Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-07-28
2004-11-02
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C356S401000
Reexamination Certificate
active
06813000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and an apparatus for being used to transfer a pattern such as a mask pattern to a photosensitive substrate in the photolithography step for producing, for example, semiconductor elements, image pickup elements (for example, CCD), liquid crystal display elements, or thin film magnetic heads. Especially, the present invention is preferably used for a projection exposure apparatus of the scanning exposure type such as the step-and-scan system.
2. Description of the Related Art
For example, when the semiconductor element is produced, the reduction projection type exposure apparatus (stepper) of the step-and-repeat system (full field exposure type) has been hitherto used in many cases as an exposure apparatus for transferring a pattern on a reticle as a mask to respective shot areas on a wafer applied with photoresist. Recently, on the other hand, in order to respond to such a request that a large area circuit pattern is transferred highly accurately without exerting excessive load on the projection optical system, attention is paid to the projection exposure apparatus of the so-called step-and-scan system for successively transferring an image of a pattern on a reticle to respective shot areas on a wafer by synchronously moving the reticle and the wafer with respect to a projection optical system in a state in which a part of the pattern on the reticle is projected onto the wafer via the projection optical system.
In the case of the projection exposure apparatus of the scanning exposure type such as the step-and-scan system, it is also necessary that the exposure is performed in a state in which the surface of the wafer is adjusted or conformed (focused) with respect to the image plane of the projection optical system in the same manner as in the full field exposure type. However, in the case of the scanning exposure type, the exposure is performed while moving the surface of the wafer with respect to the exposure area defined by the projection optical system. Therefore, when any difference in level or the like exists on the surface of the wafer, it is desirable to previously detect the difference in level or the like. Accordingly, the following pre-reading control technique as been developed for the scanning exposure type, for example, as disclosed in Japanese Patent Application Laid-Open No. 6-283403, the content of which is incorporated hereinto by reference. That is, the focus position (position in the optical axis direction of the projection optical system) of the surface of the wafer is detected (pre-read) in a pre-reading area disposed on the front side in the scanning direction with respect to the exposure area. The focus position and the angle of inclination of the surface of the wafer are controlled on the basis of the result of the detection in accordance with the autofocus system and the autoleveling system.
As described above, in the conventional scanning exposure type projection exposure apparatus, the surface of the moving wafer can be focused within a predetermined allowable range with respect to the image plane in the exposure area of the projection optical system by using the pre-reading control technique. In the conventional projection exposure apparatus, for example, the system, in which a movable stage is driven in a contact manner along a guide having good straightness (hereinafter referred to as “contact type guide system”), has been principally adopted for the wafer stage for driving the wafer.
On the contrary, recently, the necessity to move the wafer at a high speed is increased in order to improve the throughput in the exposure step. Therefore, those dominantly used is the stage apparatus based on the non-contact guide system including a system in which a movable stage is arranged with an air guide (air bearing) along a guide having good flatness at least partially, and the movable stage is driven in a non-contact manner by using a linear motor, and a system in which a movable stage is supported in accordance with a magnetically floating system over a guide surface having good flatness at least partially, and the movable stage is driven in a non-contact manner by using a linear motor. The stage apparatus based on the non-contact guide system has the following many advantages. That is, for example, the stage apparatus is scarcely affected by foreign matters on the guide surface, and it is excellent in maintenance performance. Further, the vibration from a base board as a guide in the horizontal direction is hardly transmitted to the movable stage.
However, the stage apparatus based on the non-contact guide system tends to suffer from the existence of waviness having a relatively large pitch and a relatively large amplitude along the guide surface, as compared with the contact type guide system. It has been feared that the surface of the wafer as the exposure objective is defocused, even when the focusing is performed in accordance with the autofocus system and the autoleveling system by using the pre-reading control technique. That is, in the case of the conventional pre-reading control, the control is made assuming that the flatness of the running surface of the wafer stage is satisfactory from the pre-reading position for the focus position on the wafer surface to the exposure position. Therefore, it has been feared that if the flatness of the running surface is unsatisfactory, the defocus amount remains corresponding to the product of the angle of inclination of the running surface and the distance from the pre-reading position to the exposure position.
Recently, in order to respond to finer circuit patterns as the transfer objective, the numerical aperture of the projection optical system is further increased, and the depth of focus of the projected image becomes small in accordance therewith. Therefore, a situation arises, in which it is impossible to neglect the defocus amount based on the angle of inclination of the running surface of the wafer stage as described above.
Taking the foregoing points into consideration, a first object of the present invention is to provide an exposure method which makes it possible to highly accurately conform a surface of a substrate as an exposure objective to an image plane even when the substrate as the exposure objective is relatively moved with respect to an optical system such as a projection optical system, for example, when the exposure is performed in accordance with the scanning exposure system.
A second object of the present invention is to provide an exposure method which makes it possible to highly accurately conform a surface of a substrate to an image plane even when the angle of inclination of a running surface of a stage for moving the substrate is gently changed when the substrate as an exposure objective is relatively moved with respect to a projection optical system, for example, when the exposure is performed in accordance with the scanning exposure system.
A third object of the present invention is to provide an exposure apparatus in which the exposure method as described above can be used, and a high-performance device which is produced by using the exposure method as described above.
SUMMARY OF THE INVENTION
A first exposure method according to the present invention lies in an exposure method for forming a predetermined image on a substrate by using an optical system which radiates an exposure light beam onto the substrate and a substrate stage which relatively moves the substrate with respect to the optical system, wherein a surface of the substrate and an image plane of the optical system are set to be in a predetermined positional relationship in at least a part of an area in an exposure area defined by the optical system, the method comprising the steps of: measuring a height of the surface of the substrate at a measuring point disposed in front of the part of the area in the relative movement direction; and setting the positional relationship to perform exposure on the basis of infor
Mathews Alan
Nikon Corporation
Oliff & Berridg,e PLC
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