Title: Projection exposure apparatus
Abstract: A scanning exposure apparatus includes a masking blade provided between an optical integrator and an optical system, and which is movable in a predetermined direction on a plane perpendicular to an optical axis of the optical system. The masking blade has a pair of edges substantially parallel to each other and perpendicular to the predetermined direction in the plane, and is moved so that the pair of edges are respectively imaged at a beginning and an end of scanning exposure onto a light shielding border by the optical system to change a width of an illuminated region with respect to a scan direction at both the beginning and the end of the scanning exposure.
Patent Number: 6,900,879 Issued on 05/31/2005 to Nishi
| Inventors:
|
Nishi; Kenji (Yokohama, JP)
|
| Assignee:
|
Nikon Corporation (Tokyo, JP)
|
| Appl. No.:
|
721425 |
| Filed:
|
November 26, 2003 |
Foreign Application Priority Data
| Current U.S. Class: |
355/53; 355/67; 355/71 |
| Intern'l Class: |
G03B 027/42; G03B027/54; G03B027/72 |
| Field of Search: |
355/50,53,54,55,67,71,72,74,75,77
250/491.1,492.2
|
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|
Primary Examiner: Fuller; Rodney
Attorney, Agent or Firm: Oliff & Berridge PLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a division of application Ser. No. 10/199,324 filed Jul.
22, 2002, now U.S. Pat. No. 6,707,536 which is a division of application Ser. No.
09/572,560 filed May 16, 2000, now U.S. Pat. No. 6,462,807, which is a continuation
of application Ser. No. 09/195,989 filed Nov. 20, 1998, now abandoned, which is
a division of application Ser. No. 08/906,429 filed Aug. 5, 1997, now U.S. Pat.
No. 5,854,671, which is a continuation of application Ser. No. 08/547,147 filed
Oct. 24, 1995, now abandoned which is a continuation-in-part of application Ser.
No. 08/254,672 filed Jun. 6, 1994 (now U.S. Pat. No. 5,473,410), which is a continuation
of application Ser. No. 08/068,101 filed May 28, 1993 (now abandoned).
Claims
1. A scanning exposure apparatus which transfers a pattern in a rectangular area
defined by a light shielding border on a first object onto a photosensitive second
object through a projection system by synchronously moving the first and second
objects, comprising:
an illumination system, including an optical integrator and an optical system
provided on an optical axis common to said projection system, which illuminates
a region perpendicular to the optical axis with a radiation from the optical integrator
through the optical system so that the radiation is generated on said first object
moved in a scan direction during a scanning exposure of said second object with
the radiation from said first object through said projection system by said synchronous
movement; and
a masking blade provided between said optical integrator and said optical system
to be movable in a predetermined direction on a plane perpendicular to said optical
axis, which has a pair of edges substantially parallel to each other and perpendicular
to the predetermined direction in the plane, and is moved so that the pair of edges
are respectively imaged at a beginning and an end of said scanning exposure onto
said light shielding border by said optical system to change a width of said illuminated
region with respect to said scan direction at both the beginning and the end of
said scanning exposure.
2. An apparatus according to claim 1, wherein said illuminated region contains
said optical axis and extends in a non-scan direction perpendicular to said scan direction.
3. An apparatus according to claim 2, wherein said illuminated region is axially
centered in a circular image field of said projection system and is substantially rectangular.
4. An apparatus according to claim 2, wherein said illuminated region diametrically
extends in a circular image field of said projection system and is substantially rectangular.
5. An apparatus according to claim 2, wherein the width of said illuminated region
at a middle of said scanning exposure is substantially constant and broader than
that of first and second portions of said light shielding border parallel to said
non-scan direction with respect to said scan direction.
6. An apparatus according to claim 5, wherein said masking blade is moved so
that one of said pair of edges is imaged onto said first portion at the beginning
of said scanning exposure and the other of said pair of edges is imaged onto said
second portion at the beginning of said scanning exposure.
