CA1217257A

CA1217257A - X-y addressable workpiece positioner having an improved x-y address indicia sensor

Info

Publication number: CA1217257A
Application number: CA000488277A
Authority: CA
Inventors: Edward H. Phillips
Original assignee: Optimetrix Corp
Current assignee: Optimetrix Corp
Priority date: 1980-03-27
Filing date: 1985-08-07
Publication date: 1987-01-27
Also published as: CA1198797A

Abstract

ABSTRACT
In an X-Y addressable workpiece positioner, the workpiece to be positioned, such as a semiconductive wafer to be sequentially exposed at different regions thereof in accordance with a pattern of a mask, is disposed for movement with a work stage along coordinate X and Y axes. The work stage has a two-dimensional array of X and Y coordinate addressing indicia enclosed within a border and affixed to the work stage for movement therewith.
A portion of an enlarged image of the array of addressing indicia is projected onto a sensor stage to derive an output indicative of the X and Y coordinates of the array of addressing indicia relative to the position of the sensor stage. The X and Y coor-dinates of the array of addressing indicia are sensed through addressing indicia recognition windows of the sensor stage and are differentially compared to remove unwanted background effects.
Concomitantly, the border is sensed through border sensing windows of the sensor stage to provide a frame of reference for the sensed X and Y coordinates of the array of addressing indicia. The sensed X and Y coordinates of the array of addressing indicia are compared with the X and Y coordinates of a selected addressed position of the work stage to derive an error output. In response to this error output the work stage is moved to the selected addressed position so as to position a region of the workpiece for exposure in accordance with the pattern of the mask. The work stage is sequentially moved to succeeding addressed positions in the same manner to position each of the remaining regions of the workpiece for exposure in accordance with the pattern of the mask.

Description

~ 2 ~ ~
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

-2-~ ~ ~ r~

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.

L7Z5~

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:

~ ~ ~ 7 ~ ~

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 ~.2~.~2st~

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.

l7~

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 L7Z5'~

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;
.

~2~ i7 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 7;~
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 -9a-~ ~ 72~i7 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 -9b-~ lL2~7~5~7 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 --gc--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 -9d-~ ~7 ~ ~

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 -9e-~ ~4 ~ ~ r~

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 -9:~-~72~i7 ~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 _ 9~

~ 2 ~ 7 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, -9h-Lt7~S7 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 -9i-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 _9j_ ~ 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.

. -9k-2~i~

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 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).

-lOa-~Z~7Z57 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 ~ ~ ~ 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 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 . .

~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 ~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

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 .

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 ~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 ~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 ~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

~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 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.

~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.

Claims

CLAIMS:

1. 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 within 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 different position in response to the error output.

2. A method as in claim 1 wherein each window of each pair of pattern recognition windows has a transparent area equal to that of the other window of the same pair.

3. A method as in claim 1 or 2 wherein one window of each pair of pattern recognition windows includes an array of parallel transparent elongated regions with the axis of elongation of those regions being orthogonal to the direction in which the respective X or Y coordinate positioning indicia are sensed thereby.

4 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 within 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 and provided with X and Y border indicia for referencing the X and Y coordinate positioning indicia, respectively;
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 for sensing the X
and Y coordinate positioning indicia of the enlarged image to derive an output determinative of the X and Y
coordinates of the position of the work stage;
moving 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 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 different position in response to the error output.

5. A method as in claim 4 wherein:
said array of X and Y coordinate positioning indicia comprises an array of dots having an optical transmission or reflectance coefficient of a first value;
said X and Y border indicia have an optical trans-mission or reflectance coefficient of a second value; and each of said X and Y border indicia is sensed by detecting an optical transmission or reflectance coefficient of a value intermediate the first and second values.

6. An X-Y addressable workpiece positioning method comprising the steps of:
coupling the 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 within 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 and provided with X

and Y border indicia for referencing the X and Y
coordinate positioning indicia, respectively;
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;
moving 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 respective X and Y border sensing windows, and referencing the sensed X and Y coordinate positioning indicia to the sensed X and Y border indicia, respectively, the X and Y
border sensing windows being located in the sensor stage closer to the respective 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 recognition windows to be employed for sensing the X and Y 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.

7. A method as in claim 6 including the additional steps of:
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 different position in response to the error output.

8. An X-Y addressable workpiece positioning apparatus 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;
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 coordinate 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;

the sensor stage means including at least two pairs of pattern recognition windows and corresponding sensing means for independently 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 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 work 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.

9. Apparatus as in claim 8 wherein each window of each pair of pattern recognition windows has a trans-parent area equal to that of the other window of the same pair.

