Cata-dioptric reduction projection optical system

Abstract

In a cata-dioptric optical system having a combination of a reflection system and a refraction system for reduction-projecting an object on a first plane onto a second plane, a polarization beam splitter and a quarter wavelength plate are provided to split the incident light and the reflected light. The light beam directed to the polarization beam splitter is converted to a substantially collimated light beam by a first group of lenses. A second group of lenses are arranged between the polarization beam splitter and a concave reflection mirror to diverge the light beam. The light reflected by the concave reflection mirror is directed back to the polarization beam splitter with a substantially collimated state by the second group of lenses. The light beam from the second group of lenses transmitted through the polarization beam splitter is focused by a third group of lenses having a positive refraction power to form a reduced image.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to an exposure apparatus used for the manufacture of a semiconductor device, and more particularly to a cata-dioptric optical system for reduction-projecting an enlarged real element pattern on a reticle.2. Related Background ArtSemiconductor integrated circuit have been becoming finer and finer, and a higher resolution power is required for an exposure apparatus for making a pattern. In order to meet the requirement, it is necessary to shorten a wavelength of a light source and increase a numerical aperture (N.A.) of an optical system. However, as the wavelength is shortened, a glass material which can be practically used is limited due to the light absorption.When the wavelength is shorter than 300 nm, the practically usable glass materials are only synthesized quartz and fluorspar (calcium fluoride). However, because of a poor temperature characteristic of the fluorspar, it may be used in only a sma...

AI Technical Summary

Benefits of technology

It is an object of the present invention to provide a reduction projection optical system having a good focusing characteristic, which includes a cata-dioptric system.

It is preferable that the quarter wavelength plate is arranged between the polarization beam splitter and the second group of lenses. By this arrangement, the quarter wavelength plate is arranged in the substantially collimated light beam and the characteristic of the quarter wavelength plate is improved.

Problems solved by technology

However, as the wavelength is shortened, a glass material which can be practically used is limited due to the light absorption.

However, because of a poor temperature characteristic of the fluorspar, it may be used in only a small portion of optical elements of the optical system, and it is not desirable to use it in quantity.

In addition, it is very difficult to manufacture a projection optical system which meets the above requirement by only a refraction system.

It is almost impossible to manufacture a projection optical system having a large numerical of aperture by only a reflection system, because of difficulty in aberration correction.

As a result, it is difficult to increase the numerical of aperture.

Further, since it is not possible to expose an entire wafer to light when a pattern on a reticle or mask is to be transferred to the wafer, it is necessary to make the exposure while the reticle and the wafer are moved at different velocities determined by a reduction ratio of the optical system.

As a result, a mechanical construction is complex and there is a big difficulty in maintaining a precision for the transfer of a very fine pattern.

As a result, a resolution power is so low that the apparatus cannot be used as a semiconductor manufacturing exposure apparatus.

In this optical system, however, many flares exist as they do in the optical system described above, and the light loss is large and the resolution power is low because of the non-uniformity of the reflection factor at the beam splitter and the non-uniformity of the phase change to an angle of incidence caused by the absorption, characteristic and the multi-layer film.

Accordingly, it also has a big problem for practical use.