Process for projection exposure of a workpiece with back alignment marks

A process for projection exposure in which, using alignment marks on the back of a workpiece, positioning of the mask to the workpiece is performed, and a device for executing the process is achieved by the fact that exposure light is emitted from an exposure light irradiation device without the workpiece being in place. Images of alignment marks of the mask are imaged on image sensors of alignment units, and by an image processing part positions thereof are determined. According to the invention, then, a workpiece is placed on a workpiece carrier, light is emitted from alignment light irradiation devices and positions of the alignment marks of the workpiece are determined. Furthermore, the workpiece carrier is moved by the carrier drive device such that the alignment marks of the mask and workpiece come to rest on top of one another, and thus positioning of the mask to the workpiece is done. Then the exposure surface of the workpiece and the imaging position of the mask are brought into agreement with one another, exposure light is emitted from the exposure light irradiation device, and the workpiece is exposed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a projection exposure device which is used, for 
example, for production of a semiconductor device, a printed board, an LCD 
(liquid crystal display), and for similar purposes. The invention relates 
more specifically to a process for exposure in which positioning of 
alignment marks which are located on the back of a workpiece is performed 
relative to alignment marks of a mask, and in which projection exposure of 
a mask pattern onto the workpiece is produced. The invention also relates 
to a device for executing such a process. 
2. Description of Related Art 
In the production of a power transistor, micro machine, printed circuit 
board and the like, it is important to expose the pattern of a mask 
exactly in a predetermined position of a workpiece, such as a silicon 
wafer, epoxy resin and the like. The above described positioning is 
conventionally performed in such a way that the alignment marks of the 
mask and workpiece come to rest on top of one another. In particular, in a 
certain production process, there are cases in which the pattern is burned 
onto both sides of a workpiece, exact positioning of one pattern on the 
front side relative to the other pattern on the back being important. 
This means that, in the formation of the back pattern, by turning over the 
workpiece with the pattern formed on its front and then exposing the back, 
it is necessary that alignment marks which are recorded on the front 
surface, on which the pattern is already formed and which are positioned 
by turning to the back relative to the surface exposed to the mask 
alignment marks, and that the pattern on the back be positioned relative 
to the pattern of the front. (In the following, this alignment is called 
back alignment). 
In a process of manufacturing a micro machine, there is a need for accuracy 
of the above described positioning equal, for example, to roughly 1 
micron. 
The above described back alignment is conventionally used only for a 
proximity printing system in which the mask and the workpiece are caused 
to approach one another and exposure is produced. It is not used in a 
projection exposure system in which the mask pattern is projected onto the 
workpiece via a projection lens and exposure is performed. 
The projection exposure system was conventionally used for working in the 
micro domain, such as formation of chips on a wafer surface, as in a 
reduction projection exposure device of the stepper type. 
On the other hand, recently, exposure of both sides of the workpiece has 
been performed more and more often, as in a process of manufacture of a 
micro machine and the like. In this case, a double-side type of exposure 
is used more and more frequently in which, for example, one surface of the 
workpiece is subjected to precision processing by exposure by means of a 
stepper or the like, in which, then, the workpiece is turned, alignment of 
the second surface is performed using the alignment marks on the back 
surface and then exposure is performed. 
To date, the proximity printing system as was described above was 
conventional as the exposure system for double-sided exposure by executing 
back alignment. In the proximity printing system, however, it was 
considered to be a disadvantage that impurities or the like which are 
formed on the workpiece and the mask cause faults, in this case, because 
the mask and the workpiece are caused to approach one another and exposure 
is done. 
SUMMARY OF THE INVENTION 
The invention was made with consideration of the above described 
disadvantages of the prior art. 
Therefore, a first object of the invention is to devise a process for 
exposure in which, using alignment marks on the back of a workpiece and 
alignment marks of a mask, positioning of the mask relative to the 
workpiece is performed, and in which projection exposure of a mask pattern 
onto the workpiece can be produced, and a device for executing the 
process. 
A second object of the invention is to devise a process for projection 
exposure in which automatic positioning of the alignment marks on the back 
of a workpiece relative to the alignment marks of a mask is performed, and 
in which projection exposure of a mask pattern onto the workpiece can be 
achieved, and a device for executing the process. 
The above described objects are achieved according to the invention by the 
fact that, in a projection exposure device which has an exposure light 
irradiation device for emitting exposure light, a mask on which a mask 
pattern and alignment marks are recorded, a projection lens, a workpiece, 
on the back of one exposure surface of which alignment marks are recorded, 
and alignment determination systems for determining the positions of the 
above described alignment marks of the mask and the workpiece and for 
positioning of the two to one another, positioning of the mask to the 
workpiece is done in the manner described below in (1) to (5), and that 
projection exposure of the mask pattern onto the exposure surface of the 
workpiece is achieved. 
The objects are achieved according to the invention furthermore by the 
projection exposure device being arranged in the manner described below in 
(6) and (7), by back alignment being performed, and by projection exposure 
of the mask pattern on the exposure surface of the workpiece being 
produced. 
(1) Process for projection exposure according to solution 1 according to 
the invention: 
(a) The positions of the alignment marks of the mask are determined in the 
state in which the workpiece is not yet present, and in which the imaging 
positions of the mask pattern and the alignment marks agree with the focal 
positions of the alignment determination systems. 
(b) The positions of the alignment marks of the workpiece are determined in 
a state in which the workpiece is in place, and in which the alignment 
marks of the workpiece agree with the focal positions of the alignment 
determination systems. 
(c) Positioning of the alignment marks of the mask relative to the 
alignment marks of the workpiece is produced. 
(d) The exposure surface of the workpiece is brought into agreement with 
the imaging positions of the mask pattern and the alignment marks. The 
mask pattern is projected onto the workpiece from the exposure light 
irradiation device via the mask and the projection lens, and the workpiece 
is exposed. 
