals to said firs~ and second actual position signals and
for developing said first and second drive signals for appli-
cation to said first and second drive means,respectivelv, to
cause said workpiece to be driven to a desired position,
A servo 'control system comprising:
stage means movable along orthogonal axes for positioning
a workpiece relative to a work apparatus;
~irst and second drive means respectively responsive
to first and second drive signals and operative to drive said
stage means along said axes;
position detector ~eans for monitoring the posi~ion
of said stage means relative to the work apparatus and
including
a refPrence substrate carried by said stage
means and h~ving orthogonal dimenslon position
related indicia disposed ~hereupon,
said indicia incl~ding a plurality of like,
rectangularly-sha~ed reflective surface areas arrayed
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3L2~L7~S~
in orderly rows and columns,
s~id re~erence subs~rate including a reference
strip comprising a reflective band circumscribing said
reflec~i~e areas, and
means for sensing said indicia and de-veloping
first and second actual position signals corresponding
to the positioning of said substrate along said axes;
input means for generating first and second desired
position signals corresponding to positions along said axes
to which said stage ~eans is to be driven; and
first and second ~osition control means for respectively
comparing said irst and second desired position signals to
said first and second actual position signals and for developing
sai.d first and second drive si~nals for application to said
first and second drive means,respectively,to cause said work-
piece to be driven to a desired position.
A servo control system comprising:
stage means movable along orthogonal axes for positioning
a workpiece relative to a work appara~us;
first and second dri~e means respectively responsive
to first and second drive signals and operative to drive said
stage means along said axes;
position detector means for monitoring the position
of said stage means relati~e to the work apparatus and
including
a reference substrate carried by said stage means
and having orthogonal dimension position related indicia
disposed thereupon,
said indicia inciuding a plurality of like,
rectangularly-shapPd opaque surface areas arrayed in
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~ 2
orderly rows and c'olumns,
said reference substrate including a reference
strip comprising an opaque band circumscribing said
opaque surface areas, and
means ~or sensing said indicia and developing
first and second actual position signals corresponding
to the positioning of said substrate along said axes;
input means for generating first and second desired
position signals corresponding ~o positions along said axes
to which said stage means is to be driven; and
first and second position control means for respectively
comparing said first and second desired position signals to
said first and second actual position signals and for developing
said first and second drive signals for application to said
first and second drive means,respectively,to cause said work~
piece to be driven ~o a desired position.
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BRIEF DESCRIPTION OF' THE DRAWINGS
Figure 1 is a perspective view of a step-and-
repeat alignment and exposure machine employing
features of the present invention.
Figure 2 is a sche~atic perspective view,
partly in block diagram form, of a portion (including
an X-Y addressable workpiece positioner employing
features of the present invention) of the machine of
Figure 1.
Figure 3 is an enlarged detailed view of a
portion of an array of X and Y coordinate addressing
indicia employed as part of a work stage of the positloner
of Figure 2 as delineated by line 3-3.
Figure 4 is a plot of -triangular output current
waveforms derived
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1217~257
from an X coordinate addressing indicia sensing portion of a
sensing diode plate employed in the positioner o~ Figure 2 as a
function of movement of the work stage in the X direction.
Figure 5 is a plot of square wave output wa~eforms derived
from the ~riangular output current waveforms of Figure 4.
Figure 6 is a plot of a portion of one trian~ul-~r output
current waveform of Figure 4 employed in locking the work stage
to the X coordinate of an addressed position.
Figure 7 is a plot of signal intensity of another output
waveform derived from a border sensing portion of the sensing
diode plate of Figure 2 as a function of distance away from a
border enclosing the array of X and Y coordinate addressing indicia.
Figure 8 is a schematic circuit diagram of a border sensing
circuit employed for sensing the border enclosing the array of
X and Y coordinate addressing indicia.