7. An apparatus according to claim 6, wherein the width of said illuminated region,
in said scan direction, is gradually increased at the beginning of said scanning
exposure and is gradually decreased at the end of said scanning exposure to prevent
the outside of said light shielding border from illuminating with said radiation.
8. An apparatus according to claim 2, wherein the width of said illuminated region,
in said scan direction, is gradually increased at the beginning of said scanning
exposure and is gradually decreased at the end of said scanning exposure to prevent
the outside of said light shielding border from illuminating with said radiation,
and is substantially constant at a middle of said scanning exposure.
9. An apparatus according to claim 2, wherein said optical system images said
each edge with an enlargement magnification onto said light shielding border, and
said plane is substantially conjugate with a surface of said first object on which
said pattern is formed with respect to said optical system.
10. An apparatus according to claim 9, wherein said illumination system includes
an optical device provided on said optical axis different from said masking blade
so that said radiation has a shape substantially rectangular on a plane different
from said plane and perpendicular to said optical axis, and said optical system
images the rectangular radiation on the different plane onto said illuminated region.
11. An apparatus according to claim 10, wherein said optical device has a shaping
portion on said different plane in which said rectangular radiation is generated
and of which an image on said predetermined plane by said optical system has a
width substantially equal to that of said illuminated region at a middle of said
scanning exposure with respect to said scan direction.
12. An apparatus according to claim 11, wherein said optical device includes
an aperture stop, having a rectangular aperture as said shaping portion, provided
adjacent to said masking blade.
13. An apparatus according to claim 9, wherein said masking blade includes a
first portion having one of said pair of edges and a second portion having the
other of said pair of edges which are separately movable from each other.
14. An apparatus according to claim 9, wherein said masking blade has another
pair of edges substantially parallel to said predetermined direction and perpendicular
to said pair of edges, each of which is imaged onto said light shielding border
by said optical system during said scanning exposure to define a width of said
illuminated region in said non-scan direction.
15. An apparatus according to claim 14, wherein said masking blade includes plural
portions separately movable from each other on which said pair of edges and said
another pair of edges are provided.
16. An apparatus according to claim 2, further comprising a stage system having
a first stage provided at one side of said projection system to move said first
object and a second stage provided at the other side of said projection system
to move said second object, and separately moving the first and second stages from
each other to synchronously move said first and second objects during said scanning exposure.
17. An apparatus according to claim 16, wherein said stage system has a first
interferometer to detect first positional information of said first stage in different
directions including said scan direction and a second interferometer to detect
second positional information of said second stage in different directions including
said scan direction, said first and second stages are moved based on the first
and second positional information during said scanning exposure.
18. An apparatus according to claim 17, wherein said first and second positional
information includes yawing information of said first and second stages respectively,
said first and second objects are relatively rotated based on the yawing information
during said scanning exposure.
19. An apparatus according to claim 18, wherein said first and second objects
are relatively rotated with respect to a predetermined point in a distribution
of said radiation.
20. An apparatus according to claim 19, wherein said predetermined point is substantially
coincident with a center of the distribution of said radiation or said optical axis.
21. A scanning exposure apparatus which transfers a pattern in a rectangular
area defined by a light shielding border on a first object onto a photosensitive
second object through a projection system by synchronously moving the first and
second objects, comprising:
an illumination system, having an optical integrator provided on an optical axis
common to said projection system, which illuminates said first object with a radiation
from the optical integrator during a scanning exposure of said second object with
the radiation from said first object through said projection system by said synchronous
movement; and
a masking blade provided in a path of said radiation to be movable in a predetermined
direction on a plane perpendicular to said optical axis, which has a pair of edges
substantially parallel to each other and perpendicular to the predetermined direction
in the plane, and is separately moved from said first and second objects so that
a width of a defined region of said radiation on said second object, with respect
to a scan direction in said synchronous movement, is gradually increased at a beginning
of said scanning exposure by one of the pair of edges and is gradually decreased
at an end of said scanning exposure by the other of the pair of edges, the defined
region containing said optical axis and extending in a non-scan direction perpendicular
to the scan direction.