(2) Process for projection exposure according to solution 2 according to 
the invention 
(a) Imaging positions of the mask pattern and the alignment marks are 
brought into agreement with the focal positions of the alignment 
determination systems, the workpiece not yet being present. Projection 
images of the alignment marks of the mask which are located in the above 
described imaging positions are picked up and subjected to image 
processing. Thus the positions of the alignment marks of the mask are 
determined and/or stored. 
(b) The workpiece is placed and moved in a direction perpendicular to its 
exposure surface. The alignment marks of the workpiece are brought into 
agreement with the focal positions of the alignment determination systems. 
The positions of the alignment marks of the workpiece are determined 
and/or the images of the alignment marks are displayed. 
(c) The workpiece is moved such that the alignment marks of the mask and 
the workpiece come to rest on top of one another. 
(d) The exposure surface of the workpiece and the imaging position of the 
mask are brought into agreement with one another. The mask pattern is 
projected onto the workpiece from the exposure light irradiation device 
via the mask and the projection lens, and the workpiece is exposed. 
(3) Process for projection exposure according to solution 3 according to 
the invention 
(a) The imaging positions of the mask pattern and the alignment marks are 
brought into agreement with the focal positions of the alignment 
determination systems, the workpiece not yet being present. Projection 
images of the alignment marks of the mask are picked up and subjected to 
image processing. Thus, the positions of the alignment marks of the mask 
are determined and/or stored. 
(b) The workpiece is placed. The alignment determination systems are moved 
in the direction perpendicular to the workpiece exposure surface. The 
surface of the workpiece on which the alignment marks are recorded is 
brought into agreement with the focal positions of the alignment 
determination systems. The positions of the alignment marks of the 
workpiece are recorded and subjected to image processing. The positions of 
the alignment marks of the workpiece are determined and/or images of the 
alignment marks are displayed. 
(c) The workpiece is moved such that the alignment marks of the mask and 
the workpiece come to rest on top of one another. 
(d) The exposure surface of the workpiece and the imaging position of the 
mask are brought into agreement with one another. The mask pattern is 
projected onto the workpiece from the exposure light irradiation device 
via the mask and the projection lens, and the workpiece is exposed. 
(4) Process for projection exposure according to solution 4 according to 
the invention 
(a) The imaging positions of the mask pattern and the alignment marks, 
focal positions of the alignment determination systems and one surface of 
a workpiece carrier on which the workpiece is placed are brought into 
agreement with one another in the state in which the workpiece is not yet 
present. The projected images of the alignment marks of the mask are 
picked up and are subjected to image processing. Thus, the positions of 
the alignment marks of the mask are determined and/or stored. 
(b) The workpiece is placed on the workpiece carrier. The positions of the 
alignment marks of the workpiece are picked up and subjected to image 
processing. The positions of the alignment marks of the workpiece are 
determined and/or the images of the alignment marks are displayed. 
(c) The workpiece is moved such that the alignment marks of the mask and 
the workpiece come to rest on top of one another. 
(d) The mask and/or the projection lens is/are moved in a direction 
perpendicular to the workpiece exposure surface. The exposure surface of 
the workpiece and the imaging position of the mask are brought into 
agreement with one another. The mask pattern is projected onto the 
workpiece from the exposure light irradiation device via the mask and the 
projection lens, and the workpiece is exposed. 
(5) Process for projection exposure according to solution 5 according to 
the invention 
(a) The exposure surface of the workpiece is brought into agreement with 
the imaging position of the mask pattern and the alignment marks with one 
another. One surface of the workpiece on which the alignment marks are 
recorded, and the focal positions of the alignment determination systems 
are brought into agreement with one another. In the state in which the 
workpiece is not yet present, in the optical path between the projection 
lens and imaging positions of the projection images of the mask pattern 
and the alignment marks, position correction plates are inserted which 
move the imaging positions of the mask pattern and the alignment marks 
from their actual imaging positions by a length which corresponds to the 
thickness of the workpiece to be exposed. The projection images of the 
mask alignment marks are picked up and subjected to image processing. 
Thus, the positions of the alignment marks of the mask are determined 
and/or stored. 
(b) The workpiece is placed. The positions of the alignment marks of the 
workpiece are picked up and subjected to image processing. The positions 
of the alignment marks of the workpiece are determined and/or the images 
of the alignment marks are displayed. 
(c) The workpiece is moved such that the alignment marks of the mask and 
the workpiece come to rest on top of one another. 
(d) The mask pattern is projected onto the workpiece from the exposure 
light irradiation device via the mask and the projection lens, and the 
workpiece is exposed. 
(6) Device for projection exposure according to solution 6 according to the 
invention 
In a projection exposure device which has an exposure light irradiation 
device for emitting exposure light onto a mask, a mask carrier on which is 
placed a mask on which a mask pattern and alignment marks are recorded, a 
projection lens for projection of images of the mask pattern and of the 
alignment marks which are recorded on the mask, and a workpiece carrier on 
which a workpiece is placed, the workpiece carrier is provided with 
observation window parts for observation of alignment marks which are 
recorded on the back of the mask pattern projection surface of the 
workpiece. Furthermore, here, there are alignment determination systems 
for observing the alignment marks of the mask and workpiece opposite the 
observation window parts. The alignment determination systems determine 
the positions of the mask and workpiece alignment marks, and thus 
positioning of the mask alignment marks relative to the workpiece 
alignment marks is performed. 
