Projection optical apparatus using plural wavelengths of light

Abstract

A projection optical apparatus comprising a projection optical system for projectively focusing a pattern image of a mask under illumination by light of first wavelength onto a sensitive substrate, a stage holding the sensitive substrate, a fiducial plate disposed on the stage, a first mark detector for illuminating light of second wavelength different from the first wavelength, through a first mark area formed on the mask and the projection optical system, onto [the sensitive substrate or] a second mark area formed on the fiducial plate, then detecting optical information produced from the second mark area, a fourth mark area formed on [the sensitive substrate or] the fiducial plate and arranged in a predetermined positional relationship relative to the second mark area, a third mark area formed on the mask and arranged in a predetermined positional relationship relative to the first mark area, a second mark detector for illuminating the light of first wavelength onto the fourth mark area through the third mark area and the projection optical system, and then detecting optical information produced from the fourth mark area, under a condition that the first mark detector is detecting the optical information produced from the second mark area, and an error detector for detecting detection errors due to a distortion at respective positions in the view field of the projection optical system where the first mark area and the second mark area are present, based on the detected results by the first mark detector and the second mark detector.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a projection exposure apparatus used in the lithography process for semiconductor devices, liquid display devices or the like, and more particularly to an alignment apparatus which can reduce an extent of alignment errors attributable to distortion caused by a projection system of the projection exposure apparatus.2. Related Background ArtRecently, steppers mounting projection lenses of large numerical aperture thereon have been widely used as apparatus for printing a pattern of masks (reticles) on semiconductor wafers with resolution on the order of submicrons.In such a stepper, a chip pattern (shot area) already formed on the wafer and a reticle pattern newly exposed in superposed relation must be aligned with each other at overall precision less than a fraction of the minimum line width. Of late, therefore, steppers mounting alignment apparatus (sensors) with an ability of higher precision thereo...

AI Technical Summary

Benefits of technology

The present invention has been achieved in view of the various problems as stated above, and has for its object to provide a projection optical apparatus equipped with a different wavelength TTR alignment system which can detect and correct an alignment offset attributable to, particularly, a distortion with high precision.

By storing this offset amount, therefore, the error can be easily corrected when the reticle R and the wafer are later aligned with each other by using the TTR alignment system AO.sub.2X.

In this way, with the different wavelength TTR alignment system and the exposure wavelength TTR alignment system being arranged independently of each other, but to carry out the simultaneous mark detecting operation, an influence of distortion can be corrected more strictly and reliably.

Problems solved by technology

Such a correction optical system serves to maintain the reticle mark and the wafer mark in focused relation to each other under the illumination light having the different wavelength, but has suffered from an intrinsic problem that stability is insufficient and precise reproducibility cannot be obtained in the alignment.

Even if use of the two-focusing element succeeds in correcting the axial chromatic aberration, the magnification chromatic aberration cannot be always corrected satisfactorily, thereby requiring it to remove an alignment error (offset) attributable to the magnification chromatic aberration by some method.

An arrangement of the alignment optical system is complicated, which leads to a difficulty in manufacture that a severer level is required in the performance of constituent optical elements (particularly, achromatism).

In addition, it is difficult to make a match between various conditions of the optical system (such as a sigma value, number of aperture and tele-centricity) under the illumination light for exposure and various conditions of the optical system under the illumination light for alignment, thus rendering it hard to know a precise distortion error enough for practical use.

Because the distortion amount of the projection lens with respect to an ideal lattice under the illumination light for exposure is also changed depending on change in the alignment position, there has been another problem that the difference between distortion characteristics under the illumination light for alignment and the illumination light for exposure, which has been determined at only the alignment position is not enough for satisfactory correction, taking into account the fact that the reticle pattern must be superposed with the shot area over the entire wide field.

Further, the apparatus disclosed in the above cited U.S. Pat. No. 4,856,905 has a specific problem as follows.

Where the illumination light for exposure and the illumination light for alignment are separated from each other depending on their ranges of wavelength by a dichroic mirror obliquely disposed above the reticle at an angle of 45.degree., if transmissivity (or reflectivity) of the dichroic mirror for the illumination light for alignment is set very high, the illumination light for exposure to be detected by the different wavelength TTR alignment system could not pass through (or be reflected by) the TTR alignment system in its large part, making is difficult to detect the mark.

Images