Scanning exposure apparatus

Abstract

A projection exposure apparatus for transferring a pattern formed on a mask onto a photosensitive substrate by a scanning exposure method, includes a light source for generating a light beam having a predetermined spatial coherence, an illumination optical system for receiving the light beam from the light source and illuminating a local area on the mask with the light beam, and a device for synchronously moving the mask and the photosensitive substrate so as to transfer the pattern on the mask onto the photosensitive substrate. A direction, corresponding to a higher spatial coherence of the light beam, is made to coincide with the direction of relative scanning an illumination area and the mask in the illumination area.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a scanning exposure apparatus, used in a photolithography process in the manufacture of, e.g., a semiconductor element, a liquid crystal display element, a thin-film magnetic head, or the like, for transferring a pattern on a mask onto a substrate by synchronously moving the mask (or reticle) and the substrate and, more particularly, to a scanning exposure apparatus suited for a case wherein light having a high spatial coherency (e.g., harmonics of a KrF or ArF excimer laser, YAG laser, or the like) is used.2. Related Background ArtIn the photolithography process for the manufacture of semiconductor elements, a reduction projection exposure apparatus (stepper) adopting a step-and-repeat method for transferring a pattern on a mask or reticle (to be generally referred to as a "reticle" hereinafter) onto a semiconductor wafer coated with a photosensitive material (photoresist) via a projection optical ...

AI Technical Summary

Benefits of technology

It is an object of the present invention to provide a scanning exposure apparatus which can minimize exposure amount unevenness on a photosensitive substrate due to interference fringes, even when light having a high spatial coherency is used as exposure light.

According to the first apparatus of the present invention, the direction in which the spatial coherence (degree of coherence) of the light beam is high is measured in advance in a plane perpendicular to the optical axis of the illumination optical system for guiding the light beam from the light source to the mask, and the direction with a higher spatial coherence is made to coincide with the scanning direction of the mask in the illumination area. Therefore, as shown in, e.g., FIG. 4, the illuminance distribution, in the scanning direction (X direction), in the illumination area varies at a predetermined pitch and at a relatively large amplitude, as indicated by a curve 40. On the other hand, the illuminance distribution, in the non-scanning direction (Y direction) perpendicular to the scanning direction, in the illumination area is relatively flat, as indicated by a curve 41. In this case, even when the illuminance distribution (curve 40) largely varies in the scanning direction, since the mask is scanned along the direction corresponding to a higher spatial coherence, exposure amount unevenness in the scanning direction on the photosensitive substrate after scanning exposure is remarkably reduced. Since the illumination distribution (curve 41) in the non-scanning direction is originally flat, to begin with exposure amount unevenness in the non-scanning direction on the photosensitive substrate is also very small. Therefore, even when illuminance evenness is impaired by interference fringes in the illumination area, exposure amount unevenness on the entire surface of the shot area on the photosensitive substrate can be reduced, i.e., the evenness of the exposure amount can be improved.

The illuminance distribution in the scanning direction of the illumination area is as indicated by, e.g., a curve 40 in FIG. 5A. Therefore, when the scanning direction of the mask (and the photosensitive substrate) is selected in this direction, waves of various phases are superposed on the photosensitive substrate due to relative movement between the interference fringes and the mask by scanning, as shown in FIG. 5B, whereby exposure amount unevenness caused by the interference fringes can be remarkably reduced by the accumulation effect.

According to the third apparatus of the present invention, the moving amount of the interference fringes in the relative scanning direction by the variable phase member is determined in units of, e.g., one to several pulses, in accordance with the scanning speed of the mask (and the photosensitive substrate) and a proper exposure amount of the photosensitive substrate. In this case, the moving amount of the interference fringes in the relative scanning direction by the variable phase member is determined in accordance with the relationship between the "pitch of interference fringes formed in the illumination area" and the "relative scanning speed of the illumination area and the mask", so that the contrast (residual contrast) of the accumulated light amount distribution on the photosensitive substrate after radiation of the plurality of pulse light components becomes equal to or smaller than the predetermined allowable value. Therefore, even when the relationship between the pitch of the interference fringes and the relative scanning speed changes upon a change in proper exposure amount of the photosensitive substrate, the residual contrast will never become larger than the allowable value to unduly impair exposure amount evenness.

When a one-dimensional pivot mirror (e.g., a polygonal mirror or a galvano mirror) for moving the interference fringes in only the scanning direction is used as the variable phase member, the pivot control of the pivot mirror can be realized by simple reciprocal motion if the direction (sign) of the moving amount in the relative scanning direction of the interference scanning is taken into consideration. Furthermore, when a pivot mirror which can two-dimensionally oscillate is used as the variable phase member to move the interference fringes in the illumination area additionally in the non-scanning direction perpendicular to the relative scanning direction, exposure amount unevenness in the non-scanning direction can also be reduced.

Problems solved by technology

As a result evenness of the illuminance on the reticle and wafer is impaired.

However, it is very difficult in terms of design and manufacture to realize both the high resolution and wide field of the projection optical system.

Therefore, when the scanning exposure apparatus uses light having a high spatial coherency as exposure light, it is difficult to reduce exposure amount unevenness caused by interference fringes even when the above-mentioned pivot mirror is used.

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