Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-03-10
2003-08-19
Braun, Fred L (Department: 2852)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S071000
Reexamination Certificate
active
06608665
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an exposure apparatus used in the lithography process for manufacturing, for example, semiconductor devices, liquid crystal display devices, thin film magnetic heads or the like, and particularly to a scanning exposure apparatus in which a mask (or a reticle) and a photosensitive substrate are moved in synchronisn with each other to thereby expose the pattern of the mask on the photosensitive substrate.
2. Related Background Art
Now, in the photolithography process for the manufacture of semiconductor devices, use is made of a projection exposure apparatus in which the pattern of a mask or a reticle (hereinafter generically referred to as the reticle) is transferred onto a semiconductor wafer having a photosensitive material (photoresist) applied thereto through a projection optical system. Recently, in order to meet the tendency of semiconductor devices toward bulkiness and minuteness, it has been desired to accomplish the enlargement of the image field of the projection optical system and an improvement in resolution. However, it is very difficult in design and manufacture to realize both of the higher resolution and wider field of the projection optical system. So, attention has been paid to a scanning type exposure apparatus in which, as disclosed, for example, in U.S. Pat. Nos. 4,747,678, 4,924,257 and 5,194,893, only a localized area on a reticle is illuminated and the reticle and a wafer are moved in synchronism with each other to thereby transfer the pattern of the reticle onto the wafer. The scanning type exposure apparatus, even if the image field of the projection optical system thereof is small, can transfer a pattern image of a large area onto the wafer and moreover can improve the resolution of the projection optical system relatively easily.
Now, in the scanning type exposure apparatus, the reticle is scanned relative to an illumination area defined by a field stop (reticle blind). Accordingly, during the start and termination of the scanning, even the outside of the pattern area on the reticle is illuminated and therefore, an unnecessary pattern may be transferred onto the wafer. To prevent the transfer of the unnecessary pattern, it would occur to mind to increase the width of a light intercepting zone which defines the pattern area, but in such case, the area of the pattern area on the reticle would become small, and this is against the desire to make the area of the transfer pattern large. Also, in a case where only one of two circuit patterns on the reticle is scanned and exposed on the wafer, a part of the other circuit pattern will be transferred onto the wafer if the width of a light intercepting zone partitioning the two circuit patterns is smaller than the width of the illumination area.
So, for example, in Japanese Patent Application Laid-Open No. 4-196513 (U.S. Ser. No. 068,101 filed on May 28, 1993), it is proposed to make each blade (light intercepting plate) of a field stop defining an illumination area on a reticle movable, drive the blades at the start and end of scanning and vary the rectangular aperture in the field stop, i.e., the width of the illumination area on the reticle in the scanning direction, thereby preventing an unnecessary pattern from being illuminated. However, in the scanning type exposure apparatus, to obtain good illuminance uniformity on the wafer (in other words, to effect highly accurate control of exposure amount), the width of the illumination area in the scanning direction must be uniform. Accordingly, it is required of the field stop that there be little unevenness in edge portions perpendicular to the scanning direction and that the two edge portions be movement-controlled while being kept sufficiently parallel to each other when the width in the scanning direction is varied. However, the edge portions of the field stop are formed by something like mechanical knife edges. That is, mechanical knife edges have the inconvenience that the shape error thereof is great and the uniformity of illuminance is reduced. Also, in movement-controlling the aforedescribed field stop in synchronism with the scanning of the reticle, it is difficult to satisfy the accuracy required of parallelism. To satisfy this, a highly accurate positioning mechanism will become necessary, and this leads to the inconvenience that the varying mechanism will become very much complicated.
Also, in a scanning type exposure apparatus using a pulse light source, it is proposed to make the intensity of light on a wafer in the scanning direction into a substantially isosceles trapezoidal shape as disclosed, for example, in U.S. Pat. No. 4,822,975, in order to reduce the irregularity of the exposure amount on the wafer.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a scanning type exposure apparatus in which good illuminance uniformity (exposure amount control accuracy) is obtained and which can transfer only a desired pattern on a mask onto a photosensitive substrate.
A first scanning type exposure apparatus according to the present invention has a light source generating illuminating light, an illuminating optical system for illuminating an illumination area on a mask by the illuminating light, and a projection optical system for projecting the image of a pattern in the illumination area onto a substrate, and the mask is scanned in a predetermined direction relative to the illumination area and the substrate is scanned in a predetermined direction relative to an exposure area conjugate with the illumination area with respect to the projection optical system, whereby the image of the pattern of the mask is scanned and exposed on the substrate. A fixed field stop for setting the illumination area on the mask to a predetermined shape and a predetermined size, and a light intercepting member for variably limiting the range of the illuminated area set on the mask by the field stop with respect to the predetermined direction are disposed on or near a plane in the illuminating optical system which is conjugate with the pattern surface of the mask. Also, the shape of the illumination area set on the mask by the field stop may preferably be set to a shape conforming to an integrated exposure amount distribution with respect to a direction perpendicular to the predetermined direction on the substrate. Further, it is preferable that the field stop be formed by coating the light-transmitting substrate with light intercepting film and the surface coated with the light intercepting film be installed at a position defocused by a predetermined amount from the plane conjugate with the pattern surface of the mask.
According to the first scanning type exposure apparatus of the present invention, immediately after the start, and immediately before the termination, of the synchronized scanning of the mask and the substrate, a part of the illumination area set on the mask by the fixed field stop protrudes outwardly of a light intercepting zone on the mask which defines the pattern area. So, the light intercepting member provided discretely from the fixed field stop is moved in synchronism with the scanning of the mask, whereby the edge portion of the projected image of the light intercepting member onto the mask is set in the light intercepting zone of the mask. Thereby, a void pattern outside the light intercepting zone is prevented from being exposed on the substrate, in other words, a part thereof is prevented from being sensitized by light passing the outside of the light intercepting zone onto the substrate. Also, when the whole of the illumination area is present in the pattern area on the mask, the illumination area has its shape and size set by the fixed field stop. Accordingly, the position control accuracy of the light intercepting member may be approximately the width of the light intercepting zone on the mask. As described above, the fixed field stop for determining the integrated exposure amount on the substrate and the light intercepting member for limi
Nishi Kenji
Suzuki Kazuaki
Braun Fred L
Miles & Stockbridge P.C.
Nikon Corporation
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