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Projection exposure method and apparatus capable of performing focus detection with high accuracy

a technology of focus detection and exposure method, applied in the direction of instruments, material analysis through optical means, optics, etc., can solve the problems of focus detection error, the slit image focal point is not always the most appropriate on the wafer, etc., and achieve the effect of high accuracy

Inactive Publication Date: 2001-09-11
NIKON CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

It is an object of the present invention to provide a projection exposure method and apparatus capable of performing a focus detection with high accuracy all the time even when a rugged portion exists on a substrate.
It is another object of the present invention to provide a projection exposure method and apparatus capable of making a focal point of a slit image incident on the substrate most appropriate so as to perform focus detection with a high accuracy all the time.
According to the present invention, a image forming position of the pattern image (SP) projected on the substrate by the focus detection system is obtained by effecting a relative scan with respect to the mark including two areas having different reflectivities. Obtained subsequently is a positional deviation from the position of the optical axis (AX) of the projection optical system. Based on this positional deviation, the moving device moves at least one of the slit image and the substrate, thereby aligning a measuring point on the substrate with the image forming position of the slit image. With this processing, the focus detection system can detect the focal point by making the slit image fall on a predetermined measuring point (e.g., the point-of-center of the shot area) at all times. Accordingly, even if the rugged portion exists in the shot area, the focus detection can be always effected with the high accuracy.
According to the present invention, the imaging status of the pattern image is obtained by the detection system on the basis of an output signal from the light-receiving device when the pattern image (SP) is photoelectrically detected on the light-receiving plane on the stage. The adjustment system serves to adjust the imaging status of the pattern image in such a manner that the focal point of the pattern image on the light-receiving plane is most appropriate. Therefore, the focus detection can be performed with high accuracy all the time and scattered detection errors, depending on each apparatus, can be removed.

Problems solved by technology

Further, in the conventional projection exposure apparatus, there is a scatter in terms of the imaging status (in-focus status) of the slit image on the wafer according to each projection exposure apparatus, and the focal point of the slit image is not always the most appropriate on the wafer.
There is a problem that an out-of-focus state of this slit image causes an error in focus detection.

Method used

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  • Projection exposure method and apparatus capable of performing focus detection with high accuracy
  • Projection exposure method and apparatus capable of performing focus detection with high accuracy
  • Projection exposure method and apparatus capable of performing focus detection with high accuracy

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first embodiment

Now, there has been explained the focus detection system for measuring one-point focal position in the shot area by irradiating the slit image SP with the light on the wafer W in this embodiment. The present invention can be, however, similarly employed for a focus detection system for detecting the focal points at a plurality of points within the on-wafer shot areas as disclosed in, e.g., U.S. Pat. No. 5,502,311, now abandoned. The main control system MCS measures coordinate values of (e.g., five pieces of) slit images by the same operation as that used in the preceding The main control system MCS then measures a deviation quantity of each slit image from the set position. FIGS. 8A and 8B illustrate one example of the screen display through the display unit CRT at that time. FIG. 8A is a view showing which direction and what degree each of the actual positions of the respective measuring points (A, B, C, D, E) deviates from the predetermined set position as in the same way with th...

second embodiment

Further, in the second embodiment discussed above, the position of the slit image SP is adjusted. However, the projection position of the point-of-center of the reticle R may be aligned with the position of the slit image SP by moving the reticle R. When moving the reticle R, however, there varies a spacing (a baseline quantity) between the alignment position of the shot area on the wafer W and the exposure position of that shot area. Accordingly, in the case of moving the reticle R, it is required that this baseline quantity be measured. Then, the main control system MCS memorizes a position (X-coordinate value) Xb.sub.1 in which the luminescent mark 31x on the stage ST is overlapped with the alignment mark RMx on the reticle R. Next, the main control system MCS memorizes a position (X-coordinate value) Xb.sub.2 in which an off-axis alignment system (22, 23) detects a baseline measurement mark 32x formed on the fiducial plate FM. Let .DELTA.Xb be the deviation quantity in the X-dir...

fourth embodiment

Upon completion of adjustment of the position and the focal point of the slit image SP, the program advances to the step 290 in FIG. 14 and enters the exposure step for exposing a pattern of the reticle on each shot area. An operation for this exposure step is the same as that in the foregoing

With the above-mentioned operations, the focal point of the slit image is made most appropriate on the wafer and the slit image is formed at the center of each shot area all the time. As a result, it is possible to perform a stable focus detection with a high accuracy all the time, regardless of ruggedness in the shot area.

In this embodiment, the focus detection system for measuring one focal position within the shot area by projecting one slit image SP on the wafer W was described. However, the present invention can be applied to a projection exposure apparatus, as disclosed in the U.S. Pat. No. 5,502,311 which comprises a multi-point focus detection system for performing a focus detection at ...

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Abstract

A projection exposure apparatus comprises a projection optical system for projecting a pattern of a mask on a photosensitive substrate, a stage, for holding the photosensitive substrate, movable in an optical-axis direction of the projection optical system and in a direction perpendicular to the optical axis, a position detection system for outputting a detection signal corresponding to a deviation of the projection optical system in the optical-axis direction between an imaging plane of the projection optical system and the surface of the photosensitive substrate by projecting a beam of light assuming a predetermined shape on the photosensitive substrate and, at the same time, photoelectrically detecting the reflected light from the photosensitive substrate, a fiducial member provided on the stage and having a fiducial pattern assuming a predetermined shape, and a device for detecting an irradiation position of the light beam within a plane perpendicular to the optical axis of the projection optical system on the basis of variations in intensity of a detection signal outputted from the position detection system when the fiducial pattern and the light beam are relatively moved in the predetermined direction perpendicular to the optical axis of the projection optical system.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates generally to a projection exposure apparatus and method employed in a photolithography process of manufacturing a semiconductor element and a liquid crystal display element, etc. and, more particularly, to a projection exposure apparatus and method capable of focusing on a photosensitive substrate.2. Related Background ArtIn a conventional projection exposure apparatus, when imaging a pattern of a mask (reticle) on a photosensitive substrate (wafer) through a projection optical system, it is indispensible to align a wafer surface with a pattern imaging plane, i.e., to perform focusing. In recent years, a focal depth of the projection optical system has become smaller. On the other hand, even an apparatus using t-line of a wavelength of 365 nm for an exposure illumination can obtain only a focal depth on the order of .+-.0.7 .mu.m. This is the real situation. Accordingly, a focus detection system incorp...

Claims

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Application Information

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IPC IPC(8): G03F9/00
CPCG03F9/7015G03F9/7026
Inventor WAKAMOTO, SHINJIIMAI, YUJI
Owner NIKON CORP