22. An apparatus according to claim 21, wherein said defined region is axially
centered in a circular image field of said projection system and is substantially rectangular.
23. An apparatus according to claim 21, wherein said defined region diametrically
extends in a circular image field of said projection system and is substantially rectangular.
24. An apparatus according to claim 22, wherein the width of said defined region,
with respect to said scan direction, is substantially constant at a middle of said
scanning exposure.
25. An apparatus according to claim 24, wherein said masking blade includes a
first portion having the one edge and a second portion having the other edge which
are separately movable from each other.
26. An apparatus according to claim 24, wherein said masking blade has another
pair of edges substantially parallel to said predetermined direction and perpendicular
to said pair of edges to determine a width of said defined region with respect
to said non-scan direction.
27. An apparatus according to claim 26, wherein said masking blade includes plural
portions separately movable from each other on which said pair of edges and said
another pair of edges are provided.
28. An apparatus according to claim 21, further comprising a stage system having
a first stage provided at one side of said projection system to move said first
object and a second stage provided at the other side of said projection system
to move said second object, and separately moving the first and second stages from
each other to synchronously move said first and second objects during said exposure.
29. An apparatus according to claim 28, wherein said stage system has a first
interferometer to detect first positional information of said first stage in different
directions including said scan direction and a second interferometer to detect
second positional information of said second stage in different directions including
said scan direction, said first and second stages are moved based on the first
and second positional information during said scanning exposure.
30. An apparatus according to claim 29, wherein said first and second positional
information includes yawing information of said first and second stages respectively,
said first and second objects are relatively rotated based on the yawing information
during said scanning exposure.
31. An apparatus according to claim 30, wherein said first and second objects
are relatively rotated with respect to a predetermined point in a distribution
of said radiation.
32. An apparatus according to claim 30, wherein said predetermined point is substantially
coincident with a center of the distribution of said radiation or said optical axis.
33. An apparatus according to claim 22, wherein said masking blade is provided
between said optical integrator and said first object and gradually changes a width
of said radiation on said first object with respect to a said scan direction at
both the beginning and the end of said scanning exposure.
34. A scanning exposure apparatus which transfers a pattern in a rectangular
area defined by a light shielding border on a first object onto a photosensitive
second object through a projection system by synchronously moving the first and
second objects, comprising:
an illumination system, having an optical integrator provided on an optical axis
common to said projection system, which illuminates said first object with a radiation
from the optical integrator during a scanning exposure of said second object with
the radiation from said first object through said projection system by said synchronous
movement;
a stage system having a first stage provided at one side of said projection system
to move said first object, a second stage provided at the other side of said projection
system to move said second object, a first interferometer to detect first positional
information of said first stage in different directions including a scan direction,
and a second interferometer to detect second positional information of said second
stage in different directions including said scan direction, which moves the first
and second stages based on the first and second positional information to synchronously
move said first and second objects during said scanning exposure; and
a masking blade provided in a path of said radiation to be movable in a predetermined
direction on a plane perpendicular to said optical axis to change a width of said
radiation on said second object with respect to said scan direction at both a beginning
and an end of said scanning exposure.
35. An apparatus according to claim 34, wherein said first and second positional
information includes yawing information of said first and second stages respectively,
said first and second objects are relatively rotated based on the yawing information
during said scanning exposure.
36. An apparatus according to claim 35, wherein said first and second objects
are relatively rotated with respect to a predetermined point in a distribution
of said radiation.
37. An apparatus according to claim 36, wherein said predetermined point is substantially
coincident with a center of the distribution of said radiation or said optical axis.
38. An apparatus according to claim 35, wherein said masking blade includes first
and second portions separately movable from each other, the first portion being
moved at the beginning of said scanning exposure, and the second portion being
moved at the end of said scanning exposure.
