Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-11-02
2001-07-10
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C355S071000
Reexamination Certificate
active
06259510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus for implementing the same which are suitably applied to a scanning exposure apparatus for exposing a pattern on a mask onto a photosensitive substrate by synchronously scanning the mask and the photosensitive substrate.
More particularly, the present invention relates to an exposure method and apparatus to be used in a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, a thin film magnetic head, etc.
2. Related Background Art
When a semiconductor device, a liquid crystal display device or a thin film magnetic head is to be manufactured by using a photo-lithography technology, a projection exposure apparatus which exposes a pattern of a photo-mask or a reticle (hereinafter collectively referred to as a reticle) onto a photosensitive substrate such as a wafer or a glass plate on which photo-resist is applied through a projection optical system has been used. Recently, as the size of a single chip pattern of the semiconductor device tends to increase, it is required to increase the exposure area on the photosensitive substrate so that a larger pattern of the reticle may be exposed.
In order to comply with the requirement of the increased area, a scanning projection exposure apparatus for exposing a pattern on a reticle onto a photosensitive substrate by synchronously scanning the reticle and the photosensitive substrate to an illumination area of rectangular, arcuate-or hexagonal shape (hereinafter collectively referred to as a slit illumination area) has been developed (U.S. Pat. Nos. 4,747,678, 4,924,257). In the past, as shown in U.S. Pat. No. 5,194,893, in order to define a slit illumination area on the reticle, a movable light shielding means (view field diaphragm) for determining the slit illumination area is arranged at a position which is conjugate with the reticle or in the vicinity of the reticle. The shape of the slit illumination area on the reticle and the shape of the slit illumination area on the photosensitive substrate are controlled by a design constant or an apparatus constant.
In such a prior art apparatus, the following two major problems were encountered.
In general, an illumination optical system of the projection exposure apparatus is designed to illuminate the reticle with a uniform illumination light (exposure light). Accordingly, in the scanning projection exposure apparatus, in order to assure that the uniformity in the illumination is attained on the photosensitive substrate at the time when the exposure is completed after the scanning of the reticle and the photosensitive substrate relative to the slit illumination area, the width of the slit illumination area along the scan direction must be uniform.
Assuming that X represents the scan direction to the slit illumination area and Y represents a non-scan direction perpendicular to the scan direction, if the width of the slit illumination area along the scan direction is not uniform, the parallelism of the slit illumination area
30
along the scan direction is bad as shown in
FIG. 5A
, or edges of the slit illumination area
31
along the scan direction include unevenness as shown in FIG.
6
A. In the case of
FIG. 5A
, a distribution of the exposure intensity E along the non-scan direction (Y axis) measured on the photosensitive substrate gradually increases or decreases along the Y axis as shown in FIG.
5
B. On the other hand, in the case of
FIG. 6A
, a distribution of the exposure intensity E along the non-scan direction (Y axis) measured on the photosensitive substrate varies irregularly along the Y axis as shown in FIG.
6
B.
In the present projection exposure apparatus, a design rule of less than 0.5 &mgr;m which is in a sub-micron area is used. It is reported that the uniformity of the exposure intensity required for the control of a line width in such an area is as small as ±1%. Accordingly, in order to attain a sufficient uniformity of the illumination in the scanning projection exposure apparatus, the reduced unevenness of the edge along the scan direction is required for a view field diaphragm (stop) for determining the slit illumination area, and the control of the motion in changing the width of the view field diaphragm along the scan direction while maintaining sufficient parallelism of the edge along the scan direction is required, as disclosed in Japanese Patent Application Laid-Open No. 4-196513. As a result, it is difficult to control the operation of the illumination area setting means while keeping the required precision if the view field diaphragm for defining the slit illumination area is varied in synchronism with the scan by a reason to be described later.
Further, as shown in
FIG. 7
, it is assumed that two circuit pattern areas
32
A and
32
B are arranged with a light shielding area of a width L
1
therebetween on a reticle R, and the reticle R is scanned to a slit illumination area
33
of a width L
2
along the scan direction. It is further assumed that the width L
2
of the slit illumination area
33
is larger than the width L
1
of the light shielding area between the circuit pattern areas
32
A and
32
B. In this case, if only the first circuit pattern area
32
A of the reticle R is to be exposed onto the photosensitive substrate by the scanning exposure system, a portion of the pattern of the second circuit pattern area
32
B is also transferred onto the photosensitive substrate.
In order to avoid the above problem, the width L
1
of the light shielding area on the reticle R may be set to be sufficiently large but this would result in the reduction of the area of the circuit pattern area to be transferred. Alternatively, the width L
2
of the slit illumination area
33
may be reduced in synchronism with the scan closely to the end of the exposure of the circuit pattern area
32
A as shown in Japanese Laid-Open Patent application Ser. No. 4-196513, but this would complicate the control mechanism for the variable view field diaphragm.
In the prior art projection exposure apparatus, the illumination optical system is designed to illuminate the reticle with a uniform illumination. Assuming that I (mW/cm
2
) represents an illumination on a surface of the photo-sensitive substrate (image plane illumination), S (mJ/cm
2
) represents a desired exposure intensity (sensitivity of a photosensitive material on the photosensitive substrate), D (mm) is a width of slit illumination area on the surface of the photosensitive substrate along the scan direction, and v (mm/sec) is a scan velocity of the photosensitive substrate, a required exposure time t (sec) is given by:
t=S/I=D/v
(1)
The exposure intensity S is entered by an operator and the illumination I is normally determined by the intensity of the available light source. Accordingly, in order to attain the exposure intensity S entered by the operator, it is necessary to determine the scan velocity v in accordance with the width D of the slit illumination area along the scan direction. If the exposure intensity S is so small that the scan velocity v exceeds a maximum scan velocity v
max
permitted to the apparatus, it is necessary to reduce the illumination I by dimmer means in the illumination optical system or reduce the width D of the slit illumination area along the scan direction. Assuming that M represents a projection magnification of the projection optical system, the scan velocity of the reticle is given by V/M (mm/sec).
FIGS. 11A
to
11
D show various examples of the areas corresponding to the slit illumination area on the photosensitive substrate.
FIG. 11A
shows an area
130
corresponding to a rectangular illumination area of a width D along the scan direction.
FIG. 11B
shows an area
131
corresponding to an arcuate illumination area of a width D along the scan direction.
FIG. 11C
shows an area
132
corresponding to a hexagonal illumination area of a width D along the scan direction as disclos
Adams Russell
Miles & Stockbridge P.C.
Nguyen Hung Henry
Nikon Corporation
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