Optical element

Details Optical element Optical element

2000-03-23

2001-11-13

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With multipart element

C359S355000, C359S509000, C359S565000, C359S566000

Reexamination Certificate

active

06317274

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
This invention relates to an optical element suitably usable in an exposure apparatus, a photographing apparatus or an illumination system, for example.
Diffraction gratings are used as a spectral element in spectroscopes. A diffraction grating as such a spectral element is formed with a saw-toothed shape, called a blazed shape, and it has a very high diffraction efficiency of up to 100%.
Recently, diffractive optical elements, particularly, binary optics (BO) elements with a diffraction grating of step-like shape have attracted much attention, because of its achromatic effect and aspherical effect.
Since a binary optic element has a surface formed by microprocessing, it should be handled very carefully. On the other hand, in projection exposure apparatuses into which a binary optic element can he incorporated, contamination of an optical system becomes a critical problem. That is, when high energy light such as KrF laser (&lgr;=248 nm), ArF laser (&lgr;=194 nm) or F
2
laser (&lgr;=157 nm) is used as exposure light, due to an influence such as a surrounding ambience, for example, contaminating materials may be deposed on the surface of a binary optics. Further, conventional clean rooms are designed in regard to dust or particles only. Therefore, any decomposed matters or vaporized matters may contaminate the surface of a binary optics.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical element by which contamination of the surface thereof can be reduced or avoided.
In accordance with an aspect of the present invention, there is provided an optical element, including a first substrate having a diffractive surface; a second substrate for covering the diffractive surface to provide a shield therefor; and groove means provided at the diffractive surface and extending from a central portion to a peripheral portion thereof, for discharging or replacing a gas at the diffractive surface therethrough.
In one preferred form of this aspect of the present invention, the diffractive surface has a ring-like pattern, and the groove means extends radially from a central portion of the ring-like pattern.
The second substrate may comprise a light transmissive member adhered to the first substrate to define a tightly closed space therebetween.
The light transmissive member may be fixed by adhesion at a top surface of the optical element.
The light transmissive member may be made of a glass material having a transmissivity to deep ultraviolet rays.
The closed space may comprise one of a space replaced by an inactive gas, a reduced pressure space and a vacuum space.
Each of the first and second substrates may have an anti-reflection film.
In accordance with another aspect of the present invention, there is provided an optical element including a first substrate having a surface structure with a surface level difference; a second substrate for covering the surface structure to provide a shield therefor; and groove means provided at the surface structure and extending from a central portion to a peripheral portion thereof, for discharging or replacing a gas at the surface structure therethrough.
In one preferred form of this aspect of the present invention, the surface structure has a ring-like pattern, and the groove means extends radially from a central portion of the ring-like pattern.
The second substrate may comprise a light transmissive member adhered to the first substrate to define a tightly closed space therebetween.
The light transmissive member may be fixed by adhesion at a top surface of the optical element.
The light transmissive member may be made of a glass material having a transmissivity to deep ultraviolet rays.
The closed space may comprise one of a space replaced by an inactive gas, a reduced pressure space and a vacuum space.
Each of the first and second substrates may have an anti-reflection film.
In accordance with a further aspect of the present invention, there is provided an optical system including an optical element as recited above.
In accordance with a still further aspect of the present invention, there is provided an exposure apparatus including an optical system as recited above.
In accordance with a yet further aspect of the present invention, there is provided a device manufacturing method including an exposure process for exposing a wafer by use of an exposure apparatus as recited above, and a development process for developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 5208700 (1993-05-01), Harris et al.
patent: 5214535 (1993-05-01), Harris et al.
patent: 5602683 (1997-02-01), Straaijer et al.
patent: 5696623 (1997-12-01), Fujie et al.
patent: 6008942 (1999-12-01), Ogusu et al.
patent: 6091501 (2000-07-01), Saikanmäki et al.

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