DESCRIPTION OF THE P~EFERRED _ MBODIMENTS
Referring now to Figure 1, there is shown a step-and-repeat
projection alignment and exposure machine 20 incorporating features
of the present invention. This machine 20 includes a base unit
22, a precision work stage 24 supported on the base unit for holding
a workpiece, such as a semiconductive wafer 30, and for precisely
positioning the workpiece along coordinate X and Y axes in a hori-
zontal plane. An optical unit 26 is supported from the base unit
22 for use in aligning and exposing the wafer 30. An automatic
workpiece handling unit 28 is also supported on the base unit 22
for transporting wafers 30 to and from the work stage 24. The
base unit 22 includes a stationary granite block having an upper
reference surface which is flat to within one micron across the
surface thereof and havin~ a cylindrical bore extending vertically
therethrough for a sensor stage 46 ~see Figure 2).
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Referring now to both Figures 1 and 2, in operating the align-
ment and expo~ure machi~e 20, the operator introduces a wafer 30
into the automatic workpiece handling unit 28 which then precisely
positions the wafer on the work stage 24. The operator moves a
microscope 105 of the optical unit ~6 into position for use with
a projection lens 10~ in viewing a pattern bearing surface of a
photographic mask 98 and an image of an addressed region of the
upper surface of the wafer 30 to be precisely opti~ally aligned.
Following this alig~ment, the addressed region of the upper sur-
face of the wafer 30 is exposed in accordance with the pattern ofthe mask 980
The operator selects the address2d region of the wafer 30 to
be exposed in accordance with the pat~ern of the mask 98. X and Y
~ervo motors 76 and 77 are coupled to the work stage 24 for moving the
work stage and a two-dimenslonal array 45 of X and Y coordinate address-
ing or positioning indicia affixed thereto over the sensor stage 46
to position the addressed region of the wafer 30 for exposure. The
operator then views the addressed region of the wafer 30 ill~minated
by light pro~ected through the optical unit 26 onto the addressed
region of the wafer. An image of the illuminated addressed reglon
o~ the wafer 30 is projected onto the back side of the mask 98 a~d
thereby superimposed on the pattern of the mask for viewing by the
operator through the microscope 105 while controls are manipulated to
adjust the position of the sensor stage 46. ~his manipulation causes
a slight correction to b~ made in the position of the work stage 24
(~hen locked to ~ove with the sensor stage 46) for precisely aligning
the viewed image of the illuminatPd addressed region of the wafer 30
with the pattPrn of the mask 98~ The operator ~hen moves the micro-
~cope 105 out of the way and moves a projection light source 29 into
position for exposing th0 address~d region of the wafer 30 in accor-
dance with the pattern of the ma~k 9B through the projection
lens 104. Follc~wing this expo ure, t:he progra~uner 73
-11-
~ ~ ~ 7 ~ ~ ~
causes the work stage 24 to advance ~o the next addressed
position at which another region o~ the wafer 30 is exposed. The
wafer is sequentially exposed by this step-and repeat process until
the wafer is totally exposed, at which point the operator or
progra~ner initiates operation of the automa~ic workpiece handlin~
unit 28 to r~move the exposed wafer from the work stage 24 and
advance a new wafer into position on the work stage.
Referring now specifically to Figure 2, there is shown an X-Y
addressable workpiece positioner forming part of the alignm~nt
and exposure machine 20 of Figure 1 and incorporating features of
the present invention. In this workpiece positioner, the wafer 30
is positioned on and held by the work stage 24 above the array 45
of X and Y coordinate addressing indicia affixed to and moveable
with the work stage. The sensor stage 46 is disposed below the
work stage 24 and the array 45 of addressing indicia. A lamp 47
provides illumination that is projected by a lens 48 into a beam
directed onto a beam splitting mirror 49, which in turn directs
the illumination through a magnifying lens 51 on~o a relatively
small region of the array 45 of X and Y coordinate addressing
indicia for illuminating same.
