Light exposure device and method

A light exposure device and method for exposing and printing a predetermined pattern on an exposure surface of a substrate comprises measuring means for measuring curvature of the exposure surface of the substrate, a chuck including suck and hold means for sucking and holding a back surface of the substrate opposite to the exposure surface and deforming means for imparting a force to the back surface of the substrate to deform the substrate, and control means for controlling the deforming means of the chuck in accordance with the curvature of the exposure surface of the substrate measured by the measuring means such that the exposure surface of the substrate conforms to an image surface of the pattern over an entire exposure area within a predetermined allowable error.

BACKGROUND OF THE INVENTION 
The present invention relates to a light exposure device and a method for 
exposing a pattern, specifically a semiconductor IC pattern formed by 
photographing technique such as a mask or reticle to a substrate such as a 
silicon wafer, bubble wafer, ceramic substrate or a printed circuit board. 
In forming an LSI pattern on a wafer, it is conventional to apply 
photoresist on the LSI wafer and expose a photomask pattern on the wafer 
to expose the photoresist thereon. 
This process is called lithography and it includes contact method (in which 
exposure is carried out with the mask and the wafer being in contact), a 
proximity method (in which exposure is carried out with the mask and the 
wafer being spaced from each other by several microns to several tens 
microns) and a projection method (in which a pattern on the mask is 
projected onto the wafer). An X-ray exposure device has also been known. 
FIG. 1 shows a construction of a projection type light exposure device as 
an example of the prior art light exposure devices. A pattern 2 indicated 
by an arrow on a surface of a mask 1 is focused to a wafer 4 by an 
exposure light source 3 through a minor optical system comprising a 
concave mirror M.sub.1, a convex mirror M.sub.2 and a plane mirror 
M.sub.3. Numeral 5 denotes an imaged pattern. Periphery of the mask 1 is 
drawn by suction to a carriage 6 by vacuum suction means with a flatness 
of .+-.2 microns. The carriage 6 which carries the wafer 4 and the mask 1 
scans reciprocally as shown by an arrow A so that the mask pattern 2 is 
transferred onto the wafer 4 as the carriage 6 scans. A wafer chuck 7 
forms an air path to link bores formed on the top thereof to a bore 8 
formed at the bottom so that the wafer 4 is drawn to the surface thereof. 
The bore 8 is connected to a vacuum source, not schematically represented, 
through a pipe shown by an arrow 9. FIGS. 2a and 2b show an enlarged 
sectional view and a plan view, respectively, of the wafer 4 mounted on 
the wafer chuck 7. In FIG. 2b, the flatness of the wafer 4 is shown by 
contour lines 10. In the illustrated example, the wafer 4 is spherical and 
protrudes upward. When the surface of the wafer 4 does not coincide with 
an imaging plane 12 of the optical system as shown in FIG. 2a, only a 
portion of a line pattern 13 (FIG. 2b) is transferred because it is imaged 
only to that portion of a wafer surface 11 which lies within a depth of 
focus 14. The depth of focus 14 on the imaging plane 12 is determined by a 
resolution power of the optical system necessary to the transfer, and the 
depth of focus at the resolution power necessary to transfer a line width 
of 3 .mu.m is .+-.5 .mu.m. When this depth of focus is combined with a 
mask positioning error of .+-.2 .mu.m, an allowable depth of focus on the 
part of wafer is .+-.3 .mu.m. When the line width to be transferred is 2 
.mu.m, the allowable depth of focus on the part of wafer is .+-.2 .mu.m. 
On the other hand, the flatness of the wafer surface 11 sucked on the flat 
chuck surface 15 is normally no less than .+-.6 .mu.m, sometimes more than 
.+-.10 .mu.m. This leads to the reduction of the yield. On the other hand, 
the improvement of the flatness of the wafer 4 per se is very difficult to 
attain. 
It has been proposed to focus to the wafer surface 11 in order to image and 
print the mask pattern on a wafer of low flatness. Referring to FIG. 3, 
printing of a circuit pattern on the wafer by the focusing method is 
explained. The wafer 4 is spherical and protrudes upward as in FIGS. 2a 
and 2b and it is assumed that a depth of focus covers two contour lines 
10. When a scan is made in the direction of arrow A (FIG. 1) with a 
printing width W.sub.1 without focusing, the circuit pattern is printed 
only to a ring-shaped area having a width R.sub.0 corresponding to the 
depth of focus. Then, as the scan is made with the same width W.sub.1 
while focusing is made along the center of the width W.sub.1, the pattern 
is printed to the range of R.sub.1. Then, as the scan is made with a 
narrow printing width W.sub.2 three times one for each of three vertically 
divided areas with focusing, the pattern is printed to the range of 
R.sub.3. It is seen from the above explanation that divided exposure is 
best for a high yield. However, when three-division method is used, a 
yield or output is reduced by the factor of three resulting in a 
considerable amount of loss, and a joining of the individual printed 
patterns is very difficult to attain. Accordingly, a high precision 
pattern cannot be attained. Furthermore, complex mechanism and operation 
are required to detect focusing points and adjust focus planes. 
Accordingly, a cost is high and maintenance is difficult and troublesome. 