10. Apparatus as in claim 8 or 9 wherein one window of each pair of pattern recognition windows includes an array of parallel transparent elongated regions with the axis of elongation of those regions being orthogonal to the direction in which the respective X or Y coordinate positioning indicia are sensed thereby.

11. An X-Y addressable workpiece positioning apparatus 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 work stage means and movable therewith for effecting positioning of the work stage means, and X and Y border indicia for referencing the X and Y coordinate positioning 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 enlarged image of at least a portion 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;
drive means for moving the work stage means so that the X and Y border indicia of the enlarged image may be sequentially sensed by the sensor stage means and the sensed X and Y coordinate positioning indicia referenced to the sensed X and Y border indicia, respectively, to determine the X and Y coordinates of the position of the work stage means; and comparative means for comparing the X and Y coor-dinates of 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.

12. An apparatus as in claim 11 wherein:
said array of X and Y coordinate positioning indicia comprises a two-dimensional array of dots having an optical transmission or reflectance coefficient of a first value;
said X and Y border indicia have an optical transmission or reflectance coefficient of a second value; and said sensor stage means senses the X and Y border indicia of the enlarged image by detecting an optical transmission or reflectance coefficient of a value inter-mediate the first and second values.

13. An X-Y addressable workpiece positioning apparatus 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;
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 coordinate positioning indicia affixed to the work stage means and movable therewith for effecting positioning of the work stage means, and X and Y border 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 enlarged 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 independently 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 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, and a pair of X and Y 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 indicia of the enlarged image than the 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 the enlarged image; and comparative means for comparing the X and Y coordinates of 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.

14. An addressable workpiece positioner comprising:
stage means for holding a workpiece, the stage means being movable along a pair of coordinate axes to addressable coordinate positions in a plane containing those axes and having a two-dimensional array of coordinate addressing indicia affixed thereto for movement therewith;
sensor means for determining the addressable coordinate position of the stage means;
optical means for projecting an image of a portion of the array of coordinate addressing indicia onto the sensor means;
the sensor means including at least two pairs of sensing means for sensing the coordinate addressing indicia of the image to determine the addressable coordinate position of the stage means;
compensating means, including each pair of sensing means, for compensating for undesired variations in the intensity of the image;
control means for comparing the addressable coordinate position of the stage means with another addressable coordinate position to derive an error signal, and drive means for moving the stage means and the array of coordinate addressing indicia to said other addressable coordinate position in response to the error signal.

15. An addressable workpiece positioner as in claim 14 wherein each pair of sensing means comprises:
a transparent window of a first kind communicating with a corresponding first sensing element; and a transparent window of a second kind communicating with a corresponding second sensing element and having a transparent area equal to that of the window of the first kind.

16. An addressable workpiece positioner as in claim 15 wherein:
each window of the first kind comprises a group of parallel transparent elongated regions each having an axis of elongation parallel to the respective columns or rows of addressing indicia sensed thereby, having a width equal to that of each respective column or row of addressing indicia sensed thereby, and having a length equal to that of an integer multiple of the center-to-center spacing of the respective columns or rows of addressing indicia sensed thereby; and each window of the second kind comprises a single transparent region having one or more rectangular areas of a width and a length equal to an integer multiple of the center to-center spacing of the respective columns or rows of addressing indicia sensed thereby.

17. An addressable workpiece positioner as in claim 16 wherein the optical means includes a magnifying lens for enlarging the image protected onto the sensor means.

18. An addressable workpiece positioner as in claim 17 wherein the first and second sensing elements of each pair of sensing means are connected in bucking relationship.

19. An addressable workpiece positioner as in claim 14 wherein the sensor means includes four pairs of sensing means.

20. An addressable workpiece positioner as in claim 19 wherein each pair of sensing means comprises:
a transparent window of a first kind communicating with a corresponding first sensing element; and a transparent window of a second kind communicating with a corresponding second sensing element and having a transparent area equal to that of the window of the first kind.

21. An addressable workpiece positioner as in claim 20 wherein:
each window of the first kind comprises a group of parallel transparent elongated regions each having an axis of elongation parallel to the respective columns or rows of addressing indicia sensed thereby, having a width equal to that of each respective columns or row of addressing indicia sensed thereby, and having a length equal to that of an integer multiple of the center-to-center pacing of the respective columns or rows of addressing indicia sensed thereby; and each window of the second kind comprises a single trans-parent region having one or more rectangular areas of a width and a length equal to an integer multiple of the center-to-center spacing of the respective columns or rows of addressing indicia sensed thereby.