39. An apparatus according to claim 35, wherein said stage system has actuators
to separately move said first and second stages from each other, and further comprising
a different actuator from the actuators to separately move said masking blade from
said first and second stages.
40. A scanning exposure apparatus which transfers a pattern in a rectangular
area defined by a light shielding border on a first object onto a photosensitive
second object through a projection system by synchronously moving the first and
second objects, comprising:
an illumination system provided on an optical axis common to said projection
system to illuminate a region perpendicular to the optical axis on said first object
with a radiation from an optical integrator through an optical system during a
scanning exposure; and
a masking blade provided between said optical integrator and said optical system,
which has a pair of edges substantially parallel to each other in a plane perpendicular
to said optical axis, and is moved so that the pair of edges are respectively imaged
at a beginning and an end of said scanning exposure onto said light shielding border
by said optical system to prevent the outside of said light shielding border from
illuminating in a scan direction.
41. An apparatus according to claim 40, wherein said plane is substantially conjugate
with a surface of said first object on which said pattern is formed with respect
to said optical system, and said optical system has an enlargement magnification.
42. An apparatus according to claim 41, wherein said illuminated region is axially
centered and diametrically extends in a non-scan direction perpendicular to said
scan direction in a circular image field of said projection system, and the width
of said illuminated region in said scan direction is substantially constant at
a middle of said scanning exposure.
43. An apparatus according to claim 42, wherein said illumination system includes
an optical device provided on said optical axis different from said masking blade
so that said radiation has a shape substantially rectangular on a plane different
from said plane and perpendicular to said optical axis, and said optical system
images the rectangular radiation on the different plane onto said illuminated region.
44. An apparatus according to claim 41, further comprising a stage system having
a first stage provided at one side of said projection system to move said first
object and a second stage provided at the other side of said projection system
to move said second object, and separately moving the first and second stages from
each other to synchronously move said first and second objects during said scanning exposure.
45. An apparatus according to claim 44, wherein said stage system has a first
interferometer to detect first positional information of said first stage in different
directions including said scan direction and a second interferometer to detect
second positional information of said second stage in different directions including
said scan direction, said first and second stages are moved based on the first
and second positional information during said scanning exposure.
46. An apparatus according to claim 45, wherein said first and second positional
information includes yawing information of said first and second stages respectively,
said first and second objects are relatively rotated based on the yawing information
during said scanning exposure.
47. An illumination apparatus provided in an scanning exposure apparatus which
transfers a pattern in a rectangular area defined by a light shielding border on
a first object onto a photosensitive second object through a projection system
by synchronously moving the first and second objects, comprising:
an illumination system, having an optical axis perpendicular to a rectangular
region on a predetermined plane in which orthogonal first and second directions
are defined and on which said pattern is placed, that includes an optical integrator
and an optical system on the optical axis to illuminate the rectangular region
with a radiation from the optical integrator through the optical system and defines
the rectangular region to contain the optical axis and to extend in the second
direction so that the radiation is generated on said first object moved in the
first direction during a scanning exposure; and
a masking blade provided between said optical integrator and said optical system
to be movable in a predetermined direction on a plane perpendicular to said optical
axis, which has a pair of edges substantially parallel to each other and perpendicular
to the predetermined direction in the plane so that the pair of edges are respectively
imaged at a beginning and an end of said scanning exposure onto said light shielding
border by said optical system by moving the blade to change a width of said rectangular
region with respect to said first direction at both the beginning and the end of
said scanning exposure.
48. An apparatus according to claim 47, wherein the width of said rectangular
region with respect to said first direction is gradually increased at the beginning
of said scanning exposure and is gradually decreased at the end of said scanning
exposure to prevent the outside of said light shielding border from illuminating
with said radiation at both the beginning and the end, and is substantially constant
at a middle of said scanning exposure.
49. An apparatus according to claim 48, wherein said plane is substantially conjugate
with said predetermined plane with respect to said optical system, and said optical
system images said each edge with an enlargement magnification.