While the example of LSI has been explained above, the same is equally 
applicable to other substrates (such as magnetic bubble substrate, thin or 
thick film substrate and printed circuit board). 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a light exposure device 
which overcomes the disadvantages in the prior art devices and which 
uniformly exposes a mask pattern over an entire surface of a substrate 
under any condition with the entire surface of the substrate being 
uniformly spaced from the mask surface or aligned to an image plane of the 
mask, so that a yield of a semiconductor device, a magnetic bubble device, 
a thin or thick film circuit device or a printed circuit board is 
enhanced. 
In order to achieve the above object, the present invention is 
characterized by measuring a contour of a curved plane of an exposure 
surface of the substrate and based on the measurement partially and 
vertically fine-adjusting the chuck which holds a back surface of the 
substrate to deform the exposure surface of the substrate to conform to 
the image plane of the mask pattern and exposing the predetermined pattern 
to the deformed exposure surface of the substrate to print the pattern. 
Since the flatness of .+-.2 .mu.m is attained in the light exposure mask 
when the periphery thereof is acted upon by a suction of a vacuum, the 
flatness of the exposure surface of the substrate source (wafer) is 
measured, and based on the measurement, the chuck which holds the back 
surface of the substrate is partially fine-adjusted vertically (in the 
direction of illumination of exposure light) to deform the substrate so 
that the flatness of the substrate which assures a depth of focus not more 
than .+-.3 .mu.m over the entire area of the exposure surface of the 
substrate is attained, and the desired semiconductor IC pattern is exposed 
to the flattened exposure surface of the substrate with a high resolution 
power to print the pattern. 
In an X-ray exposure mask, because the mask is very thin, it is impossible 
to flatten the mask by making it follow the curvature. In addition, the 
light source is a point light source. Thus, in order to attain high 
precision printing, it is necessary to keep a variance of a spacing 
between the surface of the mask pattern and the exposure surface of the 
substrate within approximately .+-.1 .mu.m over the entire exposed area. 
Accordingly, in the X-ray exposure device, it is also very effective to 
partically and vertically fine-adjust the chuck which holds the back 
surface of the substrate or the wafer to deform it so that the spacing 
between the exposure surface of the substrate and the mask pattern surface 
is constant over the entire exposed area. 
In accordance with the present invention, a thin flexible film is disposed 
on the top of the chuck so that the back surface of the substrate is drawn 
to the thin film and a force is applied to the thin film to resiliently 
deform the thin film to thereby deform the substrate. Accordingly, no 
concentrated force is applied to the substrate and the substrate can be 
deformed gently, so that the breaking of the substrate is prevented. 
Furthermore, in accordance with the present invention, by fixing the 
periphery of a circular thin film to the chuck body and arranging 
displacing means at a center thereof to displace it downward, it is 
possible to flatten the convex wafer exposure surface formed by a etching 
process after a lapping process to the flatness not more than .+-.3 .mu.m. 
Thus, the wafer chuck mechanism can be simplified. When an air cylinder is 
used as the displacing means, the control of the air cylinder is 
simplified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to overall schematic view of a light exposure device of the 
present invention in FIG. 4, according to this figure, a substrate or 
wafer 4, on which a semiconductor integrated circuit is formed, is 
arranged on a substrate deformation correcting chuck 16 which has a 
function to correct warp or bend of the substrate 4. The substrate 
deformation correcting chuck 16 is positioned by positioning means (not 
shown) to a carriage 6 which is reciprocally slidable on a base 22 between 
a substrate deformation correcting station C and an exposure and print 
station B. A device 17 for measuring deformation (flatness) on the surface 
of the substrate 4 is mounted at the substrate deformation correcting 
station C. At the substrate deformation correcting station C, deformation 
information (flatness information) of the surface of the substrate 4 
obtained from the substrate deformation measuring device 17 is fed back to 
the substrate deformation correcting chuck 16 to deform the surface of the 
substrate 4 to conform to an image surface of a mask pattern. When the 
image surface of the mask pattern is flat, the surface of the substrate 4 
is also made flat and horizontal. After the above step, the substrate 4 
and the substrate deformation correcting chuck 16 are moved and set in the 
exposure station B, where a light exposure system 21 for exposing a 
pattern of a photomask is located so that the pattern is exposed to the 
substrate 4. More particularly, the light exposure apparatus comprises the 
substrate deformation correcting chuck 16 having one or more displacing 
devices for deforming the wafer or substrate 4 to flatten it with respect 
to a body 38, the deformation measuring device 17, a controller 18 for the 
displacing means, the scanning carriage 6 which carries the substrate 4 
and the mask 1, a magazine 19 for housing cartridges which store the 
substrates 4 printed or to be printed, a transport mechanism 20 for 
transporting a selected substrate between the magazine 19 and the 
substrate deformation correcting chuck 16, the light exposure optical 
system 21 and a base 22. The wafer or substrate 4 which has been 
previously flattened is set on the substrate defromation correcting chuck 
16, and the deformation measuring device 17 detects the deformation such 
as warp or bend of the chucked substrate 4, and the controller 18 
calculates a necessary amount of displacement, which activates the 
displacing device of the substrate deformation correcting chuck 16 to 
deform the substrate 4 to conform to the image surface of the mask pattern 
(which is the imaging plane of the mask pattern in the light exposure 
device, and an imaging plane equally spaced from the mask and the wafer 
over the exposure region in the X-ray exposure device). In the illustrated 
example, since the mask has a high degree of flatness, the substrate 4 is 
flattened. 