~ n image of the illuminated region of the array 45 of X and Y
coordinate addressing indicia is projected via the magnifying lens
51 through the beam splitting mirror 49 and focused onto an opaque
sensing window plate 5~ forming part of the sensor stage 46 and
having a plurality of different windows 53 fonned therein and
disposed along the coordinate X and Y axes for sensing th~ X and Y
coordinate addressing indi.cia. In a typical example, the
magnification M of the magnifying lens 51 is 13X such that th~
aforementioned image, as projected onto the sensing window plate
52, is thirteen times actual size The windows 53 permit
the light incident thereon to pass therethrough to respective
X -12-
7~2~7
stick lenses 54 arranged in registration with the respective
windows. Thus, the stick l~nses 54 receive the light p2ssing
through the r~spective windows 5 3 ~nd focus tha~ light onto res-
pective PIN diode~ 55 disposed on a ~ensing diode plate 56 of the
- ~ensor s~age 46.
~ wo pairs 57 of the diodes 55 are arranged and connected for
recognizing and sensing the X coordinates of the array 45 of
addressing indicia, whereas two additional pairs 5B of the dio~es
55 a~e arranged and connected for s~nsing the Y co~rdinates of
the array 4~ of addressing indicia. qhe diodes of each pair 57
and 5B are connected in bucking relation so as to provide a zero
output when the illumination of each respective diode of the pair
is equal.
Referring now to Figure 3, there is shown a portion of the
array 45 of X and Y coordinate addressing indicia. The indicia
59 co~prise, for example, square dots of chromium plating on a
fused silica plate 61. A border 62 D* chromium plating surrounds
the array 45 of addressing indicia 59, ~k~ are arranged in rows
and columns along the X and Y axes, respectively. The X coordinates
of the array 45 of addressing indicia S9 ~mprise the columns, and the Y
coordinates comprise the rsws, rhus, ea~h addressable po~ition
of the work stage 24 of Pigure 2 is defined by a given indicium
59 having a column n~er corresp~nding to the number of he X
coordinate columns from the left-hand side of the bordex 62 (which
is aligned with the Y a~cis) to that indicium and a row n~nber
corresponding to the number of Y cDordinate rows from th~ front
side of the border (which is aligned with ~he X axis) to that
indicium. In a typical example, the indicia 59 are 10 microns
square located on 20 micron centers along both the X and Y axes.
Referring now to both Fiyures 2 and 3, the sensing window
. .
-13-
~L'7:~5~
plate 52 includes column and row recognition windows 53 which are
of generally two kinds. A first kind of these windows is a trans-
parent rectangle having a width of 1300 microns and a length of
1560 microns for viewing a magnified image of a rectangular area
of 100 microns by 120 microns o:E the array 45 of addressing
indicia 59 (this area corresponds to the space occupied by a Sx6
sub-array of addressing indicia 59). Each window of this first
kind is paired with a window of the second kind comprising an
array of eight parallel, elongated transparent slots having a
center-to-center spacing of 260 microns corresponding to a magni-
fied image of ~he 20 micron center to-center spacing of the ad-
dressing indicia 59. Six o~ these slots have a width of 130 microns
and a length of 2080 microns for. viewing a magnified image of a
rectangular area of 10 microns.by 160 microns of the array 45 of
addxessing indicia 59, and the remaining two slots have a width of
130 microns and a length of 1560 microns for viewing a magnified
image of a rectangular area of 10 microns by 120 microns of the
array of addressing indicia. This permits an image of eight or
six addressing indicia 59 to be observed through each of these
respective types of slots of each window of the second kind. Thus,
each window of the second kind permits a magnified image of sixty
addressing indicia 59 to be observed, whereas each window of the
first kind permits a magnified image of thirty addressing indicia
to be observed (i.e., permits illumina~ion from thirty indicia to
pass therethrough). However, both types of windows are of equal
transparent area. Thus, the output from each of the pairs 57
or 58 of diodes 55 connected in bucking relation will be
zero or a null when the sensed magnified images of the
addressing indicia 59 disposed in a column or row aligned
parallel to the slots of one of the windows of the second
-14-
~IILZ~ 7
kind are half covered by the opaque spacing between those
slots (i.e., when a margi.~al ~dge of each of those slots falls
along the center points of the ~ensed magnified images of the
addressing indicia of each such col~nn or row). It should be
not~d that the slots of the windows of the second kind are elongated
in a direction normal to the direction being sensed ( i . e ., the
~lots of a column recognition window of the second kind are oriented
along the Y axis and the slots of a row recognition window of the
second kind are oriented along the X axis). -
~
Each X or Y coordinate sensin~ diode pair 57 or 58 producPs a ~-
an~ular output current waveform 50 or 60 of the type shown in Figure 4 as
the work stage 24 is moved. Each cy~le of each triangl~lar output
i current waveform 50 or 60 corresponds to the counting of a given
X coordinate column or Y coordinate row of the array 45 of addres-
sing indicia 59 depending.~pon whether the waveform is produced
by an X or a Y coordinate sensing diode pair 57 or 58, respectively.
