Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-02-01
2001-06-26
Evans, Geoffrey S. (Department: 1725)
Photocopying
Projection printing and copying cameras
Step and repeat
C219S121840, C355S030000, C355S067000, C359S509000
Reexamination Certificate
active
06252648
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to an exposure apparatus which uses, as an exposure beam, short wavelength electromagnetic waves such as X-rays or ultraviolet rays from an excimer laser, for example. More specifically, the invention is concerned with such an exposure apparatus, a device manufacturing method using the same, and a method of cleaning an optical element of such an exposure apparatus.
In projection exposure apparatuses for the manufacture of semiconductor integrated circuits, light of various wavelength bands is projected as an exposure beam to a substrate. As for such an exposure beam, examples are e-line (wavelength &lgr;=546 nm), g-line (&lgr;=436 nm), h-line (&lgr;=405 nm), i-line (&lgr;=365 nm), a KrF excimer laser (&lgr;=248 nm), an ArF excimer laser (&lgr;=193 nm), and X-rays.
An exposure beam emitted from a light source is directed by way of an illumination optical system for illuminating a reticle and a projection optical system (projection lens) for imaging a fine pattern formed on the reticle upon a photosensitive substrate, whereby the fine pattern is lithographically transferred to the photosensitive substrate. In such exposure apparatuses, miniaturization of the pattern linewidth has forced further improvements of throughput and resolution. Also, an exposure beam of a higher power has been required and, on the other hand, shortening of the wavelength band of an exposure beam has been required.
It is known that when an exposure beam of i-line (wavelengths &lgr;=365 nm) or a shorter wavelength is used, due to shortening of the wavelength, impurities in the air photochemically may react with oxygen. The product (blurring material) of such a reaction may be deposited on an optical element (lens or mirror) of the optical system, causing non-transparent “blur”.
As regards such a blurring material, in a case where sulfuric acid SO
2
absorbs light energy and it is excited thereby, a typical example may be ammonium sulfate (NH
4
)
2
SO
4
produced by a reaction (oxidization) with oxygen in the air. When such ammonium sulfate is deposited on the surface of an optical element such as a lens or mirror, the above-described “blur” results. Then, the exposure beam is scattered or absorbed by the ammonium sulfate, so that the transmission factor of the optical system decreases. This causes a large decrease of light quantity (transmission factor) upon the photosensitive substrate, and thus a decrease of throughput.
Particularly, for an ArF excimer laser (193 nm) or X-rays which are in a very short wavelength region, the exposure beam may cause a strong photochemical reaction. Thus, the above-described problems are very serious.
SUMMARY OF THE INVENTION
Japanese Laid-Open Patent Application, Laid-Open No. 216000/1994 shows an arrangement wherein a barrel having mounted therein a glass member such as a lens is provided in a casing of a closed structure, and wherein the inside of the casing is filled with an inert gas, thereby to solve the problem such as described above.
However, it has been found that, in such an example using inert gas, an optical element within the barrel or casing of the illumination optical system may be contaminated by organic molecules. These molecules may be those of any solvent, for example, used during manufacturing and working processes of components of the illumination optical system and remaining on the components, or those of an adhesive agent used in the casing or barrel and evaporated therefrom.
Taking the manufacturing procedure into consideration, the environmental air may be contaminated by organic molecules coming from an adhesive agent layer between a substrate and a photoresist, for example. These molecules may enter the casing or barrel. Even if the organic molecules are at a low concentration, particles may be decomposed due to the influence of an ultraviolet beam and they may be deposited on the optical element. On that occasion, a carbon film or a film containing carbon will be produced on the element surface.
Japanese Laid-Open Patent Application, Laid-Open No. 209569/1995 shows an arrangement wherein, when an inert gas is supplied into a projection optical system, a small amount of ozone is mixed into the inert gas, such that an inert gas containing ozone is supplied to an optical system. The optical element is irradiated with an exposure beam in a gas ambience containing ozone and, due to an ozone cleaning effect, decomposition of organic molecules on the surface of the optical element as well as deposition of products of the decomposition thereon are prevented.
In this structure, however, an ozone generator having a Hg lamp is provided in a portion of an inert gas supplying line. The ozone generator produces ozone beforehand, and then the ozone is supplied into the lens holder. This structure needs use of two light sources, that is, the exposure light source and the ozone generating light source. The structure is thus complicated. Further, this creates the following dangerous possibilities. That is, ozone has a property for deteriorating an element. Therefore, the ozone generator itself may be easily damaged by the influence of ozone. Thus, there is a possibility of leakage of harmful ozone from the damaged ozone generator.
It is an object of the present invention to provide an exposure apparatus by which contamination of an optical element by organic molecules can be prevented, particularly, very simply and effectively.
It is another object of the present invention to provide a device manufacturing method using such an exposure apparatus and/or a method of cleaning an optical element of an exposure apparatus.
In accordance with an aspect of the present invention, there is provided an exposure apparatus, comprising: a light source for producing an exposure beam; an optical system having a closed space, for projecting the exposure beam to a substrate for exposure thereof; first supplying means for supplying an inert gas into the closed space of said optical system; and second supplying means for supplying one of oxygen and clean air, so that the inert gas and oxygen can be supplied to the closed space.
In accordance with another aspect of the present invention, there is provided a device manufacturing method comprising the steps of:
providing an exposure apparatus as recited above; and
performing an exposure process by use of the exposure apparatus.
In accordance with a further aspect of the present invention, there is provided a method of cleaning an optical element of an exposure apparatus for exposing a substrate with an exposure beam of ultraviolet rays or X-rays, projected thereto, said method comprising the steps of: supplying an inert gas containing a small amount of oxygen into a space in which the optical element is placed; projecting the exposure beam so that ozone is produced in the space; and removing an organic compound deposited on the optical element through a photochemical reaction by projection of the exposure beam and the produced ozone.
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: 4690528 (1987-09-01), Tanimoto et al.
patent: 4704348 (1987-11-01), Koizumi et al.
patent: 4786947 (1988-11-01), Kosugi et al.
patent: 4825247 (1989-04-01), Kemi et al.
patent: 5425045 (1995-06-01), Hamatani
patent: 5539180 (1996-07-01), Mori et al.
patent: 5559584 (1996-09-01), Miyaji et al.
patent: 5602683 (1997-02-01), Straaijer et al.
patent: 5696623 (1997-12-01), Fujie et al.
patent: 5771260 (1998-06-01), Elliott et al.
patent: 5812242 (1998-09-01), Tokuda
patent: 5838426 (1998-11-01), Shinonaga et al.
patent: 5883704 (1999-03-01), Nishi et al.
patent: 6027262 (2000-02-01), Akimoto
patent: 6-216000 (1994-08-01), None
patent: 7-209569 (1995-08-01), None
Hase Tomoharu
Yamane Yukio
Canon Kabushiki Kaisha
Evans Geoffrey S.
Fitzpatrick ,Cella, Harper & Scinto
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