The deformation measuring device 17 then checks the flatness and if it is 
not within an allowable range the displacing device is finely vertically 
adjusted a predetermined number of times to repeatedly deform the wafer 4, 
and, when the wafer 4 comes within the allowable range, the carriage 6 is 
moved beneath the light exposure optical system 21 and a stage supporting 
the chuck is moved in X, Y and .theta. (rotation) directions relative to 
the mask 1 to align them to each other while non-exposure light is 
illuminated to an alignment target pattern. After the alignment has been 
attained, the pattern of the mask 1 is printed. The printed wafer or 
substrate is carried to the magazine 19 by the transport mechanism 20. The 
above step is repeated until unprinted substrates are exhausted. 
Preferably, the substrate 4 is deformed to conform to the image plane of 
the mask pattern when it is printed. In the light exposure device, the 
image plane of the mask pattern is flat. If it is sufficiently flat with a 
required accuracy, the substrate 4 is deformed to conform to the flat 
surface. When it is deformed to conform to the image plane, means (not 
shown) for detecting the image plane are required. It may be attained by 
illuminating non-exposure light and detecting the image on the substrate 4 
produced by the mask pattern through the light exposure optical system 21, 
by a detecting optical system (not shown) comprising a focusing lens and a 
self-scanning solid-state imaging device, while the displacing device 16 
is activated. More simply, the flatness of the mask 1 is detected to 
determine a deviation from the image point in a flat condition and the 
wafer 4 is deformed to conform to the deviated image point calculated 
based on reference points on the wafer 4 and the bend of the wafer 
surface. 
FIGS. 5a to 5d illustrate a principle of the operation of the substrate 
deformation correcting chuck 16. When a convex substrate 4 shown in FIG. 
5a is acted upon by a suction or vacuum from a conventional flat vacuum 
chuck 23, as shown in FIG. 5b, the top surface 11 of the substrate 4 
presents a convex shape. When the substrate 4, which can take any shape in 
accordance with the thickness of the substrate, is sucked by a chuck 24, 
as shown in FIG. 5c, the top surface 11 of the substrate 4 is made flat. A 
force for deforming the substrate 4 in the present example is the 
atmospheric pressure represented by the arrow 25 created by the vacuum 
force of the chuck 24 which pushes the substrate to the chuck 24. Other 
types of deformation forces may include an electrostatic force, an 
adherence force, a force due to contact a the top surface 11 of the 
substrate 4 or a force applied to a periphery of the substrate 4. The 
deformation of the substrate 4 is determined by an elastic deformation 
coefficient of the substrate 4 and a deformation curve of the substrate 4 
which depends on the deformation force. When the deformation force is 
small, as represented by the arrow 26 in FIG. 5d, the deformation may not 
conform to the chuck 24. A certain substrate 4 such as a wafer usually 
presents the deformation of approximately 10 .mu.m and the shape thereof 
can be approximated by a square curve within .+-.2 .mu.m error. Therefore, 
the deformation by atmospheric pressure 25 can be used. 
FIGS. 6a and 6b show an embodiment in which the substrate deformation check 
is deformed by vertically moving segments thereof so that a convex 
substrate is deformed to a flat shape. Displacing devices 36 each 
comprising a motor 33, a gear 34 and a block 35 coupled to a lead screw as 
shown in FIG. 6b are provided one set for each of the segments of the 
substrate shown in FIG. 6a. Each segment has the independent displacing 
devices 36, gap detectors 37 associated with the displacing device 36, a 
chuck body 38 including the displacing devices 36 therein for chucking the 
substrate 4, a pipe 81 for evacuating the chuck body 38 through a vacuum 
pipe (not shown), a controller 39 for processing the outputs of the gap 
detectors 37 to determine the amount of vertical movement of the 
displacing device 36, and a driver 40 for driving the motors 33. 
The substrate 4 is vacuum-drawn to follow the shape of the displacing 
devices 36. The surface 11 of the substrate 4 is moved upward or downward 
by the respective displacing devices 36. After the flatness of the top 
surface 11 of the substrate 4 has been detected, the motors 33 are driven 
in dependence upon the correction amounts and the rotational speed of the 
motors 33 are reduced by the reduction gears 34 which drive the lead 
screws which, in turn, move the blocks 35 upward or downward. When the 
motors 33 are D.C. motors, a reduction gear ratio of one to 10,000-100,000 
is needed. When they are pulse motors, they have to control the blocks 35 
by approximately 0.5 .mu.m step and they do not need large reduction gear 
ratio. The D.C. motors can be readily controlled by closed loops including 
the detectors 37, while the pulse motors can be controlled by open loops. 
The pulse motors are larger than the D.C. motors and generate heat even in 
stopped condition. For both types of motors, backlash or play needs to be 
eliminated or minimized to a controllable amount. 