The two window pairs of the sensing window plate 52 which
correspond to the two X coordinate s~n~ing diode pairs 57 of the
~ensing diode plate 56 are offset relative to one another along
20 the X axis by an amount equal to one fourth of the magnified image of
the 20 micron center-to-center spacing of the addressing indicia
59 as projected onto the sen~ing window plate (i.~., 65 microns~.
This offset results in a 90 sp~cial o~fset in the tri~ar outDut
current waveforms 50 and 60 produced by the two X ~ r~te sensing
diode pairs 57 when ~he~X coordinate of the array 45 of addressing
indi~:ia 59 i~ ~eing sensed. As shown in Figure 4, when the work
stage 24 is ~eing advanced in the positive X direction along the
X axis the triangular output current waveform 50 produ~ed by a
first X coordinate sensing diode pair 57 will lead ~he other tri-
angular output current wavefonm 60 produced by the second X
-15-
7~S7
c~oxdinat~ sensing diode pair 57, whereas when the work stage is
being advanced in the negative X direction along the X axis, the
riangular output ~urrent waveform 60 will lead the triangular
~utput current waveform 50.
Similarly, the two window pairs of the sPnsing window plate
52 which correspcnd to the ~wo Y coordinate sensing diode pairs
58 of the sensing diode plate 56 are offset along the Y axis by
an amoun~ equal to one fo~rth of the magnified image ~f the 20 micron
center-to-center spa~ing of the addressing indicia 59 as projected
onto the sensing window plate (i.e., 65 microns). This provides a 90
spacial offset similar to that shown in Figure 4 in the triangular
~utput current waveforms 50 and 60 produced by the two Y eoordinate
sensing diode pairs58whenthework stage 24 is being advanced along
the Y axis to sense the Y coordinate of the array 45 of addressin~
indicia. The triangular output current waveform 50 produced by a first
Y coordinate sensing diode pair 58 will either lead or lag the
triangular output ~T~wa~Dxm60pr~redbythe second Y coordinate
sensing diod~ pair 58 depending on whether the work stage 24 is
being advanced in the positi~e or the negative direction, r.espec-
tively, along the Y axis.
Referring now spe~ifically to Figure 2, the triangular outputcurrent waveforms 50 and 60 from the two X coordinate sensing
diode pairs 57 are applied to respective amplifiers and wave
~hapers 65 ~oupl~d to an X counter 68. Similarly, the triangular
output current waveforms 50 and 60 from the two Y coordinate
uen~in~ diode pairs ~8 are applied to resp~ctive amplifiers and
wave shapers 66 coupled to a Y counter 69. The ampliiers and
wave shapers 65 produce quare wave signals 50' and 60' of the
type ~hown in Figure 5 from the respective triangular output
current waveforms 50 and 60 pplied thersto, and the amplifiers
-16- .