(7) Device for projection exposure according to solution 7 according to the 
invention 
There are an exposure light irradiation device for emitting exposure light 
onto a mask, a mask carrier on which is placed a mask on which a mask 
pattern and alignment marks are recorded, a projection lens for projection 
of images of the mask pattern and of the alignment marks which are 
recorded on the above described mask, a workpiece carrier on which a 
workpiece is placed and which is provided with an observation window parts 
for observation of alignment marks which are recorded on the back of the 
placed workpiece, an image processing means which subjects the mask and 
workpiece alignment marks recorded via the observation window parts to 
image processing and determines/stores the positions of the two alignment 
marks, and a control means. The image processing means determines and 
stores the positions of projected images of the mask alignment marks which 
are determined in the state in which the workpiece is not placed on the 
workpiece carrier. Furthermore, the image processing means determines the 
positions of the alignment marks which are recorded on the back of the 
workpiece and which are determined in the state in which the workpiece is 
placed on the workpiece carrier. The above described control means moves 
the workpiece carrier parallel to the exposure surface of the workpiece, 
such that the mask and workpiece alignment marks come to rest on top of 
one another. Thus, projection exposure of the mask pattern onto the 
workpiece is performed. 
In the invention described above using solutions 1 through 5, the mask can 
be positioned relative to the workpiece with high precision using the 
alignment marks on the back of the workpiece and the mask alignment marks 
by the measure by which positioning of the mask alignment marks relative 
to the workpiece alignment marks is performed in the manner described 
above in (1) through (5) and by which projection exposure of the mask 
pattern onto the workpiece is achieved. 
Furthermore, back alignment can be done without moving the workpiece and 
the like by the measure described above in (3) and (5), by which the 
alignment determination systems are moved in a direction perpendicular to 
the exposure surface of the workpiece, and in this way, the workpiece 
surface provided with the alignment marks is brought into agreement with 
the focal positions of the alignment determination systems, or by which 
the position correction plates are inserted and the imaging positions of 
the mask pattern and alignment marks are moved. 
In the invention described using solutions 6 through 7, by means of the 
arrangement of the projection exposure device described above for (6) and 
(7), the alignment marks on the back of the workpiece can be observed via 
the observation window parts located in the workpiece carrier, and thus, 
back alignment can be produced with high precision using a device with a 
simple mechanism. 
Furthermore, back alignment can be obtained automatically by the measure 
described above in (7), by which there are an image processing means and 
control means by which the positions of the projection images of the mask 
alignment marks are determined and stored by the image processing means, 
and furthermore, the positions of the alignment marks recorded on the back 
of the workpiece are determined, and by which the workpiece carrier is 
moved by the control means such that the mask and workpiece alignment 
marks come to rest on top of one another. 
These and further objects, features and advantages of the present invention 
will become apparent from the following description when taken in 
connection with the accompanying drawings which, for purposes of 
illustration only, show several embodiments in accordance with the present 
invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the arrangement of an exposure device which is used for 
positioning a mask relative to a workpiece according a first and a second 
embodiment of the invention according to the invention. In the figure, 
numeral 1 designates an exposure light irradiation device which emits 
exposure light, for example, an i-line, an h-line and a g-line (i-line: 
365 nm wavelength, h-line: 405 nm wavelength, g-line: 436 nm wavelength) 
onto a mask such that the illumination intensity on the surface of mask M 
becomes uniform. A pattern and alignment marks MA are recorded on mask M. 
As shown, for example in FIG. 2, the exposure light irradiation device 1 
has a high pressure mercury lamp 1a as the light source in its interior. 
Light from the high pressure mercury lamp 1a is focussed by oval focussing 
mirror 1b and is emitted via flat reflector 1c, integrator lens 1d, flat 
reflector 1e and condenser lens 1f onto mask M. 
In FIG. 1, reference number 2 designates a mask drive device which moves 
the position of mask M in the Z-direction (up and down in FIG. 1) and 
which also, for example at a preset of the mask M or the like, rotates the 
position of mask M around a straight line which is parallel to the 
exposure light axis (hereafter this rotation is called "motion in the 
.theta. direction"). Furthermore, mask drive device 2 moves the position 
of mask M in the X-Y directions (in two directions on one plane which 
orthogonally intersects the direction of the exposure light axis). 
Specifically, mask drive device 2 moves a conventional mask carrier (not 
shown) and which holds mask M securely in the above described manner, with 
which both manual control using a micrometer head and also automatic drive 
using a servomotor or the like can be utilized. 
Additionally, a projection lens 3 projects the pattern and alignment marks 
MA on mask M onto a mask pattern projection surface 4. Reference number 31 
indicates a projection drive device which moves a carrier (not shown) for 
positioning the projection lens in the Z-direction, with which both manual 
control using a micrometer head and also automatic drive using a 
servomotor or the like can be utilized. 
A workpiece carrier 5 fixes wafer W (workpiece) in position, for example, 
by suction via a vacuum suction holder (not shown). Workpiece carrier 5, 
furthermore, has an observation openings 52 for observing the alignment 
marks WA which are recorded on the back of the wafer W. A carrier drive 
device 51 is provided for moving the workpiece carrier 5 in the 
X-Y-.theta.-Z directions, with which both manual control using a 
micrometer head and also automatic drive using a servomotor or the like 
can be utilized. 
Reference number 6 indicates an alignment light irradiation device which 
irradiates alignment mark WA of the wafer W with light via a condenser 
lens 61, a half mirror 62 and an objective lens 7 through an observation 
opening 52. 
FIG. 3 is a schematic representation of one example for an arrangement of 
the alignment light irradiation devices 6 which has in its interior, a 
lamp 6a, such as a halogen lamp or the like, and a current source 6b for 
the lamp 6a. Light from lamp 6a is supplied via an infrared cut filter 6c 
and a light guide 6d composed of optical fibers to the condenser lens 61. 
The light emitted from alignment light irradiation device 6 need not have a 
limited wavelength. However, in the case in which the mask pattern is 
exposed onto the back of wafer W, it is more advantageous to have 
nonexposure light emitted which, for example, does not contain i-line, 
h-line nor g-line light, each of which have an exposure wavelength. 