The top surface of the substrate deformation correction chuck is defined by 
a plurality of the blocks 35 each of which is independently vertically 
displaceable by a small amount by the displacing device 36. The chuck body 
38 has a flange of circular, rectangular or other similar shape at a 
periphery thereof, and the substrate 4 is mounted on the flange and the 
blocks 35. The vacuum pipe 81 and the tube are connected to the chuck body 
38 and the tube is connected to the vacuum source (not shown). 
While the substrate 4 is drawn downward by the vacuum, the blocks 35 are 
driven upward or downward by small amounts by a feed back to the 
displacing devices 36 of the flatness signals detected as respective 
points of the substrate 4 corresponding to the block positions by the 
deformation measuring devices 17, so that the substrate surface is 
flattened even when the substrate surface includes unevenness, warp or 
bend or the existence of foreign materials between the substrate 4 and the 
blocks 35. 
The displacing device 36 may be the screw coupled to the motor as described 
above, or it may be a fine displacing mechanism using electrostrictive 
element, magneto-strictive element, thermal deformation element, magnets, 
fluidic devices or levers, or any combination thereof. When the substrate 
4 is a wafer, a stroke of 30 .mu.m and a positioning accuracy of no more 
than .+-.1 .mu.m are required and a deformation rate must be higher in 
terms of a throughput and be stable at the time of printing. 
The measurement of the deformation of the substrate 4 may be made by 
serially measuring a plurality of points by a single measuring element or 
by a parallel measuring of those points by a plurality of measuring 
elements. 
In any case, it is essential to measure the flatness at each point on the 
surface of the substrate 4 corresponding to each of the positions of the 
blocks 35 by any of the above measuring devices and the measuring methods. 
The light exposure device, mounted at the light exposure station B, may be 
a contact type light exposure device which exposes light with the 
photomask and the substrate being in contact, or another type light 
exposure device which exposes a pattern by irradiating ultra-violet ray, 
and for ultra-violet ray or X-ray, the photomask and the substrate are 
spaced from each other by several microns to several tens microns. Another 
light exposure device which may be used in a projection type light 
exposure device shown in FIG. 8, wherein light emitted from an exposure 
light source 50 is converted to ultra-violet ray or far ultra-violet ray 
by a filter 51, which ray is collimated by a collimator lens 52 and then 
irradiated to a photomask 1 so that a pattern 2 of a semiconductor IC or 
the like on the photomask 1 is imaged on the substrate 4 as a pattern 5 
through a projection optical system 21a comprising plane mirrors M.sub.5 
and M.sub.4, a concave mirror M.sub.1, a convex mirror M.sub.2 and a plane 
mirror M.sub.3. In this manner, the pattern is exposed to the substrate 4. 
As shown in FIGS. 7a to 7f, the shape of the blocks may be grid segments 
41, radial segments 42, concentric segments 43, multi-concentric segments 
44, parallel segments 45 or concentric and radial segments 46. 
As shown in FIGS. 9a and 9b, a thin film 56d to be described more fully 
hereinbelow, and similar to the film in FIGS. 10 and 11, may be applied 
over the displacing devices 36. The displacing device 36 may comprise a 
member 36a bonded to the bottom surface of the thin film 56d, a U-shaped 
member 36c which is clamped to the chuck body 38 and level-ajustable by a 
screw 36b, a member 36d clamped to the member 36c, a piezoelectric element 
36e having its lower end fixed to the member 36d, a ball 36f disposed 
between the upper end of the piezoelectric element 36e and the lower end 
of the member 36a and a spring 36g for tensioning the member 36a and the 
member 36d. A sphere 38a is mounted on the bottom surface of the chuck 
body 38. A stage 56s which supports the sphere 38a of the chuck body 38 by 
a spherical seat 56u is movable upward and downward by a lead screw 
mechanism, not shown. Since the substrate 4 is deformed through the thin 
film 56d while the substrate 4 is acted upon by suction and held by the 
thin film 56d, no localized stress is applied to the substrate 4 and the 
breaking of the substrate is prevented and the exposure surface of the 
substrate 4 can be smoothly deformed to conform to a desired shape. 
As an alternative to the displacing device 36, vacuum pressures to a 
plurality of chambers may be so as to deform the thin film 56d in the 
shape of diaphragm. Bore 56g are provided for enabling the substrate 4 to 
be drawn to the thin film 56d. 
The substrate deformation measuring device 17 may be of contact type or 
non-contact type. The contact type includes a dial gauge device and the 
non-contact type includes an air micrometer, electromagnetic device, 
static capacitance device, and optical device. 