50. An apparatus according to claim 49, wherein said rectangular region is axially
centered in a circular image field of said projection system on said predetermined plane.
51. An apparatus according to claim 50, wherein said illumination system includes
an optical device provided on said optical axis different from said masking blade
so that said radiation has a shape substantially rectangular on a plane different
from said plane and perpendicular to said optical axis and said optical system
images the rectangular radiation on the different plane onto said predetermined plane.
52. An apparatus according to claim 51, wherein said optical device has a shaping
portion on said different plane in which said rectangular radiation is generated
and of which an image on said predetermined plane by said optical system has a
width substantially equal to that of said rectangular region at the middle of said
scanning exposure with respect to said first direction.
53. An apparatus according to claim 51, wherein said optical device includes
an aperture stop, having a rectangular aperture as said shaping portion, provided
adjacent to said masking blade.
54. An apparatus according to claim 50, wherein said masking blade includes a
first portion having one of said pair of edges and a second portion having the
other of said pair of edges which are separately movable from each other.
55. An apparatus according to claim 50, wherein said masking blade has another
pair of edges substantially parallel to said predetermined direction and perpendicular
to said pair of edges to define a width of said rectangular region in said second direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection exposure apparatus for use in a
lithography step in the course of manufacturing a semiconductor element, a liquid
crystal display element, etc.
The present invention relates to a projection exposure method and a projection
exposure apparatus for use in transfer-exposure of a mask pattern onto a photosensitive
substrate when, for example, a semiconductor element, a liquid crystal display
element, or the like, is manufactured by a lithography process, and in particular,
to a projection exposure method and apparatus for effecting an exposure by switching
the step-and-repeat method with the step-and-scan method.
2. Related Background Art
This kind of projection exposure apparatus has hitherto been classified roughly
into two types. One of them may involve the use of a method of exposing a photosensitive
substrate such as a wafer, a plate, etc. by a step-and-repeat method through a
projection optical system having an exposure field capable of including a whole
pattern of a mask (reticle). The other type may involve the use of a scan method
of effecting the exposure with a relative scan performed under mask illumination
of arched slit illumination light, wherein the mask and the photosensitive substrate
are disposed in a face-to-face relationship with the projection optical system
interposed therebetween.
A stepper adopting the former step-and-repeat exposure method is a dominant apparatus
in the recent lithography process. The stepper exhibits a resolving power, an overlap
accuracy and a throughput which are all higher than in an aligner adopting the
latter scan exposure method. It is considered that the stepper will continue to
be dominant for some period from now on into the future.
By the way, a new scan exposure method for attaining a high resolving power has
recently been proposed as a step-and-scan method on pp. 424-433 of Optical/Laser
Microlithography II (1989), SPIE Vol. 1088. The step-and-scan method is a combined
version of the scan method of one-dimensionally scanning the wafer at a speed synchronizing
therewith while one-dimensionally scanning the mask (reticle) and a method of moving
the wafer stepwise in a direction orthogonal to a scan-exposure direction.
FIG. 1 is an explanatory view showing a concept of the step & scan method. Herein,
shot regions (one chip or multi-chips) arranged in an X-direction on a wafer W
are scan-exposed by beams of arched slit illumination light RIL. The wafer W is
stepped in a Y-direction. Referring to the same Figure, arrows indicated by broken
lines represent a route of the step & scan (hereinafter abbreviated to S & S) exposure.
The shot regions undergo the same S & S exposure in the sequence such as SA
1,
S
2, . . . SA
6. Subsequently, the same S & S exposure is performed
on the shot regions in the sequence such as SA
7, SA
8, . .
. SA
12 arranged in the Y-direction at the center of the wafer W. In
the aligner based on the S & S method disclosed in the above-mentioned literature,
an image of the reticle pattern illuminated with the arched slit illumination light
RIL is formed on the wafer W via a ¼ reduction projection optical system.
Hence, an X-directional scan velocity of the reticle stage is accurately controlled
to a value that is four times the X-directional scan velocity of the wafer stage.