~L7;2S7
and wave shapers 66 al30 produce such square wave signals 50' and
60' from the respo~ctive triangular output current waveforms 50
and 60 applied thereto. Thus, there is one square ~ave pulse per
X coordinate col~mn or Y covrdinate row of addressing indicia
~en~ed by the sensing window plate 52 ahd sensing diode plate 56.
the sq~are w~rve signals S0' and 60' from ~e a~lifiers and wave shapers
65 or 66 are de~ived frcm a leading trianguLlr ou~ut current waveform
50 (produced by the first X or Y coordinate sensing diode pair
57 or 58) and a lagging triangular output current waveform 60
(produc~d by the second X or Y coordinate sensing diode pair 57
or 58), as when the work stage 24 is being advanced in the posi-
tive X or Y direction along the X or Y axis (i.e., when ~he square
wave signal 50' leads the square wave signal 60' as shown in
Fiyure 5), the respective X or Y counter 68 or 6-9 is latched for
counting X coordinate columns or Y coordinate rows of addressing
indicia in a positive direction producing a positive count. Simi-
larly, when the square wave signals 50' and 60' are derived from
a lagging triangular outpu~ current waveform 50 and a leading
triangular output current waveform 60, as when the work s tage 24
20 is being advanced in the neyative direction along the X or Y axis
( i . e ., when the square wave signal 50 ' lags the square wave signal
60'), the respective X or Y counter 68 or 69 is latched for
counting X coordinate columns or Y coordinate rows of addressing
indicia in a negative direction producing a negative count. The
outputs of the X and Y c~ounters 68 and 69 are applied to respective
~rror detectors ~1 and 72 for comparison with X and Y coordinate
reference address inputs derived from the programmer 73, which
i~ programmed by the opsra~or.to select predetermined address
positions of the wor~ stage 24 (and, hence,of the wafer 30 held
30 thereby). Error outputs derived from the respective error
7~57
detectors 71 and 72 are ap~lied tD the inp~ts of respective servo
amplifiers ~ and 7;, the outputs of which are applied to the respec-
tive X and Y servo motors 76 and 77 for driving the work stage 24
in such a direction as to cause the error output5 from the error
detectors to go toward zero.
The progr~mmer.73 keeps track of the coun~ed number of X
coordinate columns and Y coordinates rows of addressing indicia
and of the remaining number of X coordinate columns and Y coordinate
rows to reach the X and Y coordinates of the desired reference
address (i.e., the addressed position of the work stage 24) and
controls the rate at which the X and Y servo motors 76 and 77
move the work stage so that certain predetermined acceleration
and deceleration limits are not exceeded. For example, the pro-
grammer 73 controls the acceleration and deceleration to one
tenth of a G lthe force of gravity)~ Whe~ the error output from
the error detector 71 is within one X coordinate column of the X
coordinate of the addressed posïtion of the work stage 24, the
programmer 73 sets a switch S~ for applying the output of the first
X ~oordinate sensi~g diode pair 57 to an analog servo amplifier
81. Similarly, when the error output from the error detector 72
is within one Y coordinate row of the Y coordinate of the addressed
position, the programmer 73 sets another switch Sy for applying
the output of the first Y coordinate sen~ing diode pair 5~ to
another analog servo amplifier 82. The outputs of the analog
~ervo amplifiers ~l and ~2 are applied to the inputs of the respec-
tive Bervo amplifiers 74 and 75 for causing the respective X and
Y servo motors 76 and 77 to lock the worX stage 24 in place (rela-
tive to the sensor stage 46) at respective X and Y coordinates
corresponding to the respective crossovers 83 of the respective
portions of the respective trian~ular output waveforms 50 applied
.
-18-
7257
to the respective analog servo amplifiers 81 and 82 as shown in
Figure 6~ Each such crossover ~3 corresponds to the center of a
: 10 micron wide region of the workpiece in the X or the Y direction
and is precisely determined and repeatable with an error of less
than one tenth of a micron. Thus, the worX stage 24 (and, hence,
a wafer 30 held thereby) can be programmed to move to any selected
on~ of a nu~ber of addressable positions spaced at 20 micron
intervals along both the X and Y axes. In addition, these addres-
sable positions can be repeat~bly addressed to within one tenth
of a micron.
