Microlithographic Projection Exposure Apparatus

Abstract

A projection exposure apparatus has a projection lens (10) with an object plane (34), an image plane, an optical axis (28) and a non-telecentric entrance pupil (32). The apparatus further comprises an illumination system (12) having an intermediate field plane (80) and a field stop (36; 36). The field stop is positioned in or in close proximity to the intermediate field plane (80) and defines an illuminated field (14) in the object plane (34) that does not contain the optical axis (28) of the projection lens (24). The illumination system (12) is configured such that, in the object plane (34), a mean of the angles formed between all principal rays (42) emanating from the intermediate field plane (80) on the one hand and the optical axis (28) of the projection lens (24) on the other hand differs from 0°.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates generally to microlithographic projection exposure apparatuses comprising an illumination system and a projection lens. More particularly, the invention relates to such apparatuses in which the optical axis of the projection lens does not intersect an illuminated field on a mask that is to be projected.[0003]2. Description of Related Art[0004]Microlithography (also called photolithography) is a technology for the fabrication of integrated circuits, liquid crystal displays and other microstructured devices. More particularly, the process of microlithography, in conjunction with the process of etching, is used to pattern features in thin film stacks that have been formed on a substrate, for example a silicon wafer. At each layer of the fabrication, the wafer is first coated with a photoresist which is a material that is sensitive to radiation, such as deep ultraviolet (DUV) light. Next, the w...

AI Technical Summary

Benefits of technology

[0013]It is therefore an object of the present invention to improve the principal ray distribution provided by the illumination system in the case of projection lenses having a non-telecentric entrance pupil and an off-axis illuminated field.

[0026]It has been discovered that the introduction of a certain mean angle differing from 0° between the principal rays and the optical axis of the projection lens significantly improves the match between the principal ray distribution provided by the illumination system and the principal ray distribution required by the projection lens. This is due to the fact that the principle rays of a non-telecentric projection lens traverse obliquely an off-axis field that is to be imaged.

Problems solved by technology

However, the use of such beam splitter cubes or similar means has drawbacks, particularly in cases in which the polarization state of the projection light shall not be disturbed by the projection lens.

Thus light cannot be reflected back towards the mask.

The situation becomes more complicated, however, if the projection lens has not only a homocentric entrance pupil but also an off-axis illuminated field.

However, this considerably increases the design and manufacturing costs of the illumination system.

However, a significant mismatch of the principal ray distributions occurs if the projection lens is not telecentric, but more or less homocentric on its entrance side.

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