Further, the reason why the arched slit illumination light RIL is employed is to
obtain such advantages that a variety of aberrations become substantially zero
in a narrow (zonal) range of an image height point spaced a given distance apart
from the optical axis by using a reduction system consisting of a combination of
a refractive element and a reflex element as a projection optical system. One example
of such a reflex reduction projection system is disclosed in, e.g., U.S. Pat. No. 4,747,678.
Proposed in, e.g., Japanese Patent Laid-open Application No. 2-229423 (U.S.
Pat. No. 4,924,257) is an attempt to apply a typical projection optical system
(full field type) having a circular image field to an S & S exposure method other
than the above-described S & S exposure method which uses the arched slit illumination
light. The following are particulars disclosed in this Patent Laid-open Application.
Exposure light with which the reticle (mask) is illuminated takes a regular hexagon
inscribed to a circular image field of a projection lens system. Two face-to-face
edges of the regular hexagon extend in a direction orthogonal to the scan-exposure
direction. It is thus attained the S & S exposure exhibiting a more improved throughput.
That is, this Patent Laid-open Application shows that the scan velocities of the
reticle stage and of the wafer stage can be set much higher than by the S & S exposure
method using the arched slit illumination light by taking an as large reticle (mask)
illumination region in the scan-exposure direction as possible.
According to the above-described prior art disclosed in Japanese Patent
Laid-open Application No. 2-229423, the mask illumination region is enlarged in
the scan-exposure direction to the greatest possible degree. This is therefore
advantageous in terms of the throughput.
By the way, there is nothing but to take the zig-zag S & S method shown in FIG.
1 even in the apparatus disclosed in the above-mentioned Patent Laid-open Application
in consideration of actual scan sequences of mask stage and the wafer stage.
The reason for this is given as follows. A diameter of the wafer W is set to
150 mm (6 inch). When trying to complete the exposure of one-row shot regions corresponding
to the wafer diameter by only one continuous X-directional scan, the premise is
that a ⅕ projection lens system is employed. Based on this premise, a scan-directional
(X-directional) length is as long as 750 mm (30 inch). It is extremely difficult
to manufacture this kind of reticle. Even if such a reticle can be manufactured,
a stroke of the reticle stage for scanning the reticle in the X-direction requires
750 mm or more. Therefore, the apparatus invariably highly increases in size. For
this reason, there is no alternative but to perform the zig-zag scan even in the
apparatus disclosed in the above-mentioned Patent Laid-open Application.
It is therefore required that the periphery of the pattern region on the reticle
be widely covered with a light shielding substance so as not to transfer the reticle
pattern within an adjacent shot region with respect to, e.g., the shot regions
SA
1, SA
12 shown in FIG.
1.
FIGS. 2A and 2B each illustrate a layout of a hexagonal illumination region
HIL, a circular image field IF of the projection lens system and a reticle R during
a scan exposure. FIG. 2A shows a state where the hexagonal illumination region
HIL is set in a start-of-scan position on the reticle R. Only the reticle R one-dimensionally
moves rightward in the same Figure from this state. FIG. 2B illustrates a state
at the end of one scanning process.
Referring to FIGS. 2A and 2B, the symbols CP
1, CP
2,
. . . CP
6 represent chip patterns formed in row in the X-direction on
the reticle R. A row of these six chip patterns correspond to the shot regions
to be exposed by one scanning process in the X-direction. Note that in the same
Figures, the central point of the hexagonal illumination region HIL coincides substantially
with the center of the image field, i.e., an optical axis AX of the projection
lens system.
As obvious from FIGS. 2A and 2B, the light shielding substance equal to or larger
than at least a scan-directional width dimension of the hexagonal illumination
region HIL is needed for the exterior of the pattern region in the start- and end-of-scan
areas on the reticle R. Simultaneously, a scan-directional dimension of the reticle
R itself also increases. An X-directional moving stroke of the reticle stage is
also needed corresponding to a total of an X-directional dimension of the entire
patterns CP
1-CP
6 and a scan-directional dimension of the
hexagonal illumination region HIL. Those are thinkable problems in terms of shaping
up an apparatus.