In addition, each addressed position of the work stage 24 can
be interpolated ~i.e., changed relative to a fixed position on the
granite block~ plu or minus 20 microns along both the X and Y
axes by producing a relatively slight displacement of the sansor
stage 46 (which otherwisa remains stationary) and, hence, of the
work stage (once the work stage is locked in place relative to
the sensor stage so as to move therewith) relative to the granite
block. More particularly, the sen or stage 46 ~including the
sensing window plate 52) is displaoeable along both the X and Y
axes by means of X and Y servo mbtors 84 and BS.
These servo motors are controlled by error signals fro~ respective
X and Y error de~ectors 86 and 87~ The output of an X displace-
ment linaar variable differential transformer 88 and the ou~put
of a Y displacement linear variable differential transformer 89
~both of which transfor~ers are fixedly referenced to the granite
block for dete~tion of X and Y displacements of the ~ensor stage
~6) are ap~lied to the respective X and Y error detectors 86 and
87 for comparison with respective reference signals derived from
respective X and Y reference potenti~meters 91 and 92 under the
control of the operator. The error signals from error detectors
-19~
7~S~
86 and 87 are amplified by respective servo æmplifiers 93 and 94
and applied to the r~spective ~ and Y Ber~o m~ors ~4 and 85. Thus, the
X and Y reference potenti~meters 91 and ~2 permit interpolation
of the X and Y coordinates of the addressed position o the work
tag~ 24 to better than one tenth of a micron along both the X
anl3 Y axas.
In a totally automated system the interpolation set~-ings of
the X and Y reference potentiometers 91 and 92 and, hence,the r~ce
signals derived ~rom those potentiometers for comparison with
the outputs of the X and Y displacement linear variable differ-
ential transformers 88 and 89 in interpolating the X and Y
coordinates of the addrPssed position, could be selected by the
programmer 73. However, in a preferred embodiment of a step-and-
rep at alignment and exposure machine 20, such as that shown in
Figures 1 and 2, for aligning the pattern bearing surface of the
mask 98 and an image of a selected addressed region 99 of the
upper surface of the wafer 30, it is particularly advantageous
for the operator to have control over the interpolation settings
of the X and Y reference potentiometers 91 and 92 as will become
apparent below.
The addressed region ~9 of ~he upper surface of the wafer 30
is illuminated by light directed from a lamp 101 to an illumina-
tion projection lens 102 and thence to a beam splitting mirror 103
fr~m which it is reflected ~hrough the projection lens 104 onto
the addressed region uf the upper surface of ~he wafer. An image
of the illuminated addr~ssed region 99 of the upper ~urface of
the wafer 30 is projec~ed back through the projection lens 104
onto the back side of the mask g8 for viewing with the pattern
of ~he mask through the microscope 105. Thus, the operator is
able to observe through the microscope 105 a portion lD6 of the
-20-
~z~s~
pattern of the mask 98 (i e., that portion falling within the
field of the microscope~ an~ a eorresponding portion of the image
of the illuminated region 99 of the upper surface of the wafer 30.
In cases where the wafer 30 h~s been through one or more
steps in its processing, an image of a circuit pattern formed on
the illuminated addressed region 99 of the upper surface of the
wafer is ob~ervable with the pattern of the mask 98 through the
microscope 105. The pattern of the mask 98 and the image of the
circuit pattern of the wafer can be brought into precise alignment
by obsexving them through the microscope 105 while adjusting the
interpolating ~ettings of the X and Y reference potentiometers 91
and 92 to align them to within better than one tenth of a micron.
This precision i~ obtainable because the masX 98 is stationary rela-
tive to the granite block while the wafer 30 and, hence, the image
of the illuminated addressed region 99 of the wafer are m~ved rela-
tive to the mask and the granite block with the work stage 24,
which is locked by the X and Y servo motors 76 and 7Z as described
above,for movement with the sensor stage 46.