In FIG. 1, reference number 8 indicates an image sensor which picks up the 
projected image of the alignment mark of mask M via the objective lens 7 
as well as half mirror 62, if wafer W is not yet present on workpiece 
carrier 5. On the other hand, in the case in which wafer W is present on 
the workpiece carrier, it picks up the projected image of the wafer 
alignment mark by alignment light irradiation device 6 via objective lens 
7 and half mirror 62. 
Alignment unit 70 is formed of the objective lens 7 and the pertinent 
optical parts, for example, alignment light irradiation device 6, 
condenser lens 61, half-mirror 62 and image sensor 8 or the like. An 
alignment unit drive device 71 has the function of moving the alignment 
units 70 in the Z-direction. 
This means that only when the objective lenses 7 move do the above 
described associated optical parts deviate from the optical paths of the 
images of the objective lenses 7, by which monitoring of the projected 
images by objective lenses 7 becomes no longer possible. The objective 
lenses 7 and the associated optical parts are, therefore, formed as units, 
as was described above, and are moved by means of alignment unit drive 
device 71. Furthermore, alignment unit drive device 71 can be subjected 
both to manual control and also automatic control, like the mask drive 
device 2. Reference number 9 indicates an image processing part which 
subjects the images of the alignment marks picked up by image sensors 8 to 
image processing. 
FIG. 4 schematically shows the arrangement of a control system for 
automatically controlling of positioning/exposure in the first and second 
embodiment. As in FIG. 1, in FIG. 4, numeral 70 indicates the alignment 
unit, 9 the image processing part which receives images of the alignment 
marks MA from the image sensors 8, numeral 2 indicates the mask drive 
device for driving mask M in the X-Y-Z-.theta. directions, 31 the 
projection lens drive device for driving projection lens 3 in the 
Z-direction, 51 a carrier drive device for driving workpiece carrier 5 on 
which wafer W is placed in the X-Y-Z-.theta. directions, and 71 the 
alignment unit drive device for driving alignment units 70. In addition, a 
monitor is indicated by 10 and a control member by 11. 
In the following, the alignment sequence in the first process embodiment of 
the invention is described with reference to the device shown in FIG. 1: 
(1) Mask M is located in a predetermined position. 
(2) Exposure light from exposure light irradiation device 1 is emitted onto 
mask M in the state in which wafer W is not yet present on workpiece 
carrier 5. The pattern and alignment marks MA of mask M are imaged by 
projection lens 3 onto the mask pattern projection surface 4. In this 
case, mask M and projection lens 3 are adjusted beforehand by means of 
mask drive device 2 and projection drive device 31, such that the mask 
pattern projection surface 4 and the surface of wafer W agree with one 
another. 
(3) Using alignment unit drive device 71, objective lenses 7 are adjusted 
in the X-direction or Y-direction, such that the images of the alignment 
marks MA of mask M extend into the visual fields of the image sensors 8. 
Then, the objective lenses 7 are adjusted in the Z-direction such that the 
images of alignment marks MA of mask M are imaged on the image sensors 8. 
If this adjustment is done once, it need not be repeated if the mask M 
remains in place. 
If the images of alignment marks MA of mask M are picked up by image 
sensors 8, the positions of alignment marks MA are determined and stored 
at image processing part 9. Often an image processing method, such as a 
"pattern search" based on pattern information recorded beforehand, feature 
extraction or the like is used for this determination. 
In the case in which positioning is done not by automatic processing, but 
is performed manually by the operator, an image freeze unit is used and 
the recorded images of alignment marks MA are temporarily retained (if 
later the images of alignment marks WA of wafer W are picked up, the 
images of alignment marks WA of wafer W are placed on top of one another 
on the above described retained images of alignment marks MA of mask M and 
displayed). 
Alternatively, a reference line is generated on the screen of the monitor 
10 using reference lines generating unit, objective lenses 7 are moved by 
alignment unit drive device 71 and the images of alignment marks MA are 
brought into agreement with the reference lines (if later, the images of 
alignment marks WA of wafer W are picked up, wafer W is moved and the 
images of alignment marks WA of wafer W are brought into agreement with 
the noted reference lines). Other similar methods can also be used for 
this purpose. Determination of the above described "freeze" image can be 
done manually by the operator, or it can be automatically processed in a 
predetermined sequence. 
(4) Irradiation of mask M with exposure light from exposure light 
irradiation device 1 is stopped. 
(5) Wafer W is placed on workpiece carrier 5. The back or the front and 
back sides of wafer W are provided with alignment marks WA beforehand. The 
term "back" here is defined as the side which is faces away from the mask 
M. The position of wafer W is preset by engaging it against a positioning 
means located on the workpiece carrier 5, for example, a positioning pin 
or the like. Alignment marks WA on the back of wafer W are, therefore, 
positioned in the vicinity of observation opening 52. 
(6) From alignment light irradiation devices 6 light is radiated which is 
emitted onto the back of wafer W through observation opening 52 of 
workpiece carrier 5. In doing so, it is more advantageous that nonexposure 
light is emitted from alignment light irradiation devices 6 which light 
contains, for example, neither i-line, h-line nor g-line light, each of 
which have an exposure wavelength, in the case in which a light-sensitive 
agent is applied to the back of wafer W. 
(7) Mask pattern projection surface 4 and image sensors 8 are at an imaging 
ratio to one another produced by objective lenses 7. Workpiece carrier 5 
is, therefore, moved by carrier drive device 51 in the Z-direction such 
that the images of alignment marks WA on the back of wafer W are imaged on 
the image sensors 8. 
In doing so, instead of moving the workpiece carrier 5 in the Z-direction, 
alignment units 70 can be driven by alignment unit drive device 71, can 
move objective lenses 7 in the Z-direction, and bring the back of wafer W 
and image sensors 8 into an imaging ratio to one another. 
