Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-07-29
2001-02-20
Lee, Eddie C. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S069000
Reexamination Certificate
active
06191844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scanning projection exposure apparatus, and more particularly, to a scanning projection exposure apparatus for transferring the pattern of a mask onto a photosensitive substrate via a projection optical system while synchronously moving a mask stage for holding the mask, and a substrate stage for holding the photosensitive substrate in a predetermined scan direction.
2. Description of the Related Art
A scanning projection exposure apparatus has been known as one of exposure apparatuses for use in producing semiconductor devices or liquid crystal display devices by the photolithographic process. The scanning projection exposure apparatus, if briefly described, transfers the pattern of a reticle, as a mask, onto a photosensitive substrate via a projection optical system while synchronously scanning a reticle stage (mask stage) for holding the reticle and a substrate stage for holding the photosensitive substrate in a predetermined scan direction.
In a conventional scanning projection exposure apparatus, the reticle stage and the substrate stage were controlled by stage speed control systems assigned respective target values so that the reticle stage and the substrate stage would be synchronously scanned at a speed ratio (e.g., 4:1) determined by the projection magnification ratio of a projection optical system.
FIG. 3
shows an example of the speed versus time profile of the substrate stage during scan exposure. As shown in this drawing, the substrate stage is accelerated and reaches a target speed (0.08 m/s, herein). Then, when a predetermined stabilization time (the period of time required for the substrate stage to be synchronized with the reticle stage) has elapsed, an exposure light source is turned on for a predetermined period of time (scan exposure time) to illuminate the reticle with a constant amount of exposure light for performing exposure. After exposure is completed, a predetermined idle time is provided before the stage is decelerated from the target speed to a standstill. The target speed of the stage is determined by the sensitivity of a resist coated onto the surface of the photosensitive substrate so as to give the necessary amount of exposure. That is, the amount of exposure has been determined by the power of the exposure light source (a constant value) multiplied by the speed of the stage (a constant speed).
With this background, development of a high speed stage system is under way to shorten the exposure time and increase the throughput.
To realize such a high speed stage system, the capacity of a power amplifier should be increased to obtain a greater thrust. However, this leads to cost buildup. A laser interferometer, usually used to measure the position of the stage, should be increased in measurement accuracy with the speeding of the stage. As the moving speed of the stage rises, vibrations of the apparatus become large, adversely affecting imaging characteristics. Thus, it is not an easy task to improve the throughput by speeding up the stage.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances. Its object is to provide a scanning projection exposure apparatus capable of shortening the exposure time without making the speed of the stage high.
To attain this object, this invention has been designed to perform an exposure action not only in a constant speed zone of the stage, but also in an acceleration zone until the stage reaches its target speed, and a deceleration zone ranging from the end of the target speed to a standstill, while controlling the amount of light for exposure in an appropriate manner.
According to a first aspect of the invention, there is provided a scanning projection exposure apparatus comprising:
an exposure light source for emitting exposure light to illuminate a mask;
a mask stage for scanning the mask across an illumination region on the mask;
a projection optical system for projecting images of a pattern of the mask onto a photosensitive substrate;
a substrate stage for scanning the photosensitive substrate across an exposure region which is conjugate to the illumination region with respect to the projection optical system;
a position measuring device for measuring the position of one of the mask stage and the substrate stage;
a calculation part for calculating a target value for the amount of exposure light depending on the speed of the one stage on the basis of an output from the position measuring device; and
a light amount adjustment system for adjusting the amount of exposure light from the exposure light source in response to the target value from the calculation part.
In accordance with the scanning projection exposure apparatus of the present invention, when the scanning of the stage is started, the calculation part calculates the speed of one (e.g., the substrate stage) of the mask stage and the substrate stage on the basis of an output from the position measuring device (e.g., laser interferometer) which measures the position of the one stage (e.g., the substrate stage). At the calculation part, a target value for the amount of exposure light adapted to the stage speed is calculated so that exposure may be performed with the same amount of light over any of the acceleration period, constant speed period, and deceleration period of the stage. The light amount adjustment system adjusts the amount of exposure light from the exposure light source in response to the target value from the calculation part. Thus, exposure is carried out throughout the period from the start of drive to the halt, including the constant speed zone in the scan direction of the substrate stage, whereby exposure takes place with uniform amount of light all over those areas on the photosensitive substrate which are subjected to exposure (shot areas). Hence, the scan time is shortened, and the throughput for the production of a semiconductor device is increased.
In the scanning projection exposure apparatus of the present invention, the light amount adjustment system is preferably a closed loop control system including a light amount detector for detecting the amount of exposure light, and a controller for acting based on a light amount deviation, as an action signal, which is the difference between the output of the light amount detector and the target value of the amount of exposure light. According to this construction, the controller makes follow-up control so that the output of the light amount detector coincides with the target value. Even if the light amount adjustment system undergoes any disturbance, therefore, little influence is exerted, and exposure with appropriate amount of light takes place, regardless of the speed of the substrate stage, throughout the entire time zone from the start of drive in the scan direction of the substrate stage until its standstill.
In the present invention, the exposure light source may be an excimer laser light source which emits pulsed light. The amount of exposure light can be adjusted by modulating the number of laser pulses in response to the target value of the amount of exposure light. The excimer laser makes it easy to modulate the amount of exposure light.
According to a second aspect of the present invention, an exposure method for exposing a pattern of a mask to lead the pattern onto a photosensitive substrate, comprising:
scanning the mask across an illumination region on the mask while illuminating the mask with exposure light;
scanning the photosensitive substrate across an exposure region on the photosensitive substrate in synchronism with the scanning of the mask, the exposure region being optically conjugate to the illumination region; and
modulating the amount of exposure light in response to the moving speed of the mask or the photosensitive substrate so that the photosensitive substrate may be exposed with a uniform amount of light from the start of the scanning until completion of the scanning.
In accordance with the exposure method of the present inve
Fuller Rodney
Lee Eddie C.
Nikon Corporation
Oliff & Berridg,e PLC
LandOfFree
Scanning exposure apparatus in which light exposure is a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Scanning exposure apparatus in which light exposure is a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Scanning exposure apparatus in which light exposure is a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566816