22. An addressable workpiece positioner as in claim 2 wherein the optical means includes a magnifying lens far enlarging the image projected onto the sensor means.

23. An addressable workpiece positioner as in claim 22 wherein the first and second sensing elements of each pair of sensing means are connected in bucking relationship.

24. An addressable workpiece positioner as in claim 19 wherein:
the coordinate axes comprise orthogonal first and second axes;
the array of coordinate addressing indicia comprises coordinate addressing indicia of uniform size uniformly arrayed in rows parallel to the first axis and in columns parallel to the second axis;
two of the pairs of sensing means are offset from one another along the first axis for sensing columns of coordinate addressing indicia of the image to determine the addressable coordinate position and the direction of movement of the stage means along the first axis; and two of the pairs of sensing means are offset from one another along the second axis for sensing rows of coordinate addressing indicia of the image to determine the addressable coordinate position and the direction of movement of the stage means along the second axis.

25. An addressable workpiece positioner as in claim 24 wherein each pair of sensing means comprises:
a transparent window of a first kind communicating with a corresponding first sensing element; and a transparent window of a second kind communicating with a corresponding second sensing element and having a transparent area equal to that of the window of the first kind.

26. An addressable workpiece positioner as in claim 25 wherein:
each window of the first kind comprises a group of parallel transparent elongated regions each having an axis of elongation parallel to the respective columns or rows of addressing indicia sensed thereby, having a width equal to that of each respective column or row of addressing indicia sensed thereby, and having a length equal to that of an integer multiple of the center-to-center spacing of the respective columns or rows of addressing indicia sensed thereby; and each window of the second kind comprises a single transparent region having one or more rectangular areas of a width and a length equal to an integer multiple of the center-to-center spacing of the respective columns or rows of address-ing indicia sensed thereby.

27. An addressable workpiece positioner as in claim 26 wherein the optical means includes a magnifying lens for enlarging the image projected onto the sensor means.

28. An addressable workpiece positioner as in claim 27 wherein the first and second sensing elements of each pair of sensing means are connected in bucking relationship.

29. An addressable workpiece positioner comprising:
stage means for holding a workpiece, the stage means being movable along a pair of coordinate axes to addressable coordinate positions in a plane containing those axes;
sensor means for determining the addressable coordinate position of the stage means;
the stage means including indicia means affixed thereto for movement therewith to effect coordinate positioning of the stage means, the indicia means including coordinate reference indicia and a two-dimensional array of coordinate addressing indicia;
optical means for projecting an image of a portion of the indicia means onto the sensor means;
the sensor means including first sensing means for sensing the coordinate reference indicia of the image, and second sensing means for sensing the coordinate addressing indicia of the image with reference to the sensed coordinate reference indicia to determine the addressable coordinate position of the stage means;
control means for comparing the addressable coordinate position of the stage means with another addressable coordinate position to derive an error signal; and drive means for moving the stage means and the indicia means to said other addressable coordinate position in response to the error signal.

30. An addressable workpiece positioner as in claim 29 wherein:
the coordinate axes comprise orthogonal first and second axes;
the coordinate reference indicia comprise first and second border portions of a border enclosing the array of X
and Y coordinate addressing indicia with the first border portion being parallel to the second axis and with the second border portion being parallel to the first axis;
the coordinate addressing indicia are arrayed in rows parallel to the first axis and in columns parallel to the second axis; and the stage means and the indicia means may be sequentially moved to a first addressable coordinate position at which one the first and second border portion of the image may be sensed by the first sensing means while coordinate addressing indicia of the image are sensed by the second sensing means and to a second addressable coordinate position at which the other of the first and second border portions of the image may be addressed by the first sensing means while the coordinate addressing indicia of the image are sensed by the second sensing means.

31. An addressable workpiece positioner as in claim 29 wherein:
the array of coordinate addressing indicia has an optical reflectance or transmission coefficient of a first value, the coordinate reference indicia have an optical reflectance or transmission coefficient of a second value; and the first sensing means senses the coordinate reference indicia by detecting an optical reflectance or transmission coefficient intermediate the first and second values.

32. An addressable workpiece positioner as in claim 31 wherein:
the coordinate axes comprise orthogonal first and second axes;
the coordinate reference indicia comprises first and second border portions of a border enclosing the array of X
and Y coordinate addressing indicia with the first border portion being parallel to the second axis and with the second border portion being parallel to the first axis;
the coordinate addressing indicia are arrayed in rows parallel to the first axis and in columns parallel to the second axis; and the stage means and the indicia means may be sequentially moved to a first addressable coordinate position at which one of the first and second border portions of the image may be sensed by the first sensing means while coordinate addressing indicia of the image are sensed by the second sensing means and to a second addressable coordinate position at which the other of the first and second border portions of the image may be sensed by the first sensing means while the coordinate addressing indicia of the image are sensed by the second sensing means.