The above described adjustment can be performed automatically by 
controlling the workpiece carrier drive device 71 by control member 11 
shown in FIG. 4. However, it can also be performed manually by watching 
the screen of the monitor 10. 
(8) Next, the alignment marks WA of workpiece W are picked up by the image 
sensors 8 and determined at the image processing part 9. Workpiece carrier 
5 is moved by means of the carrier drive device 51 in the X-direction, 
Y-direction or .theta.-direction, such that alignment marks MA of the mask 
and the alignment marks WA on the back of wafer W, which were determined 
and stored at the start, come to rest on top of one another. 
This positioning is done automatically, as was described above, by 
workpiece carrier drive device 51 being controlled by control member 11 
moving workpiece carrier 5 in the X-Y-.theta. directions, such that the 
positions of the alignment marks MA of the mask M stored and determined by 
the image processing part 9 agree with the positions of alignment marks WA 
of the wafer W. 
Furthermore, as was described above, the image freeze unit stores the 
images of the alignment marks MA of the mask, alignment marks WA of wafer 
W are displayed on monitor 10, the above-described retained images of the 
alignment marks MA of mask M are placed on top of one another on the 
images of the alignment marks WA of the wafer W and are displayed, and 
thus, manual positioning is achieved. Alternatively, manual positioning 
can also be performed by bringing the reference line generated by the 
reference line generating unit into agreement, beforehand, with the 
positions of the alignment marks MA of the mask M, and by alignment marks 
WA of wafer W being brought into agreement with this reference line. 
(9) In the case in which, in above described step (7), the workpiece 
carrier 5 was moved in the Z-direction, mask pattern projection surface 4 
and the back of wafer W agree. Workpiece carrier 5, therefore, is moved 
using the carrier drive device by the same amount as the amount of 
movement in step (7) but in the opposite direction. Thus, the surface of 
the wafer W and the mask pattern projection surface 4 are brought into 
agreement with one another. 
Positioning of mask M relative to wafer W and preparation for exposure are 
completed with the above described sequence. 
(10) Exposure light is emitted onto mask M from exposure light irradiation 
device 1. The mask pattern is projected onto wafer W and thus wafer W is 
exposed. 
In the case in which the above described positioning is performed, and in 
which, after completion of exposure, the next wafer W is placed and 
positioned, it is afterwards unnecessary to adjust the positions of mask 
M, projection lens 3 and objective lenses 7. Therefore, only above 
described positioning steps (5), (6), (7), (8), (9) and (10) need be done. 
But, in the case in which, as a result of changes of ambient temperature, 
the positions of mask M and projection lens 3 change, it is necessary to 
again perform above described steps (2), (3) and (4), since the positions 
of mask pattern projection surface 4 and alignment marks MA change. 
In steps (3) and (7), in this embodiment, the positions of objective lenses 
7 are adjusted using alignment unit drive device 71, such that the images 
of the alignment marks MA of mask M are imaged on the image sensors 8. 
However, an image sensor drive device for driving image sensors 8 can also 
be utilized to adjust the positions of image sensors 8, while objective 
lenses 7 remain fixed, and thus, the images of the alignment marks MA of 
the mask M can be imaged on image sensors 8. 
As was described above, in this embodiment, back alignment can be performed 
automatically with high precision by the measure in which the workpiece 
carrier 5 is provided with observation openings 52 for observing the 
alignment marks WA on the back of wafer W, in which the back of wafer W is 
aligned relative to the alignment units 70, in which the projected images 
of alignment marks MA of mask M and the alignment marks WA on the back of 
wafer W are picked up through the observation opening 52 by means of the 
alignment units 70, and in which positioning of the two relative to one 
another is achieved. 
Instead of moving wafer W in the Z-direction, in above described step (7), 
the alignment units 70 can be driven by means of alignment unit drive 
device 71, objective lenses 7 can be moved in the Z-direction and the back 
of wafer W and image sensors 8 can be brought into an imaging ratio with 
respect to one another. For this reason, a device for moving the wafer W 
in the Z-direction is no longer necessary. 
In the following, the alignment sequence in accordance with a second 
process embodiment of the invention is described with reference to the 
device shown in FIG. 1: 
In this embodiment, using mask drive device 2 and projection lens drive 
device 31, the mask pattern projection surface 4 and the back of wafer W 
are brought into agreement with one another. Otherwise, this embodiment is 
essentially identical to the first embodiment. 
(1) Mask M is located in a predetermined position. 
(2) Alignment light from alignment light irradiation device 1 is emitted 
onto mask M prior to placing of the wafer W on the workpiece carrier 5. 
The pattern and alignment marks MA of the mask M are imaged by projection 
lens 3 onto mask pattern projection surface 4. 
(3) Using mask drive device 2 and projection lens drive device 31, the mask 
M and the projection lens 3 are moved in the Z-direction. Thus, the mask 
pattern projection surface 4 and the back of wafer W are brought into 
agreement with one another. 
(4) Objective lenses 7 are adjusted in the X-direction or Y-direction and 
then in the Z-direction, such that the images of the alignment marks MA of 
the mask M are imaged on the image sensors 8. If this adjustment has been 
done once, it need then not be repeated if the mask M remains in place. 
If the images of alignment marks MA of mask M were picked up by image 
sensors 8, the positions of alignment marks MA are determined and stored 
at image processing part 9. Often, an image processing method, such as a 
"pattern search" based on pattern information recorded beforehand, feature 
extraction or the like is used for this determination. 
In the case in which positioning is performed manually by the operator 
instead of by automatic processing, an image freeze unit is used or the 
reference line generation unit is used, as was described above. 
(5) Irradiation of mask M with exposure light from exposure light 
irradiation device 1 is stopped. 