Referring to FIGS. 10 and 11, preferred embodiments of the deformation 
measuring device 57(17), the substrate deformation correcting chuck 56(16) 
and the controller 58(17) are explained. The substrate deformation 
correcting chuck 56 is made of a thin, flexible metal plate such as steel, 
aluminum, stainless steel, phosphor bronze or silicon, having a thickness 
of 0.4-3 mm, a thin glass plate having a thickness of approximately 0.7 
mm, or a thin resin plate such as Teflon. It has a ring-shaped ribs 56e of 
approximately 50-100 .mu.m height around an outer periphery thereof and 
regularly arranged within the outer periphery. A chuck body 56a, having a 
flexible wafer chuck surface 56d integrally fixed to the upper end of a 
cylinder 56b, is mounted inside the rib 56e. The rib 56e may be of square 
shape or circular shape. In order to support the periphery of the wafer 
chuck surface 56d substantially freely, a ring-shaped groove 56z is formed 
to reduce the thickness. In order to eject the exposed wafer 4 by an air 
jet force, an obliquely oriented transport hole 56y is formed in the 
flexible wafer chuck surface 56d, with the hole 56y is connected to a path 
56x formed in the chuck body 56a. The path 56x is connected to a vacuum 
source 56v through a flexible pipe 56w. A shaft 56c, having a suction hole 
56f therein, is integrally fixed to the lower end of the wafer chuck 
surface 56d in the center area thereof. An opening 56g connected to the 
suction hole 56f of the shaft 56c is formed at the center of the chuck 
surface 56d and connected to a groove formed around the rib 56e. The 
suction hole 56f is connected to a vacuum source 56h through a flexible 
pipe 56i. 
The wafer deforming device includes a displacing unit 56j and an air supply 
source 56q. The displacing unit 56j comprises a block 56k in the chuck 
body 56a, a cylinder chamber 56l formed in the block 56k, ports 56m and 
56n which extend from the top and the bottom of the cylinder chamber 56l 
to the external of the chuck body 56a through the block 56k, and a piston 
56p integrally mounted to the shaft 56c and inserted in the cylinder 
chamber 56l. Connected to the air supply source 56q is a pipe 56r toward 
the displacing unit 56j. The pipe 56r includes a pressure control valve 
58b which forms the control means 58, and a direction selection valve 58a. 
The ports 56m and 56n connected to the cylinder chamber 56l are 
independently connected to output ports of the direction selection valve 
58a. The air pressure supplied from the air supply source 56q is adjusted 
by the pressure control valve 58b and fed to the port 56m or 56n selected 
by the direction selection valve 58a so that the piston 56p is moved 
upward or downward to move the shaft 56c upward or downward. As a result, 
a load is applied to the center of the thin flexible plate (chuck surface) 
56d having its periphery fixed, to create deformation w given by a formula 
(1) so that the surface of the wafer 4 is flattened in accordance with the 
following relationship. 
##EQU1## 
where: P is a load applied to the center of the thin plate 56d, 
D=Eh.sup.2 /12(1-.nu..sup.2), 
h=thickness of the plate, 
E=longitudinal elastic coefficient, 
.nu.=Poisson's ratio, 
a=fixed radius of the thin plate, 
r=variable radius of the thin plate 56d 
As shown in FIG. 10, motor 59b is driven by an instruction from a motor 
drive circuit 59a, and a lead screw mechanism (not shown) coupled to an 
output shaft of the motor 59b moves the stage 56s mounted on the carriage 
6 by a predetermined distance upward or downward as represented by an 
arrow. A spherical seat 56u is formed at the top end of the center of the 
stage 56s. The ball 56t mounted at the bottom of the chuck body 56a is 
engaged with the spherical seat 56u so that the ball may be rotated before 
it is fixed by the vacuum suction means (not shown). 
The deformation measuring device 57 comprises an air supply source 17j, a 
plate 57j fixed to the base at the substrate deformation correcting 
station, air micrometers 57a, 57b, 57c and 57d which function as 
deformation detecting elements and are arranged on the plate 57j at the 
center of the wafer 4 and peripheral positions spaced by 120 degrees from 
each other with the air micrometers 57a-57d being spaced from the surface 
of the wafer 4 which is drawn to the chuck surface 56d. Leveling pads 57k, 
57l and 57m (FIG. 11 are arranged on the plate 57j at positions 
corresponding to the positions of the air micrometers 57a, 57b, 57c and 
57d for leveling the wafer 4, with transducers 57e, 57f, 57g and 57h being 
coupled to the air micrometers 57a to 57d to transduce air pressure to 
voltage. A processing unit 57i is provided for processing the outputs of 
the transducers 57e to 57h and to provide a concave/convex signal and a 
wafer surface warp signal to the controller 58. The air supply source 17j 
supplies air of a fixed pressure to the air micrometers 57a to 57d through 
a pipe 57' and the air micrometers 57a to 57d detect air pressures which 
vary depending on distances h.sub.1 to h.sub.4 from the ends of the air 
micrometers 57a-57d to the surface of the wafer 4. The detected air 
pressures are transduced to voltages by the transducers 57e to 57h and the 
voltages are supplied to the processing unit 57i, which discriminates 
concave or convex surface based on the signals V.sub.1 -V.sub.4 from the 
transducers 57e to 57h and determines the amount of warp, and based on 
those results, controls the control means 58. 
The control means 58 of the wafer deforming means comprises the direction 
switching valve 58a, provided in the pipe 56r extending from the air 
supply source 56q to the cylinder chamber 56l of the displacing unit 56j, 
a pressure control valve 58b, provided upstream of the valve 58a, 
controllers 58c and 58d, a motor 58e, connected to the controller 58d, and 
gears 58g and 58f arranged between an output shaft of the motor 58e and a 
valve shaft of the pressure control valve 58b. The ports 56m and 56n of 
the displacing unit 56j are independently connected to output ports of the 
direction switching valve 58a through flexible pipes to selectively open 
the port 56m or 56n. Depending on the signal from the processing unit 57i 
of the deformation measuring means 57, the controller 58c controls the 
direction switching valve 58a to open the port 56m or 56n of the 
displacing unit 56j, and, depending on the signal from the processing unit 
57i, the aperture of the pressure control valve 58b is adjusted through 
the controller 58d, motor 58e, and gears 58g and 58f to control the amount 
of movement of the piston of the displacing unit 56j. 
