Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-02-27
2003-08-12
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S053000, C355S075000
Reexamination Certificate
active
06606145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and exposure method used when producing a semiconductor integrated circuit, a liquid crystal display element, a thin film magnetic head, or another microdevice or a photomask by photolithography and to a microdevice and photomask produced using such an exposure apparatus.
2. Description of the Related Art
In photolithography, one step in the production of a microdevice, use is made of an exposure apparatus for projection exposure of an image of a pattern of a photomask or reticle (hereinafter referred to as a “reticle”) on to a substrate for exposure (semiconductor wafer or glass plate coated with a photoresist). The reticle itself used for such an exposure apparatus is sometimes produced using an exposure apparatus. In the following explanation, when necessary to differentiate between the two, the former will be referred to as a “device exposure apparatus” and the latter as a “reticle exposure apparatus”.
In such an exposure apparatus, the substrate on which the pattern is to be transferred and formed is loaded on a substrate stage by a transport system having a robot arm etc. and held by a holder provided with a plurality of support pins provided on the substrate stage. The positions at which the substrate is supported by the support pins are set to be near the outer circumference of the substrate so as not to damage the portion of the substrate on which the pattern is to be formed or are set to positions giving the minimum flexing of the substrate due to its own weight.
When simply placing a substrate on such support pins, the speed and acceleration of movement would be limited as it is necessary to prevent the positional deviation of the substrate accompanying step motion of the substrate stage. This would make the time required for movement longer and the throughput (production per unit time) lower. Therefore, the practice has been to form suction ports in the centers of the support pins for suction by negative pressure (vacuum) and to hold the substrate carried on the support pins by the support pins by applying negative pressure for suction through the suction ports.
Further, the practice has been to check if a substrate is loaded on the support pins by processing the record of operation of the exposure apparatus by a computer or by visual confirmation by the operator. In apparatuses applying a negative pressure to the substrate for suction, sometimes this is checked by detection by a pressure sensor of the change in the pressure when a substrate is being held by suction and not being held by suction.
When producing for example an ordinary reticle by such an exposure apparatus, however, a light blocking layer comprised of chrome (Cr) or another material not passing much light is formed on the surface of the glass substrate for reticle production (blank), so almost none of the exposure light passes through the substrate and there is not that much of a problem. When producing a special reticle such as a phase shift reticle (including a Shibuya-Levenson type, half tone type, and chromeless type) using a light blocking layer passing light to a certain extent, however, the exposure light passes through the substrate and is reflected at the surface of the support pins supporting the substrate and at the sample table and other structures present beneath the substrate. The reflected light exposes the exposure layer (photoresist) formed by coating on the substrate surface and sometimes cause a deterioration of the line width uniformity of the pattern or uniform deviation of the line width from the target line width.
Further, when the substrate is transported by the transport system, if dust etc. is deposited on the substrate supports of the robot arm or other portions with which the substrate comes into contact, this dust etc. will sometimes end up depositing on the substrate. In this case, if the substrate is supported by the support pins with the dust etc. in between them, the de facto height of the support pins will change and, along with this, the state of flexing of the substrate will differ individually. Therefore, for example, there is the problem that it is no longer possible to sufficiently eliminate error due to flexing using a correction value found in advance for the case of ideal flexing of the substrate due to its own weight and error will occur in the shape of the pattern formed. Further, the flatness becomes poor and the amount of the leveling operation increases which sometimes cause a fall in the throughput.
Further, in an apparatus in which the substrate is simply placed on the support pins, as explained above, the throughput falls, while in an apparatus in which the substrate is subjected to negative pressure for suction, the substrate is sometimes damaged by the suction and the substrate flexes locally by a large amount at the suction portions, so correction is difficult and a high accuracy pattern sometimes cannot be formed.
Further, for detecting if a substrate is present on the support pins, in a configuration applying negative pressure to the substrate for suction, the presence of a substrate is detected by detecting the pressure, but this cannot be done when not using a configuration applying negative pressure for suction. Further, in an apparatus where the presence of the substrate is detected by processing the record of operation of the transport system by computer or by visual confirmation by the operator, the reliability is poor and sometimes substrates are doubly loaded.
SUMMARY OF THE INVENTION
A main object of the present invention is to enable the production of a high accuracy, high quality photomask or microdevice.
Another object of the present invention is to enable the reliable detection of whether a substrate has been loaded onto a holder.
According to a first aspect of the present invention, there is provided an exposure apparatus, for exposing a substrate through a mask on which a pattern is formed, provided with three first support members for supporting the substrate substantially horizontally at three locations outside of illuminated areas of the substrate.
The “illuminated areas” in this case means the pattern area at which the pattern is mainly formed and alignment mark areas (areas where alignment marks are formed) or information mark areas (areas where marks comprised of a bar code, matrix code, letters, numerals, symbol, etc. where identification information and other various information are set are formed). That is, the pattern area is the area which is illuminated by the exposure light. An alignment mark area is an area which is illuminated for optical detection of the position of the alignment mark, while an information mark area is an area which is illuminated for optical detection of the information concerned.
Since the substrate is supported by the first support members at three locations outside the illuminated areas of the substrate, even when the substrate to be exposed is a light transmitting substrate (for example, a substrate for producing a phase shift reticle), the light passing through the substrate is not reflected by the first support members to expose the exposure layer of the substrate surface. Therefore, the line width uniformity of the pattern no longer deteriorates and the line width no longer deviates uniformly from the target line width and therefore a high accuracy pattern can be formed. Further, since the substrate is supported at three points, stable support can be realized.
The positions at which the substrate is supported by the first support members are preferably set to positions in an area outside the illuminated areas giving the minimum flexing of the substrate. This is because the smallest amount of flexing possible is advantageous in processing for correction of flexing.
Alternatively, the positions at which the substrate is supported by the first support members are preferably set to positions other than positions against which second support members supporting the substrate at the time o
Irie Nobuyuki
Ishimaru Katsuaki
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
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