The interpolated addressed region 99 of the wafer 30 is then
exposed in accordance with the pattern of the mask 98 by employing
the projection light source 29 of Figure 1 to illuminate the pat-
~rn of the mask and by proje~ting an image of the illuminated
pattern of the mask through the projection lens 104 onto the
region 99 of the wafer. Following this exposure operation, the
interpolated (or zeroed)~ addressed position of the work ~tage 24
is used as a reference position from which the pro~rammer 73
automatically causes the work stage to be sequentially moved to
other predetermined addressed positions so as to saguentially
position other regions of the wafer 30 for expo~ure in accordance
with the pattern of the ma~k 98 (those regions being spaced from
-21-
~725"7
~ach other by predetermined distances related to the size of the
image of the pattern of ~he ~a~ as projected onto the wafer).
The step-and-repeat alignment ~nd exposure machine 20 of Figur~s
1 and 2 thus permits adjustments to be made in the addressed
position of the work stage 24 in order to compensate for slight
errors in the positloning of the wafer 30 on the work stage by
the automatic wor~piece handling unit 28 during the wafer loading
operation.
As previously described with reference to Figures 2 and 3,
an image of an ill~minated region of the array 45 of addressing
indicia 59 is projected onto the sensing window plate 52 of the
sensor stage 46. This is done in ~uch a manner that the front
side of the border 62 (which is aligned with the X axis and employed
as a reference for the Y coordinate rows of addressing indicia 59
and which is disposed closest to the reader in the orientation of
Figure 2) is projected onto the ~ensing window plate 52
along ~he far side thereof rom the reader. Similarly, the
left-hand ~ide of the border 62 (which i5 aligned with the Y axis
and employed as a reference for the X coordinate eolumns of addres-
sing indicia 59) is projected onto the sensing window plate 52along the right-hand side thereof. Border sensing windows 114
and llS of the ~ensing window plate 52 and corresponding dio~es
116 and 117 of the sensing diode plate 56 are arranged for sensing
~he respe~tive Y and X reference sides of the border 62. The
~ignals produced by the ~ respective diodas 116 and 117 ( as shown
in Figure 7 for one of the diodes) are each applied (as shown in
Figure 8 for the diode 116) to a respective amplifier 118 for
amplification and thence to one input of a respective threshold
detector 719 for compari~on with a reference signal derived from
a respective referenoe potentiometer 120 and applied to another
-22-
~2~7~25~
input of the threshold detector. The output of each threshol.d
detector 119 is applied to the programmer 73 Isuch as a Texas
Instrument 16 bit Model ~9900 microprocessor) to indicate the
crossing of the respective Y or X r~ference sides of the border 62.
More particularly, the signal level I produced by each diode
116 or 117 is shown:in Figure 7 as a func~ion of the position of
the respective border sensing window 114 or 115 relative to the
image of the illuminated region of the array ~5 of addressing
indicia 59 projec~ed thereon. When the border sensing window 114
10 or llS is disposed entirely within a portion of that image con-
taining only the addressing indicia 59, which provide a reflectivity
coefficient of approximately 25 percent, the signal level I pro-
duced by the corresponding diode 116 or 117 is at 25 percent of
full scale. ~owever, as a portion of that image containing a
portion of ~he border 62, which has a reflectivity coefficient of
100 percent, moves across the border sensing window 114 or 115,
the signal level I produced by the corresponding diode 116 or 117
begins to in~rease as ~he image of that portion of the bord~r
begins to oover khe border sensi~g window. When the image of that
portion of the border 62 completely covers the border sensing
window 114 or 115, the signal level I produced by the corresp~nding
diode 116 or 117 i-~ at 100 pereent of full scale. Each threshold
dete~tor 119 is set 80 that a signal level corresponding ~o five
eighths of full scale (5/8 Iloo% as shown in Figure 7) triggers
the threshold detector to provide an output indicating the sensinq
of the border 62.