The operation for flattening the wafer surface is now explained. The wafers 
4, housed in the magazine 19 are taken out one at a time by the transport 
mechanism 20, and coarse positioning means (not shown) mounted in the 
transport mechanism 20 pushes flat area formed on the periphery of the 
wafer 4 to coarsely position it. The coarsely positioned wafer 4 is then 
mounted on the substrate deformation correcting chuck 56 disposed at the 
wafer deformation correcting station C by the transport mechanism 20 such 
as vacuum chuck which rocks in a horizontal plane. Then, the vacuum source 
56h to the suction means is activated to draw and hold the wafer 4 to the 
chuck surface 56d. Then, the air supply source 17j of the deformation 
measuring device 57 for the wafer 4 supplies air of a fixed pressure to 
the air micrometers 57a to 57d, which detect the pressures which vary 
depending on the distances h.sub.1 to h.sub.4 from the surface of the 
wafer 4. Those pressures are transduced to the voltages V.sub.1 to V.sub.4 
by the transducers 57e to 57h. The processing unit 59c issues an 
instruction to raise the stage 56s to the motor drive circuit 59a to raise 
the stage 56s. The motor drive circuit 59a drives the motor 59b to raise 
the stage 56s by the lead screw mechanism (not shown). Thus, the areas on 
the surface of the wafer 4 sequentially abut against the leveling pads 
57k, 57l and 57m and the wafer 4 is automatically centered by the sphere 
56t and the spherical seat 56u. In this manner, the wafer 4 is leveled. 
More particularly, when the surface of the wafer 4 abuts against the 
leveling pads 57k to 57m, the transducers 57e to 57h connected to the air 
micrometers 57a to 57d produce no output variation. The processing unit 
59c detects this output state to stop the motor 59b through the motor 
drive circuit 59a which, in turn, results in a stopping in the raising of 
the stage 56s. In this manner, the wafer 4 is leveled. After the leveling 
of the wafer 4, the sphere 56t and the spherical seat 56u are fixed by air 
suction force. 
The correction of the deformation of the wafer surface is now explained. 
When the surface of the wafer 4 is not flat as shown by a phantom line in 
FIG. 10, the air micrometers 57a to 57d detect different distances h.sub.1 
to h.sub.4 between the ends of the air micrometers 57a to 57d and the 
surface of the wafer 4. The pressure transducers 57e to 57h produce the 
voltages V.sub.1 to V.sub.4 corresponding to the distances h.sub.1 to 
h.sub.4. 
The shape of the wafer 4 is determined in the following manner. The 
processing unit 57i calculates 
##EQU2## 
based on the voltages V.sub.1, V.sub.2, V.sub.3 and V.sub.4, and if 
V.sub.c .gtoreq.1, the processing unit 57i determines that the shape of 
the wafer is convex upward, and if V.sub.c &lt;1 it determines that the shape 
thereof is concave downward. The wafer 4 is formed by slicing a block into 
a thin wafer by a dicing saw, lapping the surface of the wafer and etching 
off the surface layer of the lapped wafer. Since the surface of the wafer 
4 is lapped and etched, the periphery of the wafer 4 is usually more 
treated than the center area thereof so that the surface of the wafer 4 
presents the convex shape as shown by phantom line in FIG. 10. 
Consequently, the processing unit 57i produces a signal representing 
V.sub.c &gt;1, which causes the controller 58c to actuate the direction 
switching valve 58a so that the port 56m which leads to the top of the 
cylinder chamber 58l of the displacing unit 56j is opened. 
The processing unit 57i carries out the following control and processing 
operation. If it is desired to keep the flatness of the surface of the 
wafer 4 within 3 .mu.m, for example, a reference voltage V.sub.D 
corresponding to the premeasured distances between the ends of the 
leveling pads 57k, 57l and 57m and the ends of the air micrometers 57a to 
57d, and an allowable deformation voltage V.sub..mu. corresponding to 3 
.mu.m are applied to the processing unit 57i, which calculates 
##EQU3## 
(where K is a weighting factor, e.g. 3) and determines if -V.sub..mu. 
&lt;V.sub.b -V.sub.1 &lt;V.sub..mu.,-V.sub..mu. &lt;V.sub.D -V.sub.2 
&lt;V.sub..mu.,-V.sub..mu. &lt;V.sub.D -V.sub.3 &lt;V.sub..mu. or -V.sub..mu. 
&lt;V.sub.D -V.sub.4 &lt;V.sub..mu.. The air supply source 56q is then activated 
to supply air to the upper port of the cylinder chamber 56l through the 
port 56m so that the piston 56p is moved downward through the shaft 56c. 