Also, since being optimized for either the step-and-repeat method or the step-and-scan
method, the prior-art projection exposure apparatus unavoidably has disadvantages
of each of the methods. The disadvantages belonging to the two methods are described
in the following.
A. Step-and-Repeat Method
1. In order to increase an area for patterns to be transferred on the reticle,
it is necessary to increase a lens diameter of the projection optical system. Thus,
the increase of the area is limited together when the manufacturing cost of the
projection optical system increases.
2. Since an exposure field to be effected by the projection optical system is
in the shape of a square substantially inscribed to an effective exposure field,
a distortion of said exposure field becomes larger and an overlap accuracy is deteriorated
when the exposure is effected on a layer having a different wafer by use of a different
projection exposure apparatus (matching).
3. since the area of an exposure field to be exposed simultaneously is large
and
an exposure energy (a degree of illuminance) per unit area is small, it is necessary
to prolong the exposure time when a resist having a low sensitivity is used, whereby
a throughput is decreased.
B. Step-and-Scan Method
1. Though the projection optical system can be manufactured at low cost, the
manufacturing
cost of a stage mechanism becomes high since it is necessary to scan the reticle
and the wafer in synchronization. Moreover, when a resist having a high sensitivity
is used, it is necessary to shorten the exposure time. For this reason, the scan
velocity of the reticle stage is required to be higher. As a result, the manufacturing
cost increases.
2. Due to vibration at the scan-exposure time and an averaging of the distortions
in the projection optical system, the image forming performance is deteriorated.
3. When an overlap exposure is effected on different layers on the wafer by use
of a single projection exposure apparatus, a distortion becomes different for each
exposure. As a result, the overlap accuracy is deteriorated.
SUMMARY OF THE INVENTION
It is a primary object of the present invention, which has been devised in view
of the foregoing problems, to provide a projection exposure apparatus by a scan
method (or an S & S method) exhibiting an increased throughput by minimizing a
moving stroke of a reticle stage during a scan-exposure without providing a specially
wide light shielding substance along the periphery of a pattern exposure region
on a reticle (mask).
To accomplish this object, according to one aspect of the present invention,
there
is provided a projection exposure apparatus by a scan-exposure method, including
an illuminating means for illuminating a mask transfer region with illumination
light for an exposure through an aperture of a variable field stop disposed in
a position substantially conjugate to the mask. This apparatus also includes a
driving means for configuring the aperture of the variable field stop in a rectangular
shape (having edges orthogonal to a direction of the scan-exposure) and simultaneously
making variable a width of the rectangular aperture of the stop in a widthwise
direction (the scan-exposure direction) of the transfer region (pattern forming
region) on the mask.
The projection exposure apparatus further includes a control means for controlling
the driving means to change a width of the rectangular aperture of the variable
field stop in interlock with variations in position of the variable field stop
on the mask transfer region which varies due to the one-dimensional movements of
the mask stage.
Based on the conventional scan-exposure method, the mask is irradiated with
the illumination light via an aperture in a fixed shape (hexagon, arched illumination
area, etc.). According to the present invention, however, the scan-directional
width of the aperture (variable field stop) is varied interlocking with a scan
of the mask or the photosensitive substrate. The same S & S exposure method can
be therefore realized simply by sequentially narrowing the aperture width without
causing a large overrun of the mask in the start- and end-of-scan areas on the
mask. Accordingly, the overrun of the mask stage is eliminated in terms of its
necessity or extremely reduced, whereby the moving stroke of the mask stage) can
be minimized. At the same time, the width of the light shielding substance formed
along the periphery of the pattern forming region on the mask may also be small
to the same extent as that in the conventional mask. The advantage lies in a decrease
in labor for inspecting a pin hole defect in the light shielding substance (normally,
a chrome layer) during a manufacturing process of the mask.