When th~ step-and-repeat alignment and exposure machine 20
of Figures 1-3 i5 turned on, the programmer 73 causes ~h~ work
3tage 24 to be moved ~o that ~he s~nsor stage 46 senses the X and
30 Y r~ferenc~ ~ides of t:he border 62 en~losing the array 45 of X
-23-
~2~7;i~
coordinate columns and Y coordinate rows of addressing indicia 59
and so that the X and Y counters 68 and G9 are set to reference
the X coordinate column and Y coordinate row counts to the respec-
. ti~ X and Y refer~nce ~ideQ of the ~order. More particularly,the X referenoe ~ide of the border 62 is s~nsed by the programmer
73 causing the work stage 24 to be moved in the negative direction
along the X axis, while maintaining a~ initial Y coordinate addxess,
until such time as an image of the X reference side of the border
is detected by border sensing window 115, the corresponding diode
117, and the corresponding thr~shold detector 119 (see Figure 8)
as described above. The output of the corresponding threshold
detector 119 is applied to the programmer 73 for referencing the
X coordinate oolumn count of the X counter 68 to the respective
X r~ferenc~ side of the border 62. The programmer 73 then causes
the work stage 24 to be moved in the positive direction along tne
X axi~, while maintaining the initial Y coordinate addr~ss, until
such time as th~ X count0r 68 has counted to the center X coor-
dinate column of the array 45 of addressing indicla 59. The pro-
grammer then causes the wo~k s~age 24 to be moved in the negative
direction along the ~ axis, while maintaining the oenter X coor
dinate address, until such time as an image of the Y reference
side o~ th~ border 62 is detected by the border sensing window 114,
~he corresponding diode 116, ~nd the corresponding thre hold detector
119. The output of the correspondi~g threshold detector 119 is
~pplied to the programmer 73 for referen~ing the Y coordinate row
~ount of the Y counter 69 to the respective Y reer~nce side of
the border 62.
It should be noted that ~he first ~nsing diod~ pair 57,
which is employed with the ~witc~ S~ and the analog servo amplifier
81 in lo~kiny the work ~tage ~4 in pla~e (relative to the sensor
-24-
7~
stage 46) at ~he X coordinate of the addressed p~sition, as pre-
viously descri~ed with re~erence to Figur~s 2-4 and 6, comprises
the sensing diode pair 57 furthest fr~m the diode 116 employed
for ~ensing the Y reference side of the bord~r 62. This permits
the ~ensor stage 46 to be ~fficien~ly employed both in sensing the
Y ref~renc~ side uf.the border 62 and in stopping the mov~ment of
the work ~tage 24 and locking it in place at the X coordinate of
the addressed p~sition. For similar reasons, the sensing diode
pair 58, which i~ employed with the switch Sy and the analog servo
10 amplifier 82 in locking the work stage 24 in place at the Y coor-
dinate of the addressed position, similarly comprises the sensing
diode pair ~8 furthest from the diode 117 employed for sensing
the X reference side of the bordex 62.
The above-described X-Y addressable workpiece positioner and
step-and-repeat alignment and ~xposure machine 20 using same have
the advantage of p~rmi~ting the work stage 24 and, hence, a work-
piece held thereby to be stepped sequentially to addressable p~si-
tions precisely determinable to better than one tenth of a micron.
The st~pping of the work ~tage 24 and, hence, the workpiece held
thereby from one addressable position to the next is accomplished
by mov~ment of the work stage and the wor~piece along a path which
is the shortest distance between ~hose two addressed positions
and which is pr~cisely defined by a common two-dimensional array
45 o~ X and Y coordinate addressing indicia. This shortens the
~t~pping time and increase-~ the t~Lghput of the machine. More-
over, the accuracy o~ the addressed po~itions is precisely deter-
min~d by the precise positioning of th~ X and Y coordinate addressing
indicia rather than being dependent upon the precision of the
orthogonality of costly bearing a~semblies or upon laser inter-
3C ferometers requiring environmentally controlled chambers.
-25
~Z~72~7
As used herein, a "tw~dimensional array" OI' addressing
indicia shall be defin2d to include indicia arrayed ( i - e ., serialized)
in two dir~ctions. Thu5, a series of parallel lines is a one-
dimensional array, whereas a series of dots serialized in ~wo
directi~ns, a~ in ~igure! 3, cçrnprises a ~wo-dimensional array.
