Projection exposure apparatus having an off-axis alignment system and method of alignment therefor

Abstract

An exposure apparatus for exposing mask patterns on a sensitive plate comprises a set (for X and Y direction) of a laser interferometer for measuring a position of a wafer stage and satisfying Abbe's condition with respect to a projection lens and a set (for X and Y direction) of the laser interferometer and satisfying Abbe's condition with respect to off-axis alignment system. When a fiducial mark on the wafer stage is positioned directly under the projection lens, a presetting is performed so that measuring values by the two sets of laser interferometers are equal to each other.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a projection exposure apparatus for causing the sensitive layer coated on a substrate, such as a water for fabricating semi-conductor device and a glass plate for fabricating liquid crystal display device, to be exposed with the patterned image on a mask or reticle. More particularly, the invention relates to a projection exposure apparatus provided with an off-axis type alignment system whereby to observe mark patterns and others on a substrate through an objective optical system dedicatedly fixed outside a projection optical system or a projection optical system only.2. Related Background ArtAn example of the conventional projection exposure apparatus provided with an off-axis type alignment system (hereinafter expediently referred to as stepper) is disclosed in U.S. Pat. No. 4,452,526 or in Patent Abstracts of Japan, Vol. 2, No. 92, Jul. 28, 1978, p. 436 E78, JP-A-53-56975.Also, the fundamental c...

AI Technical Summary

Benefits of technology

It is an object of the present invention to improve the total accuracy of a projection exposure apparatus having an off-axis alignment system.

Moreover, according to the present invention, the reticle alignment and base line measurement can be performed almost simultaneously. Therefore, even if a sequence is arranged so as to measure the base line value at each time of exchanging wafers, there is no possibility that the throughput is reduced. As a result, it becomes possible to confirm at a high speed for correction any long-term drift of the base line and the positional drift of the reticle holder resulting from the illumination of the exposure light to the reticle.

Problems solved by technology

Consequently, due to the running accuracy of the wafer stage WST, air fluctuation on the optical path of the laser beam of the laser interferometer, and other unavoidable causes, there is a limit to the improvement of the precision with which to measure the base line value.

Thus there is a limit to the increase in the speed with which to execute the base line measurement process.

Accordingly, it is considered difficult to implement the direction of the mark detection so that Abbe's error (sine error) is always zero when the off-axis alignment system OWA is used for detecting various marks.

Otherwise, errors may result inevitably.

Strictly speaking, there still remain errors in the running accuracy of the wafer stage, particularly depending on its yawing, and errors due to the air fluctuation (refraction index disturbance) in the optical path of the laser interferometers.

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