33. An addressable workpiece positioner as in claim 29 wherein the optical means includes a magnifying lens for enlarging the image projected onto the sensor means.
34. An addressable workpiece positioner as in claim 33 wherein:
the coordinate axes comprise orthogonal first and second axes;
the coordinate reference indicia comprise first and second border portions of a border enclosing the array of X
and Y coordinate addressing indicia with the first border portion being parallel to the second axis and with the second border portion being parallel to the first axis;
the coordinate addressing indicia are arrayed in rows parallel to the first axis and in columns parallel to the second axis; and the stage means and the indicia means may be sequentially 33 An addressable workpiece positioner as in claim 29 wherein the optical means includes a magnifying lens for enlarging the image projected onto the sensor means.

34. An addressable workpiece positioner as in claim 33 wherein:
the coordinate axes comprise orthogonal first and second axes;
the coordinate reference indicia comprise first and second border portions of a border enclosing the array of X
and Y coordinate addressing indicia with the first border portion being parallel to the second axis and with the second border portion being parallel to the first axis;
the coordinate addressing indicia are arrayed in rows parallel to the first axis and in columns parallel to the second axis; and the stage means and the indicia means may be sequentially moved to a first addressable coordinate position at which one of the first and second border portions of the image may be sensed by the first sensing means while coordinate addressing indicia of the image are sensed by the second sensing means and to a second addressable coordinate position at which the other of the first and second border portions of the image be sensed by the first sensing means while the coordinate addressing indicia of the image are sensed by the second sensing means.

35. An addressable workpiece positioner comprising:
stage means, movable along a pair of coordinate axes, for holding a workpiece to be positioned;
a two-dimensional array of coordinate addressing indicia together with coordinate reference indicia for the array of coordinate addressing indicia, affixed to the stage means, for movement with the stage means;
sensor means for sensing the coordinate addressing indicia and the coordinate reference indicia to provide output information determinative of the coordinate position of the stage means; and control means, responsive to output information from the sensor means and to input control information, for moving the stage means to coordinate positions determined by the input control information.

36. An addressable workpiece positioner as in claim 35 wherein:
said coordinate addressing indicia are uniformly arrayed in rows parallel to one of the coordinate axes and in columns parallel to the other of the coordinate axes;
one of said coordinate reference indicia is disposed parallel to said one of the coordinate axes and adjacent to one side of the array of coordinate addressing indicia; and another of said coordinate reference indicia is disposed parallel to said other of the coordinate axes and adjacent to another side of the array of coordinate addressing indicia.

37. An addressable workpiece positioner as in claim 36 wherein said coordinate reference indicia comprise portions of a border circumscribing the array of coordinate addressing indicia.

38. An addressable workpiece positioner as in claim 37 wherein said coordinate addressing indicia and said coordinate reference indicia comprise reflective regions formed on a transparent plate disposed between the sensor means and the position of the workpiece.

39. An addressable workpiece positioner as in claim 35 wherein said sensor means includes:
addressing indicia sensing means for sensing the coordinate addressing indicia to provide output information determinative of the coordinate position of the stage means; and reference indicia sensing means for sensing the coordinate reference indicia to provide output information for referencing the sensed coordinate addressing indicia.

40. An addressable workpiece positioner as in claim 39 wherein:

said array of coordinate addressing indicia has an optical reflectance or transmission coefficient of a first value;
each of said coordinate reference indicia has an optical reflectance or transmission coefficient of a second value; and said addressing indicia sensing means senses the coordinate addressing indicia by detecting an optical reflectance or transmission coefficient intermediate the first and second values.

41. An addressable workpiece positioner as in claim 39 wherein said stage means may be sequentially moved to a first coordinate position at which one of the coordinate reference indicia may be sensed by the reference indicia sensing means while coordinate addressing indicia are sensed by the addressing indicia sensing means and to a second coordinate position at which the other of the coordinate reference indicia may be sensed by the reference indicia sensing means while the coordinate addressing indicia are sensed by the addressing indicia sensing means.

42. An addressable workpiece positioner as in claim 41 wherein said reference indicia sensing means comprises a pair of transparent windows each communicating with a corresponding photodetector.