The processing unit 57i supplies the signal V to the controller 58d of the 
control means 58 so that the opening of the pressure control valve 58b is 
sequentially adjusted by the motor 58e and the gears 58f and 58g. When the 
conditions of -V.sub..mu. &lt;V.sub.D -V.sub.1 &lt;V.sub..mu., -V.sub..mu. 
&lt;V.sub.D -V.sub. 2 &lt;V.sub..mu., -V.sub..mu. &lt;V.sub.D -V.sub.3 &lt;V.sub..mu. 
and -V.sub..mu. &lt;V.sub.D -V.sub.4 &lt;V.sub..mu. are met, the adjustment of 
the pressure control valve 58b is stopped, the chuck surface 56d is 
deformed to present a concave shape, and the surface of the wafer 4 is 
flattened as shown by a solid line in FIG. 10. When the wafer 4 presents a 
concave shape as opposed to the previous case, the surface of the wafer 4 
can be flattened similarly. While the illustrated embodiment includes one 
shaft 56c and one piston 56j, more than one shaft 56c and piston 56j may 
be provided. In this case, the wafer 4 can be deformed to conform to the 
image surface of the mask pattern or uniformly spaced from the mask with 
high accuracy even when the surface of the wafer 4 is twisted. 
Referring to FIG. 12, another embodiment of the substrate deformation 
correcting chuck 16 is explained. The substrate deformation correcting 
chuck shown in FIG. 12 is characterized by dispensing with the obliquely 
oriented transport hole 56y for ejecting the wafer 4 in the embodiment 
shown in FIG. 10 and by connecting a controller 61 which controls the 
pressure of a deforming air chamber 60 formed on a back side of the wafer 
chuck surface 56d to the controller 58. That is, the pressure P.sub.R 
(FIG. 13a) of the deforming air chamber 60 which is controlled by the 
controller 61 and a pressure P.sub.S (FIG. 13b) due to the vertical 
movement of the shaft 56c, controlled by the direction switching valve 
58a, pressure control valve 58b, motor 58e, and gears 58f, 58g, are used 
in combination. The resiliently deformable surface of the chuck surface 
56d deforms, as shown by W.sub.R in FIG. 13a, when only the pressure 
P.sub.R of the deforming air chamber 60 is applied, and it deforms, as 
shown by W.sub.S in FIG. 13b, when only the pressure P.sub.s due to the 
vertical movement of the shaft 56c is applied. By applying both pressures, 
the chuck surface 56d deforms as shown by W in FIG. 13c, which is 
represented by the following relationship; 
EQU W=W.sub.R +W.sub.S (2) 
The deformation may be the one intermediate those shown in FIG. 13c. The 
deformation W may be expressed by: 
EQU W=W.sub.V -W.sub.F (3) 
where W.sub.F is the deformation of the top surface of the wafer on the 
flat chuck, and W.sub.V is the deformation of the top surface of the wafer 
on the chuck. Then, a condition 
EQU W.ltoreq.d (4) 
is to be met, where d is an allowable flatness. From the formulas (2), (3) 
and (4), an optimum deformation of the chuck surface 56d is determined. 
The deformation measuring device 57 performs the above calculation and the 
controller 58 feeds back the results to flatten the wafer 4. In this 
manner, even a generally convex and centrally concave wafer 4 can be 
flattened. 
Another embodiment of the substrate deformation correcting device is 
explained with reference to FIGS. 14, 15 and 16 and, according to these 
figures a chuck magazine 71 is adapted to accommodate a plurality of 
exchangeable chucks 70a to 70c as shown in FIGS. 16a-16c. A chuck 
transport means is provided for transporting the chuck 70a-70c, with the 
chuck transport means including a chuck handling mechanism generally 
designated by the reference numeral 73, motors 74a and 74b, and a 
controller 79, controlling the for transporting the exchangeable chucks 
70a to 70c from the chuck magazine 71 to a chuck base 72 (FIG. 15) and 
transporting them back to the original locations after they have been 
used. A magazine 19 is provided for accomodating unprinted wafers 4, with 
a wafer loader/unloader (transport mechanism) 20 being provided for 
mounting or dismounting a selected one of the wafer 4 on or from the 
magazine 19. A carriage 6 carries the mask and the wafer 4, with drive 
means 76 driving the carriage 6. A deformation measuring device 17(57) 
measures the deformation of the wafer 4 on the chuck by a plurality of 
aligned air micrometers or static capacitance detectors, with a chuck 
selection circuit 78 determining the shape of the wafer 4 based on the 
measurements by the deformation measuring device 17(57) to select an 
exchange chuck 70a-70c which has a shape substantially complementary to 
the shape of the wafer 4. A control unit 79 controls the chuck transport 
means based on the signal from the chuck selection circuit 78. 
More particularly, the exchangeable chucks 70a to 70c include the chuck 70c 
having a flat top surface and the chucks 70a and 70b having upwardly 
concave top surfaces of different radii of curvature, all of which are of 
stepped cylindrical shape. The chuck magazine 71 has a plurality of chuck 
accommodating grooves 71a, one for each of the exchangeable chucks 
70a-70c, opened toward the chuck handling mechanism 73. The width of the 
chuck accommodating grooves 71a is selected so as to allow slidable 
movement of a reduced diameter portion of the exchangeable chucks 70a-70c. 
