Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-02-02
2003-11-11
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S077000, C356S399000
Reexamination Certificate
active
06646715
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and apparatus, and more particularly, to a scanning exposure method and apparatus for use in photolithography processes in the manufacture of semiconductor devices, image pickup devices (such as CCD), liquid crystal display devices, thin-film magnetic heads, and the like.
2. Discussion of the Related Art
In a photolithography process in the manufacture of semiconductor devices, an exposure apparatus has been used for projecting a circuit pattern on a mask (also referred to as “reticle”) onto a substrate (also referred to as “wafer” or “photosensitive substrate”). In order to transfer a large circuit pattern with high accuracy and without increasing a burden on a projection optical system of the exposure apparatus, a so-called step-and-scan type exposure apparatus (or scanning exposure apparatus) has been recently developed. In the scanning exposure apparatus, the reticle and wafer are scanned in synchronization with each other with respect to an exposing radiation flux. A portion of the reticle pattern is thus illuminated so that the entire reticle pattern is successively projected onto each short area of the wafer through the projection optical system in a scanning manner. During the exposure operation of the scanning exposure apparatus, the reticle stage and the wafer stage need to be synchronously moved relative to each other at respective constant speeds.
In a conventional scanning exposure apparatus, after reticle alignment and wafer alignment are performed the reticle stage and wafer stage are moved to respective run-up start positions. Then, the reticle and wafer stages are accelerated in the respective scanning directions up to respective target speeds. After maintaining the target speeds for a predetermined settling time, which is required to settle synchronization errors between the reticle stage (reticle) and the wafer stage (wafer) within a predetermined tolerance, the reticle and wafer stages are irradiated with exposure light at the edge of the reticle pattern and the edge of the shot area on the wafer.
As described above, the reticle and wafer stages need to travel over certain run-up distances from the respective run-up start positions before starting actual exposure. In the conventional the step-and-scan exposure apparatus, the run-up distances are determined by adding a certain margin to the sum of an acceleration distance required for acceleration of each stage and a distance over which each stage travels during the worst (longest) settling time required and accordingly is fixed to a constant value. The run-up start positions of the stages are then determined such that the stages reach their respective exposure start positions after traveling the thus determined run-up distance. Accordingly, scanning exposure is started after ensuring the synchronization errors between the reticle and wafer are held within the fixed tolerance for each shot area.
However, in most cases, the actual time (settling time) necessary for the synchronization errors to settle within the fixed tolerance after the wafer and reticle stages reach their target speeds is not constant, but depends on various conditions, such as the position of a shot area (position of wafer stage), scanning speeds, and scanning directions of the reticle stage and wafer stage, etc. When the run-up distance is determined based on the worst value of the settling time and the run-up start position of each stage is uniformly determined based on the run-up distance, the run-up distance is unnecessarily greater than the actually required run-up distance for many shot areas. This results in a low throughput (low productivity).
In the step-and-scan type scanning exposure apparatus, in particular, since scanning exposure is carried out for each of many shot areas on the wafer, the exposure time tends to be longer than that of stationary-type exposure apparatus, such as a step-and-repeat exposure apparatus (so-called stepper). Accordingly, there is a need to further improve the throughput of the scanning exposure apparatus.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a scanning exposure method and apparatus that substantially obviates the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a scanning exposure method that makes it possible to reduce run-up distances of stages for scanning exposure without increasing synchronization errors, thereby improving the throughput.
Another object of the present invention is to provide a scanning exposure apparatus that can carry out such a scanning exposure method.
A further object of the present invention is to provide a scanning exposure apparatus in which the run-up distance for each shot area is optimized to thereby improve the throughput while assuring high exposure accuracy.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a scanning exposure method according to a first aspect of the present invention includes the steps of accelerating a mask and a photosensitive substrate up to respective predetermined scanning speeds, starting projecting a part of a pattern formed on the mask onto the photosensitive substrate while a synchronization error between the mask and the photosensitive substrate is held in a predetermined tolerance, and moving the mask and the photosensitive substrate relative to each other so that the pattern of the mask is sequentially transferred to each shot area on the photosensitive substrate. In this scanning exposure method, when an exposure operation is performed with respect to a first shot area of a first photosensitive substrate, an acceleration settling time that is required for the synchronization error to settle within the tolerance is measured from a point of time when the mask and the photosensitive substrate start being accelerated, and stored, and when an exposure operation is performed with respect to a second shot area of a second photosensitive substrate, acceleration starting positions of the mask and the second photosensitive substrate are determined based on the acceleration settling time measured with respect to the first shot area.
According to the present invention, where the acceleration settling time measured for the first shot area is relatively short, the acceleration starting positions of the mask and the second photosensitive substrate are set to be relatively close to their exposure start positions. Namely, the run-up distances for the mask and photosensitive substrate may be shortened by learning the acceleration settling time from actual measurements, while ensuring that the synchronization error settles within the tolerance at the exposure start positions. This leads to reduction in the exposure time and improves the throughput. In this case, where the first photosensitive substrate is identical to the second photosensitive substrate, the acceleration settling time measured for the shot area(s) of one photosensitive substrate that has/have been exposed to light may be used for determining the acceleration starting positions (run-up distances) for the next shot area of the same substrate that is to be exposed to light.
When the first photosensitive substrate is different from the second photosensitive substrate, on the other hand, the acceleration starting positions (run-up distances) for each shot area of the second photosensitive substrate in a certain lot may be determined based on the acceleration settling time measured for all of the shot ar
Adams Russell
Kim Peter B.
Morgan & Lewis & Bockius, LLP
Nikon Corporation
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