(6) Wafer W is placed on workpiece carrier 5. The back side or the front 
and back sides of wafer W having alignment marks WA which were applied 
beforehand. The term "back" here is defined as the side which faces away 
from mask M. The position of the wafer W is preset by engaging it against 
a positioning means located on workpiece carrier 5, for example, a 
positioning pin or the like. Alignment marks WA on the back of workpiece W 
are, therefore, positioned in the vicinity of observation openings 52. 
(7) Light is irradiated from alignment light irradiation devices 6 and is 
emitted onto the back of wafer W through observation openings 52 of 
workpiece carrier 5. In doing so, it is more advantageous that the light 
emitted from the alignment light irradiation devices 6 is nonexposure 
light which, for example, contains neither i-line, h-line nor g-line 
light, each of which has an exposure wavelength, in the case in which a 
light-sensitive agent is applied to the back of wafer W. 
(8) Image sensors 8 are brought to an imaging ratio with respect to each 
other and mask pattern projection surface 4, i.e., with the back of wafer 
W, by objective lenses 7. Alignment marks WA of wafer W are, therefore, 
picked up by image sensors 8 and determined at image processing part 9. 
Workpiece carrier 5 is, therefore, moved by carrier drive device 51 in the 
X-direction, Y-direction or .theta.-direction such that the alignment 
marks MA of the mask and the alignment marks WA on the back of wafer W 
which were determined and stored beforehand come to rest on top of one 
another. 
This positioning is done automatically by workpiece carrier drive device 51 
controlled by control member 11 moving workpiece carrier 5 in the 
X-Y-.theta. directions, as was described above. 
Furthermore, as was also described above, manual positioning can also be 
performed by means of the image freeze unit and the reference line 
generation unit. 
(9) Mask pattern projection surface 4 and the back of wafer W agree with 
one another. Mask M or projection lens 3 is, therefore, moved in a 
direction opposite to the direction of movement in above described step 
(3) by the same amount as the thickness of wafer W using mask drive device 
2 or projection lens drive device 31. Thus, the mask pattern projection 
surface 4 and the surface of wafer W are brought into agreement with one 
another. 
Positioning of mask M relative to wafer W and preparation for exposure are 
completed with the above described sequence. 
(10) Exposure light is emitted onto mask M from exposure light irradiation 
device 1. The mask pattern is projected onto wafer W, and thus, wafer W is 
exposed. 
In the case in which the above described positioning is performed, and in 
which, after completion of exposure, the next wafer W is placed and 
positioned, it is afterwards unnecessary to adjust the positions of 
objective lens 7. Therefore only above described positioning steps (6), 
(7), (8), and (10) need be done. 
But, in the case in which, as a result of changes of ambient temperature, 
the positions of mask M and projection lens 3 change, it is necessary to 
again perform the steps (2), (3), (4), (5) and (9) as was described above. 
As was also described above, in this embodiment, the same effects as in 
the first embodiment can be obtained by the measure by which mask M and 
projection lens 3 are moved in the Z-direction, by which the surface of 
wafer W provided with alignment marks WA and the surface on which 
alignment marks MA of mask M are imaged are brought into agreement with 
one another beforehand, by which the alignment marks MA of the mask M are 
stored, by which then wafer W is moved such that alignment marks WA of 
wafer W and the above stored positions of alignment marks MA of mask M 
come to rest on top of one another. Furthermore, it is unnecessary to 
additionally position a device for moving wafer W in the Z-direction. 
FIG. 5 is a schematic of a device for performing a third process embodiment 
of the invention. In this embodiment, using optical components, the 
workpiece surface provided with alignment marks WA and the projection 
surface of the alignment marks MA of the mask are brought into agreement 
with one another. 
In the following, the third process embodiment of the invention is 
described with reference to FIG. 5: 
In the drawing parts with the same functions as in FIG. 1 are labelled with 
the same reference numbers as in FIG. 1. Specifically, reference numeral 1 
designates the exposure light irradiation device, reference numeral 2 the 
mask drive device, 3 the projection lens, 4 the mask pattern projection 
surface, 5 the workpiece carrier and 52 the observation opening. 
Furthermore, 6 is the alignment light irradiation device, 61 a condenser 
lens, 62 the half mirror and 7 the objective lens. Alignment unit 70 is 
formed from the objective lens 7 and the associated optical parts, such 
as, for example, alignment light irradiation device 6, condenser lens 61, 
half mirror 62, image sensors 8 or the like. Alignment units 70 are driven 
by alignment unit drive device 71. Reference numeral 9 indicates the image 
processing part which subjects the alignment mark images picked up by 
image sensors 8 to image processing. 
Carrier drive device 51, in this embodiment, executes linear motion or 
rotation of the position of workpiece carrier 5 in the X-Y directions. 
However, it need not move the workpiece carrier 5 in the Z-direction, as 
in the first embodiment. 
In contrast to the FIG. 1, embodiment, an optical component L, in the form 
of a parallel flat plate. Optical components L, as shown in the drawing, 
are inserted into and removed from the optical paths in which alignment 
marks MA of mask M are imaged by projection lens 3 onto mask pattern 
projection surface 4. The insertion positions are located between 
projection lens 3 and mask pattern projection surface 4. When optical 
components L are inserted, the imaging positions of the projection images 
of alignment marks MA of the mask M on mask pattern projection surface 4 
move in the Z-direction, as is shown in FIG. 6 using the broken lines. 
As was described above, the exposure light emitted from exposure light 
irradiation device 1 travels through optical components L. Therefore, a 
glass material is desirable for this purpose which has a high transmission 
factor of light with exposure light wavelengths (for example, the i-line, 
h-line and g-line light) and which has a slight change of the transmission 
factor over time. Specifically, quartz glass, soda lime glass, crown glass 
or the like is selected as the glass material. 
