Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-12-20
2004-03-23
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S072000
Reexamination Certificate
active
06710850
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, a pickup device, a thin film magnetic head, or another device, more particularly relates to an exposure apparatus and exposure method for exposing an image of a pattern formed on a mask on to a substrate while making the mask and substrate engage in a synchronous scan motion.
2. Description of the Related Art
In the production of a semiconductor circuit, liquid crystal display, pickup element, thin film magnetic head, or other device, the image of a fine pattern formed on a photomask or reticle (hereinafter referred to as a “mask” when spoken of in general) is repeatedly transferred using an exposure apparatus through a projection optical system to a semiconductor wafer or glass plate etc. coated with a photoresist or other photosensitive agent.
In the production of a semiconductor circuit, use is made of a step-and-repeat type reduction projection exposure apparatus (so-called “stepper”) which places the substrate on a substrate stage able to freely move in two dimensions, repeatedly makes the substrate move in steps by this substrate stage, and successively exposes and transfers the image of the pattern of the reticle on to shot areas of the substrate.
In recent years, along with the increasingly large size of substrates and increasing fineness of patterns, a step-and-scan type exposure apparatus which transfers the image of a pattern formed on a reticle to a substrate while making the substrate stage carrying the substrate and a reticle stage carrying the reticle formed with the pattern to be exposed move synchronously has come into use.
Even with exposure using the step-and-scan type exposure apparatus, like with the stepper, the photoresist or other photosensitive agent is repeatedly coated on a substrate already formed with a pattern so as to expose different patterns. Therefore, it is necessary to measure the relative position of the substrate and the pattern formed on the reticle to be projected with a high accuracy and to precisely match the relative positions of the substrate and reticle at the time of exposure. In particular, in the step-and-scan type exposure apparatus, it is necessary to accurately control the relative positions and scan speeds of the reticle and substrate at the time of start of exposure.
In the production of the device, however, in order to reduce the manufacturing costs etc., it is required to increase the number of substrates which can be processed by the exposure apparatus in a unit time (throughput). The above step-and-scan type exposure apparatus performs exposure while making the reticle and substrate engage in synchronous scan motion, but to improve the throughput, it is necessary to increase the scan speeds of the reticle stage and substrate stage at the time of exposure.
The step-and-scan type exposure apparatus moves the reticle stage and substrate stage by a constant speed at the time of exposure, so at the time of start of the scan, it is necessary to make the reticle stage and substrate stage accelerate from the stationary state to the constant scan speed, while at the time of end of the scan, it is necessary to decelerate the reticle stage and substrate stage moving at the constant scan speed to make them stop. Improvement of the throughput requires the scan speed of the reticle stage and substrate stage to be raised, but if the scan speed is raised, the acceleration at the time of acceleration or deceleration of the reticle stage also has to be made higher. Further, after the end of scan exposure of one shot area on the substrate and before the scan exposure of the next shot area, movement of the substrate is controlled so as to start the movement of the substrate in the nonscan direction perpendicular to the scan direction before the speed component relating to the scan direction in which the substrate is moved at the time of scan exposure becomes zero (stepping action) and to start the acceleration of the substrate in the scan direction before the stepping action is completed, that is, before the speed component of the substrate relating to the nonscan direction becomes zero. Therefore, the time of movement of the substrate between shot areas is shortened, so shortening of the acceleration and deceleration periods of the reticle stage, that is, an increase of the acceleration, has been requested.
If a stage moves, the position at which the substrate or reticle etc. is carried may shift. To prevent this, in the step-and-scan type exposure apparatus, the reticle is held by suction on the reticle stage, while the substrate is held by suction on the substrate stage. Therefore, even if a certain degree of force is applied to the reticle or substrate in the scan direction or the opposite direction due to acceleration or deceleration, the position of the reticle on the reticle stage and the position of the substrate on the substrate stage will not shift.
If the acceleration is increased at the time of acceleration or deceleration of the reticle stage or substrate stage, however, the position of the reticle or substrate may shift even if held by suction. The substrate is held by suction on the substrate stage over substantially the entire bottom surface, so the suction force can be made relatively high, but the reticle is a synthetic quartz or other glass plate on one surface of which a pattern is formed and illumination light for exposure passing through the reticle is projected on to the substrate, so it is only possible to hold the periphery of the bottom surface of the reticle (pattern formation surface) on the reticle stage.
Further, when providing a reduction projection type projection optical system with a projection magnification of 1/&bgr; (where &bgr; is for example 4, 5, 6, etc.), it is necessary to set the scan speed of the reticle stage to &bgr;-times the scan speed of the substrate stage. Therefore, the acceleration at the time of acceleration or deceleration of the reticle stage has to be set higher by that amount. If the reticle becomes offset, the image of the pattern formed on the reticle will be transferred to the substrate in a state with the relative positions of the reticle and substrate offset, so the device produced is liable to become a defective one which does not give the desired performance. In particular, when producing a device formed with a fine pattern, even a slight offset could lead to a defective product.
Further, in addition to the time of exposure of the substrate, for example, at the time of alignment or exchange of reticles or moving a reticle from the alignment position to an exposure position (position of start of acceleration), if the acceleration of the reticle stage is high, there is the problem that offset of the reticle will occur in the same way as above and the accuracy of alignment with the substrate will fall.
SUMMARY OF THE INVENTION
The present invention was made in consideration of this problem in the prior art and has as its object to enable exposure with a high throughput without allowing offset to occur along with movement of the mask. Further, it has as its object to enable exposure to stop being continued in a state of offset in the event that offset occurs along with movement of the mask.
To solve the above problem, according to a first aspect of the present invention, there is provided an exposure apparatus for exposing a substrate through a mask formed with a pattern, the exposure apparatus characterized by being provided with a stage which holds and moves the mask, an acceleration detection device which detects information relating to acceleration of the stage, and a control device which controls movement of the stage so that the acceleration of the stage as based on the information detected by the acceleration detection device becomes within a range of acceleration of the stage found in advance where offset will not occur in the mask.
According to the present inventi
Honda Yasuhiro
Sakamoto Hideaki
Yamaguchi Atsushi
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
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