Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2000-04-25
2001-10-23
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S053000, C355S073000
Reexamination Certificate
active
06307620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to substrate holding apparatuses for holding workpieces. In particular, the present invention relates to a substrate holding apparatus used in apparatuses for making semiconductors, liquid crystal substrates, magnetic heads, micromachines and the like. The present invention also relates to an exposure apparatus and a method for making a device using the substrate holding apparatus. Moreover, the present invention relates to a method for cleaning a substrate holding section.
2. Description of the Related Art
The wavelength of exposure light sources is currently shifting from 365 nm of the i-line to 248 nm of the KrF laser. Next generation light sources of a shorter wavelength are also being developed. Laser light having a wavelength that is shorter than the wavelength of the KrF laser significantly damages optical elements, resulting in increased operation cost. Thus, in addition to the trend of light sources towards shorter wavelengths, development of high-resolution exposure apparatuses is directed to high numerical aperture (NA) projection optical systems. The effective depth of focus of the optical system, however, decreases as the NA increases. Thus, in order to achieve a sufficiently large depth of focus, the process tolerances must be maintained as much as possible by suppressing the curvature of field in the optical system and by improving the uniformity of the substrate thickness and the planar precision of a chuck.
In consideration of such circumstances, incidental incorporation of foreign materials between a wafer and the chuck must be avoided in order to assure a practical depth of focus. Various types of foreign materials, such as resists and worn parts formed by sliding of a contact portion of a transfer hand, may be adhered to the rear surface of the wafer during steps prior to the exposure steps. It is difficult to determine (1) where foreign materials are adhered and (2) the sizes of the foreign materials. Further, foreign materials interposed between the wafer and the chuck cause significant effects. For example, when a foreign material having a particle size of 1 &mgr;m is interposed, the wafer rises over a region having a diameter of 12 mm from the center of the foreign material, resulting in decreased resolution. If the foreign material remains on the chuck, wafer defects will occur at the same position on many wafers.
In conventional apparatuses, grinders provided for cleaning slide on the surface of the chuck, under pressure, in order to remove the foreign materials adhered to the chuck by directly scraping off the foreign materials. This cleaning process is performed manually or automatically and causes a decrease in throughput due to the apparatus being shut down during the cleaning process.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a means for preventing adhesion of foreign materials which causes a decrease in yield of device production, and a means for rapidly removing the foreign materials.
A substrate holding apparatus in accordance with the present invention includes a substrate holding section for holding a substrate, wherein the substrate holding section includes a thin film that causes a photocatalytic reaction upon irradiation with light.
Preferably, the substrate is held at the substrate holding section by vacuum chucking.
Preferably, the thin film is composed of a ceramic material having semiconductor characteristics. Preferably, the thin film is composed of titanium oxide. Preferably, the titanium oxide is heat-treated at 800° C. or less.
Preferably, the substrate holding section is provided on a wafer chuck.
The substrate holding apparatus may further include a pin supporting the substrate. The substrate holding apparatus may further include a projection provided on the pin.
The thin film may be formed at least at a position in contact with the substrate.
In a preferable embodiment, the thin film may be formed at the tip of the pin.
In another preferable embodiment, the thin film may be formed on the periphery of a position in contact with the substrate.
In another preferable embodiment, the thin film may be formed on the periphery of a pin supporting the substrate.
The substrate holding section may be formed at a hand of a transfer system for transferring a wafer.
Preferably, the hand is composed of a ceramic material.
Preferably, the hand is irradiated with ultraviolet rays in a waiting mode.
In another aspect of the present invention, a substrate transfer system includes the above-described substrate holding apparatus.
In another aspect of the present invention, an exposure apparatus includes the above-described substrate holding apparatus.
Preferably, the substrate holding apparatus is moved by a stage.
Preferably, exposure of the substrate holding apparatus is performed while moving the stage stepwise. Alternatively, exposure of the substrate holding apparatus may be performed while scanning a stage.
Preferably, the substrate holding apparatus is cleaned by exposure of the substrate holding apparatus.
Preferably, the substrate holding apparatus is exposed with a light beam having a wavelength of 420 nm or less. Preferably, the light beam is in the i-line.
The exposure apparatus may further include a light irradiation unit for exposing the substrate holding apparatus. In such a case, the light irradiation unit preferably introduces a light beam from a light source, the light source being used for transferring a pattern formed in a reticle onto a wafer, to expose the substrate holding apparatus.
Preferably, the light irradiation unit functions as a means for radiating a light beam for transferring a pattern formed in a reticle onto a wafer.
Preferably, the light irradiation unit exposes the substrate holding apparatus using a light source other than a light source for transferring a pattern formed in a reticle onto a wafer.
Preferably, the substrate holding section is provided in a coating unit for applying a resist solution or a developing solution onto the substrate.
In another aspect of the present invention, a coating unit includes the above-described substrate holding apparatus.
Preferably, a resist solution or a developing solution is applied onto the substrate.
In another aspect of the present invention, a method for making a device includes the steps of providing the above-described exposure apparatus, transferring a pattern formed in a reticle onto a wafer, and exposing the substrate holding apparatus with light causing a photocatalytic reaction.
The method for making a device may further include the steps of applying a resist onto the wafer using a coating unit such as discussed above, and developing the exposed wafer.
In another aspect of the present invention, a method for cleaning a substrate holding section for holding a substrate, includes the steps of moving the substrate holding section provided with a thin film that causes a photocatalytic reaction, into an irradiation region of a light irradiation unit, and irradiating the substrate holding section with light from the light irradiation unit.
Preferably, the substrate holding section is irradiated with the light by using an optical system of an exposure apparatus.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout.
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Takabayashi Yukio
Uzawa Shigeyuki
Adams Russell
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Rodney
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