Thickness d of the optical components L is computed according to the 
following formula, when the index of refraction of the glass material used 
is designated n and the thickness of the wafer (workpiece) dw: 
EQU d=dw/(1-(1/n))=(n/(n-1))dw 
A optical component position controlling device L1 controls the positions 
of the optical components, inserting the optical components L into and 
removing them from the optical paths in which the alignment marks MA of 
the mask M are imaged by projection lens 3 onto the mask pattern 
projection surface 4. For insertions, optical component position 
controlling device L1 produces linear motion and rotary motion of optical 
components L in the X-Y-Z directions. 
This means that the optical component position controlling device L1 has 
the functions both of insertion and removal of the optical components L as 
well as the function of adjustment of the insertion positions. The two 
functions are independent of one another. If, on the one hand, the 
insertion positions have been set, these insertion positions do not 
change, even if insertion and removal of optical components L are 
repeated. 
Specifically, optical component position controlling device L1, for 
example, the carriers (not shown) which fix optical components L in 
position in the above described manner. In this case, both manual control 
using a micrometer head or the like and also automatic control using a 
servomotor or the like can be performed. 
In this embodiment, the control system shown above in FIG. 4 can be used 
for automatic control of positioning/exposure. In this embodiment, an 
arrangement can be provided in which the FIG. 4 control member 11 controls 
the optical component position controlling device L1 instead of projection 
lens drive device 31. 
Next, the alignment sequence in the exposure device according to the third 
embodiment of the invention is described: 
(1) Wafer W or a reference workpiece with a back provided with alignment 
marks WA is placed on workpiece carrier 5. Light is emitted from alignment 
light irradiation devices 6. Wafer W, or the workpiece used as a 
reference, is pushed against a positioning means located on workpiece 
carrier 5, such as a positioning pin or the like, and is thus preset. 
Alignment marks WA on the back of wafer W are therefore positioned in the 
vicinity of observation openings 52. 
Light is radiated onto the back of wafer W, or the workpiece used as the 
reference, through observation openings 52 of workpiece carrier 5. In 
doing so, it is more advantageous that from nonexposure light is emitted 
from the alignment light irradiation devices 6 which light, for example, 
contains neither the i-line, g-line nor h-line, each of which have an 
exposure wavelength, in the case in which a light-sensitive agent is 
applied to the back of wafer W. 
(2) Using alignment unit drive device 71, the objective lenses 7 are 
adjusted in the X-direction or Y-direction, such that the images of the 
alignment marks WA on the back of wafer W or the reference workpiece are 
imaged on the image sensors 8, and that the images of the alignment marks 
WA extend into the visual fields of image sensors 8. Then, the objective 
lenses 7 are adjusted in the Z-direction, such that the images of the 
alignment marks WA are imaged on image sensors 8. 
The positions of objective lenses 7 are adjusted by the above described 
activation. This adjustment need only be done once. Alignment marks WA 
were used above to adjust the positions of objective lenses 7. However, 
there is no need to be limited to alignment marks WA, and other suitable 
patterns can be used which can be observed through observation openings 
52. 
(3) Emission of light from alignment light irradiation devices 6 is 
stopped. Wafer W or the reference workpiece is removed from workpiece 
carrier 5. 
(4) Irradiation of mask M with exposure light from exposure light 
irradiation device 1 is started. 
(5) Optical components L are inserted into the space between projection 
lens 3 and mask pattern projection surface 4 by optical component position 
controlling device L1. Optical parts L, as shown in FIG. 6, move the 
imaging positions of alignment marks MA of mask M on mask pattern 
projection surface 4 in the Z-direction when they are inserted. 
(6) The insertion positions of optical components L are set by optical 
component position controlling device L1. When optical components L are 
inserted, they must unconditionally be inserted in the optical paths of 
the projection images of alignment marks MA of the mask M. 
This adjustment need no longer be done afterwards if the positions of 
alignment marks MA do not change. 
By inserting optical components L, the images of the alignment marks MA of 
mask M are projected in the vicinity of the positions in which alignment 
marks WA on the back of wafer W or the reference workpiece in above 
described step (2) were present. They are, therefore, imaged via objective 
lenses 7 and half mirrors 62 in image sensors 8. 
(7) If, by means of image sensors 8, the images of the alignment marks MA 
of mask M were picked up, the positions of the alignment marks MA are 
determined and stored at image processing part 9. 
Often, an image processing method, such as a "pattern search" based on 
pattern information recorded beforehand, feature extraction or the like is 
used for this determination. 
In the case in which positioning is performed manually by the operator 
instead of by automatic processing, an image freeze unit can be used or a 
reference line generating unit can be used, as was described above. 
(8) Irradiation of light onto mask M from exposure light irradiation device 
1 is stopped. 
(9) Optical components L are removed from the space between the projection 
lens 3 and the mask pattern projection surface 4 by the optical component 
position controlling device L1. In the case in which optical components L 
do not screen the optical path of the projected images of the mask 
pattern, it is not necessary to remove them from the above described 
space. 
(10) Wafer W, as the workpiece to be exposed, is placed in a predetermined 
position on workpiece carrier 5. For example, wafer W is pushed against a 
positioning means, such as a positioning pin or the like, located on 
workpiece carrier 5, and is thus preset. Alignment marks WA on the back of 
wafer W are, therefore, positioned in the vicinity of the observation 
openings 52. 
(11) Light is radiated from alignment light irradiation devices 6. The 
light is radiated onto the back of the wafer W through the observation 
openings 52 of the workpiece carrier 5. In doing so, it is more 
advantageous that nonexposure light is emitted from alignment light 
irradiation devices 6 which, for example, does not contain the i-line, 
h-line nor g-line light, each of which have an exposure wavelength, in the 
case in which a light-sensitive agent is applied to the back of wafer W. 