43. An addressable workpiece positioner comprising:
stage means, movable along a pair of coordinate axes, for holding a workpiece to be positioned;
a two-dimensional array of coordinate addressing indicia, affixed to the stage means, for movement with the stage means;

said coordinate addressing indicia being uniformly arrayed in rows parallel to one of the coordinate axes and in columns parallel to the other of the coordinate axes;
sensor means for sensing the coordinate addressing indicia to provide output information determinative of the coordinate position of the stage means, said sensing means including at least a first pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in rows parallel to said one of the coordinate axes to provide output information determinative of one coordinate of the coordinate position of the stage means, and at least a second pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in columns parallel to said other of the coordinate axes to provide output informa-tion determinative of another coordinate of the coordinate position of the stage means;
optical means for projecting an image of a portion of the array of coordinate addressing indicia onto the sensor means;
compensating means, including each pair of sensing means, for compensating for undesired variations in the intensity of the image; and control means, responsive to the output information from the sensor means and to input control information, for moving the stage mean to coordinate positions determined by the input control information.

44. An addressable workpiece positioner as in claim 43 wherein each of said pairs of sensing means comprises:
a transparent window of a first kind communicating with a corresponding first photodetector; and a transparent window of a second kind communicating with a corresponding second photodetector and having a transparent area equal to that of the window of the first kind;
said first and second photodetectors of each pair of sensing means being connected in bucking relationship.

45. An addressable workpiece positioning method comprising the steps of:
placing the workpiece to be positioned on a stage that is movable along coordinate axes in a plane containing or parallel to those axes and that has a two-dimensional array of coordinate addressing indicia affixed thereto for movement therewith;
protecting an image of at least a portion of the array of coordinate addressing indicia onto a sensor;
sensing the coordinate addressing indicia through at least two pairs of pattern recognition windows included in the sensor with each pair disposed for independently recognizing and sensing coordinate addressing indicia aligned parallel to a different one of the coordinate axes to derive output information determinative of a different coordinate of the position of the stage and to derive a sensed output through each window of each pair;
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 compensate for undesired variations in the intensity of the image;

comparing the coordinate position of the stage with a designated coordinate position to derive an error output; and moving the stage to the designated coordinate position in response to the error output.

46. An addressable workpiece positioning method as in claim 45 wherein the array of coordinate addressing indicia is provided with border indicia for referencing the coordinate addressing indicia,and the method includes the steps of moving the stage so that the sensor is operable for sequentially sensing the coordinate border indicia; and referencing the sensed coordinate addressing indicia to the sensed coordinate border indicia.

47. An addressable workpiece positioning method as in claim 46 wherein:
the array of coordinate addressing indicia has an optical transmission or reflectance coefficient of a first value;
the coordinate border indicia have an optical transmission or reflectance coefficient of a second value; and each of the coordinate addressing indicia is sensed by detecting an optical transmission or reflectance coefficient of a value intermediate the first and second values.

48. An addressable workpiece positioning method as in claim 45 wherein the last-mentioned step of moving the stage comprises moving the stage to that the sensor is operable for sequentially sensing the coordinate border indicia through respective border sensing windows included in the sensor and disposed closer to the respective coordinate border indicia than the center of each respective pair of pattern recognition windows to as to permit the pairs of pattern recognition windows to be employed for sensing the respective coordinate addressing indicia while the border sensing windows are employed for sensing the respective coordinate border indicia.

49. 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 respectively 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 relative to the work apparatus 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 rows and columns, said reference substrate including a reference strip comprising a reflective band circumscribing said reflective areas, and means for 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 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 first and 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.

50. 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 respectively respon-sive 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 relative to the work apparatus and including a reference substrate carried by one of said stage means and having orthogonal dimension posi-tion related indicia disposed thereupon, said indicia including a plurality of like, rectangularly-shaped opaque surface areas arrayed in orderly rows and columns, said reference substrate including a reference strip comprising an opaque band circumscribing said opaque surface areas, and means for 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 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 first and 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,

51. A servo control system comprising:
stage means movable along orthogonal axes for positioning a workpiece relative to a work apparatus;
first and second drive 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 relative 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 including a plurality of like, rectangularly-shaped reflective surface areas arrayed in orderly rows and columns, said reference substrate including a reference strip comprising a reflective band circumscribing said reflective areas, and means for 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 to 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 to a desired position.

52. A servo control system comprising:
stage means movable along orthogonal axes for positioning a workpiece relative to a work apparatus;
first and second drive 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 relative 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 including a plurality of like, rectangularly-shaped opaque surface areas arrayed in orderly rows and columns, said reference substrate including a reference strip comprising an opaque band circumscribing said opaque surface areas, and means for 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 to 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 to a desired position.