Further, the aperture of the variable field stop is set in a shape adapted
to the pattern forming region on the mask, thereby making it possible to utilize
the apparatus also as a stepper equal to the conventional one.
Besides, an aperture position and a geometrical configuration of the variable
field stop are set to cause variations one-dimensionally, two-dimensionally or
in a rotational direction within the image field of the projection optical system.
It is thus feasible to instantaneously correspond to mask patterns of a variety
of chip sizes.
As explained above, according to the present invention, it is possible to minimize
the moving stroke of the mask (reticle) in accordance with the scan-exposure method.
A dimension of the light shielding band on the mask can also be reduced.
At the same time, the scan-directional illumination region on the mask can be
taken large, and, therefore, the throughput can be remarkably enhanced in combination
with a diminution in the moving stroke.
It is another object of the present invention, which has been devised in view
of the foregoing problems, to provide a projection exposure method capable of enjoying
the advantages of the step-and-repeat method and the step-and-scan method and capable
of compensating the disadvantages of the step-and-repeat method and the step-and-scan
method, as well as a projection exposure apparatus which can be used in embodying
such a projection exposure apparatus.
To accomplish this object, according to the present invention, there is provided
a projection exposure method which has a step-and-repeat mode and a step-and-scan
mode, to effect an exposure in either the step-and-repeat mode or the step-and-scan
by using at least one of information pieces on a layout of a plurality of shot
regions on a photosensitive substrate, a quantity of integrated exposure required
on the photosensitive substrate, configurations of these shot regions, a resolving
power required for pattern images of a mask, and an allowance for distortions.
Therefore, it is possible to realize an exposure method which can make the most
of only the advantages of both the step-and-repeat mode and the step-and-scan mode,
and is excellent in terms of all the performances including the throughput (the
number of wafers to be processed per unit time) and the image forming performance, etc.
According to the projection exposure apparatus of the present invention,
it is possible to use the above-mentioned exposure method.
According to the present invention, one of the both exposure methods is
selected in one of the following manners.
1) An exposure time for one photosensitive substrate is calculated on the basis
of a layout of the shot regions, required quantity of integrated exposure, etc.
Then, an exposure method having the shorter exposure time is selected.
2) When a configuration of the shot region exceeds the width of an effective
exposure
field of the projection-optical system with respect to a scan direction in the
step-and-scan mode, the step-and-scan mode is selected.
3) An exposure mode which can satisfy both the resolving power required for an
exposure of mask patterns and an allowance for distortions is selected.
When, for example, an exposure is effected in the step-and-scan mode for each
shot region on the photosensitive substrate, if movements among the shot regions
are conducted in a direction orthogonal to the scan direction, as indicated by
a locus, the exposure time is reduced. On the other hand, when the exposure for
each shot region is effected in the step-and-repeat mode, the movements among the
shot regions are conducted in the short-side direction, as indicated by a locus.
Then, the exposure time is reduced. Therefore, a stepping direction of the photosensitive
substrate is switched over in accordance with a selected exposure mode, whereby
the exposure time is further reduced.
Moreover, in order to make uniform a distribution of luminance on the mask,
it is preferable to dispose an optical integrator in an illumination optical system.
In this case, since a cross-sectional configuration of an optical element of the
optical integrator is substantially the same as that of an illumination region
on the mask, if the exposure mode is switched over to change the configuration
of the illumination region on the mask, the optical integrator equipped with an
optical element having a cross-sectional configuration substantially equal to the
configuration of said illumination region is used to improve the illumination efficiency.
According to the present invention, an exposure is effected in the step-and-scan
mode or the step-and-repeat mode, whichever is optimal, in accordance with a layout
of shot regions on the photosensitive substrate, or the like. Therefore, when,
for example, mask patterns to be exposed (or shot regions on the photosensitive
substrate) occupy an elongated area, the step-and-scan mode is adopted, while the
step-and-repeat mode is adopted when the sensitivity of th