(12) Alignment marks WA of wafer W which are determined at image processing 
part 9 are picked up by image sensors 8. Workpiece carrier 5 is moved by 
means of carrier drive device 51 in the X-direction, Y-direction or 
.theta.-direction, such that the alignment marks MA of mask M and 
alignment marks WA on the back of wafer W, which were determined and 
stored at the start, come to rest on top of one another. 
This positioning is done automatically, as was described above, by 
workpiece carrier drive device 51 controlled by control member 11 moving 
workpiece carrier 5 in the X-Y-.theta. directions. 
Positioning by the image freeze unit or the reference line generation unit 
can also be done manually, as was described above. 
Positioning of mask M relative to wafer W and preparation for exposure are 
completed with the above described sequence. 
(13) Exposure light from exposure light irradiation device 1 is emitted 
onto mask M. The mask pattern is projected onto the wafer, and thus wafer 
W is exposed. 
In the case in which the above described positioning is performed, and in 
which, after completion of the above described positioning, the next wafer 
W is placed and positioned, it being unnecessary to adjust the positions 
of objective lenses 7 and the insertion positions of optical parts L. 
Therefore, only above described positioning steps (10), (11) and (12) need 
be performed. 
However, in the case in which, as a result of changes of the ambient 
temperature, the positions of mask M and projection lens 3 change, it is 
necessary to again perform the above described steps (4), (5), (6), (7), 
(8) and (9). 
As was also described above, in this embodiment, the same effects as in the 
first and second process embodiments can be obtained. Here, it is not 
necessary that carrier drive device 51 have the function of moving 
workpiece carrier 5 in the Z-direction due to the measure by which optical 
components L are inserted and removed, by which the imaging position of 
alignment marks MA of the mask are moved, and by which the surface of 
wafer W provided with alignment marks WA is brought into agreement with 
projection surface 4 of alignment marks MA of mask M. Moreover, the 
surface of workpiece W provided with alignment marks WA can be brought 
into agreement with projection surface 4 of alignment marks MA of mask M 
by simple activation. 
In the above described third embodiment, optical components L are inserted 
into the space between projection lens 3 and the mask pattern projection 
surface 4, and the imaging positions of alignment marks MA of mask M are 
moved in the Z-direction. However, the back of wafer W and image sensors 8 
can be brought into an imaging ratio relative to one another by the fact 
that, in the first embodiment, optical components L are inserted between 
wafer W and objective lens 7 and removed, and that optical components L 
move the observation surfaces of objective lenses 7 in the Z-direction. 
This means that, in the above described first embodiment in step (3), 
optical components L are inserted, and using the alignment unit drive 
device 71, the objective lenses 7 are moved in the X-direction, 
Y-direction or Z-direction, such that the images of alignment marks MA of 
mask M are imaged on image sensors 8. 
After steps (4) through (7) have been completed, in step (8), the above 
described optical components L are removed. In this way, the back of wafer 
W and image sensors 8 can be brought into an imaging ratio relative to one 
another without moving the objective lenses 7 in the Z-direction. 
By means of the above described measure, it is unnecessary to move 
workpiece carrier 5 in the Z-direction or to move objective lenses 7. 
Therefore the device can be simplified and activation facilitated. 
Action of the Invention 
As was described above, according to the invention, the following effects 
can be obtained. 
(1) Positioning of the mask can be obtained with high precision using the 
alignment marks on the back of the workpiece and the alignment marks of 
the mask by the measure by which the positions of the alignment marks of 
the mask are determined in the state in which the workpiece is not in 
place, and in which the imaging positions of the mask pattern and the 
alignment marks agree with the focal positions of the alignment 
determination systems, by which, then, the positions of the alignment 
marks of the workpiece are determined in the state in which the workpiece 
is in place, and in which the alignment marks of the workpiece agree with 
the focal positions of the alignment determination systems, by which 
positioning of the alignment marks of the mask relative to the alignment 
marks of the workpiece is performed, by which the exposure surface of the 
workpiece, then, is brought into agreement with the imaging positions of 
the mask, by which the mask pattern is projected onto the workpiece from 
the exposure light irradiation device via the mask and the projection 
lens, and by which the workpiece is exposed. 
(2) Back alignment can be performed without moving the workpiece or the 
like by the measure by which, in above described step (1), the alignment 
determination systems are moved in a direction perpendicular to the 
workpiece exposure surface, by which the surface of the workpiece on which 
the alignment marks are recorded is thus brought into agreement with the 
focal positions of the alignment determination systems, or by which the 
imaging positions of the mask pattern and the alignment marks are moved by 
inserting and removing position correction plates. 
(3) Back alignment can be performed with high precision with a simple 
arrangement by the measure by which, in a projection exposure device which 
has an exposure light irradiation device, a mask carrier on which is 
placed a mask on which a mask pattern and alignment marks are recorded, a 
projection lens and a workpiece carrier on which a workpiece is placed, on 
the back of which (with respect to the mask patter projection surface), 
alignment marks are recorded, the workpiece carrier is provided with an 
observation window parts for observing the alignment marks of the 
workpiece, by which, furthermore, there are alignment determination 
systems for observing the alignment marks of the mask and the workpiece 
opposite the observation window parts, and by which via the observation 
window parts located on the workpiece carrier, the alignment marks on the 
back of the workpiece are observed. 
(4) Automatic alignment of the workpiece on the back of which alignment 
marks are recorded can be achieved by the measure by which, in the 
projection exposure device described above in step (3), there are an image 
processing means and a control member means by which the imaging positions 
of the projected images of the mask are determined and stored, by which 
the positions of the alignment marks recorded on the back of the workpiece 
are determined, and by which the workpiece carrier is moved such that the 
alignment marks of the mask and workpiece come to rest on top of one 
another. 
It is to be understood that although preferred embodiments of the invention 
has been described, various other embodiments and variations may occur to 
those skilled in the art. Any such other embodiments and variations which 
fall within the scope and spirit of the present invention are intended to 
be covered by the following claims.