The chuck handling mechanism 23 comprises a pair of arms 73a for 
releasably holding the exchangeable chuck 70a, 70b or 70c, a first support 
member 73b for pivotably supporting the arms 73a within a substantially 
right angle as shown by an arrow F, a second support member 73c for 
detachably supporting the exchangeable chuck 70a, 70b or 70c along the 
chuck accommodating groove 71a, and a motor 74b for reciprocably moving 
the second support member 73c in the direction of the arrow H, that is, in 
the direction of arrangement of the exchangeable chucks 70a to 70c. The 
carriage 6, having the chuck base 72 mounted thereon is driven by the 
drive source 75 in the direction of the arrow I, that is, in parallel to 
the direction the arrow G. The top of the chuck base 72 has a 
complementary shape to the stepped portion of the exchangeable chuck 70a, 
70b or 70c so that it closely abuts against the chuck 70a, 70b or 70c. As 
shown in FIG. 15, suction acts upon the wafer 4 through an air hole formed 
in the chuck base 72 and an air hole formed in the exchangeable chuck 70a, 
70b or 70c. The deformation measuring device 17(57) detects the level of 
the surface of the wafer 4 in synchronism with the movement of the 
carriage 6. The chuck selection circuit 78 performs the calculation to be 
described later based on the detected signal and provides an exchangeable 
chuck selection signal, optimum to the particular wafer, 4 to the chuck 
transport means. 
The function of the wafer chuck device of the present invention will now 
explained. 
The chuck magazine 71 selects one of the chucks 70a to 70c and mounts the 
selected chuck on the chuck base 72 attached to the carriage 6. This 
operation is carried out by the selection means and the transport means by 
depressing a control button (not shown). The wafer 4 is taken out from the 
magazine 19 and mounted on the chuck base 72. The wafer 4 is then acted 
upon by a suction supplied by the vacuum source. The carriage 6 is moved 
to position the wafer 4 directly beneath the substrate deformation 
measuring device 17(57) and the stage 56s (FIG. 15), supporting the chuck 
base 72, is raised to bring the top surface of the wafer 4 into contact 
with the bottoms of the leveling pads 57k to 57m. Rotational movement is 
imparted between the sphere 72a at the bottom of the chuck base 72 and the 
spherical seat of the stage 56s to level the wafer 4. Then, the sphere 72a 
and the spherical seat of the stage 56s are fixed by the vacuum force. 
Then, the stage 56s is lowered by a predetermined distance and the wafer 4 
on the carriage 6 is scanned while controlling the drive means 76. The 
deformation measuring device 17(57) detects the deformation over the 
entire wafer surface in synchronism with the movement of the carriage 6. 
The resulting data for the upwardly convex shape, for example, as shown in 
FIG. 17a, is expressed by the relationship W.sub..phi. (x, y) and is 
recorded for each crosspoint on a grid 90 shown in FIG. 18 in which the 
direction of scan of the carriage 6 is represented by x, and the direction 
normal to the direction of scan is represented by y. Based on the data 
C.sub.1 (x, y) and C.sub.2 (x, y) of the flatness of the surface of the 
exchangeable chucks 70b (FIG. 17b) and 70a (FIG. 17a), the chuck selection 
circuit 78 calculates the flatnesses of the wafers 4b and 4a when they are 
drawn to the chucks 70b and 70a, respectively, by the following formulas: 
EQU W.sub.f1 (x, y)=W.sub..phi. (x, y)+C.sub.1 (x, y) 
EQU W.sub.f2 (x, y)=W.sub..phi. (x, y)+C.sub.2 (x, y) 
From the W.sub.f1 and W.sub.f2, an area S.sub.F, which lies in a depth of 
focus (W.sub.F1 -W.sub.F2), is calculated by the following formula: 
EQU S.sub.F =.vertline.x.sub.i, y.sub.i .vertline. for .vertline.(x.sub.i, 
y.sub.i).vertline.W.sub.F1 .ltoreq.W.sub.f (x.sub.i, 
y.sub.i).ltoreq.W.sub.F2 
W.sub.f1, Wf.sub.2 and W.sub..phi. are placed in the above formula to 
select the exchangeable chuck 70a, 70b or 70c having the largest S.sub.F. 
If the flat chuck 70a, 70b, 70c has the largest S.sub.F, the wafer 4 drawn 
to the flat chuck is exposed and printed by the light exposure unit (not 
shown). The exposed and printed wafer 4 is removed from the flat chuck 
70a, 70b or 70c by means (not shown). 
As explained hereinabove, in accordance with the present invention, the LSI 
wafer having been subjected to various heat treatments and having warp or 
twist on the order of 100 .mu.m, which was heretofore comformed to the 
image surface of the mask pattern to the closeness of 15-20 .mu.m by the 
conventional process such as lapping or etching, can be deformed to 
conform to the image surface of the mask pattern within the accuracy of 
.+-.3 .mu.m by the simple structure and process without sacrificing the 
output of processed wafers. As a result, a fine pattern on the order of 
1-2 .mu.m can be formed uniformly over the entire surface of the wafer and 
the yield of the LSI and the magnetic bubble device can be considerably 
improved.