Catadioptric projection systems

Abstract

Catadioptric projection systems are disclosed for projecting an illuminated region of a reticle onto a corresponding region on a substrate. The systems are preferably used with ultraviolet light sources (e.g., 193 nm). The systems comprise a first imaging system, a concave mirror, and a second imaging system. The first imaging system comprises a single-pass lens group and a double-pass lens group. The single-pass lens group comprises a first negative subgroup, a positive subgroup, and a second negative subgroup. Light from the illuminated region of the reticle passes through the single-pass lens group and the double-pass lens group, and reflects from the concave mirror to pass back through the double-pass lens group to form an intermediate image of the illuminated region of the reticle. The light is then directed to the second imaging system that re-images the illuminated region of the reticle on the substrate. Alternatively, light from the single-pass lens group is reflected by a turning mirror to the double-pass lens group, wherein the light returning through the double-pass lens group continues directly to the second imaging system.

Description

[0001]This application claims the benefit of Japanese patent application no. 8-149903, filed May 20, 1996, and is a continuation in part of U.S. patent application Ser. No. 08 / 212,639, filed Mar. 10, 1994 and which issued as U.S. Pat. No. 5,636,066, U.S. patent application Ser. No. 08 / 628,165, filed Apr. 25, 1996 and which issued as U.S. Pat. No. 5,689,377, U.S. patent application Ser. No. 08 / 552,453, filed Nov. 3, 1995 and which issued as U.S. Pat. No. 5,691,802, U.S. patent application Ser. No. 08 / 429,970, filed Apr. 27, 1995 and which issued as U.S. Pat. No. 5,808,805 and is currently pending as U.S. reissue application Ser. No. 09 / 764,157, U.S. patent application Ser. No. 08 / 515,631, filed Aug. 16, 1995 and which issued as U.S. Pat. No. 5,861,997 and is currently pending as U.S. reissue application Ser. No. 09 / 766,486, which correspondingly claim priority under 35 U.S.C. Section 119(a)-(d) to Japanese patent application no. 5-051718, filed Mar. 12, 1993, Japanese patent applicat...

AI Technical Summary

Benefits of technology

[0020]In such catadioptric projection systems, the diameter of the concave mirror can be kept small, the ratio of the imaging-optical-system numerical aperture and the illumination-optical-system numerical aperture σ can be variable, and an appropriate location is available for an aperture if phase-shift masks are used. In addition, such catadioptric projection systems have high numerical apertures and hence provide sufficient irradiation to the wafer as well as conveniently long working distances.

[0022]The single-pass lens group comprises, in order starting at the reticle, a first negative subgroup, a positive subgroup, and a second negative subgroup. Single-pass optical groups with this configuration are compact, producing high-resolution images, and permit separation of incident and reflected light beams. The magnification of the first imaging system can be selected as appropriate while still maintaining excellent optical performance. Thus, the magnification of the intermediate image can be varied. Preferably, either the first imaging system or the second imaging system demagnifies the reticle. Obtaining a demagnification using the first imaging system simplifies the second imaging system.

Problems solved by technology

Purely refractive projection systems are inadequate alat ultraviolet wavelengths.

Unfortunately, combining optical elements of synthetic fused quartz and fluorite is ineffective in eliminating chromatic aberration because the Abbe numbers of synthetic quartz and fluorite are not sufficiently different.

Therefore, refractive optical systems for wavelengths less than about 300 nm suffer from unacceptable levels of chromatic aberration.

The refractive index of fluorite changes relatively rapidly with temperature and fluorite polishes poorly.

Therefore, most ultraviolet optical systems do not use fluorite, and thus exhibit uncorrected chromatic aberration.

Because the manufacture of precision aspheric surfaces is extremely difficult, a reflective projection system using an aspheric mirror is prohibitively expensive.

However, because it is symmetric, the optical system has a short working distance.

In addition, because it is difficult with this system to separate the incident light beam and the reflected light beam, a beamsplitter is required.

Consequently, the beamsplitter is large, heavy, and expensive.

Optical systems comprising more than one mirror can use fewer lenses than a purely refractive optical system, but other problems arise.

While an adjustable aperture is easily located in the irradiation optical system, a catadioptric projection system usually has no suitable location for a corresponding aperture, adjustable or not.

This limits the number of lens elements that can be inserted in the optical path, and thus limits the numerical aperture of the projection system and the total optical power available to expose the wafer.

The alignment of optical elements in a system with more than one axis is expensive and difficult, especially when high resolution is required.

Prior-art catadioptric projection systems are also difficult to miniaturize while simultaneously maintaining image quality.

In addition, in a miniaturized prior-art catadioptric projection system, the beam-separation mirror that separates the incident light beam from the reflected light beam is likely to obstruct one of these beams.

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