Coating apparatus – Gas or vapor deposition – Work support
Reexamination Certificate
1999-05-24
2001-03-20
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Work support
C118S729000, C118S715000, C269S021000
Reexamination Certificate
active
06203621
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to a vacuum chuck for holding thin sheet material such as a glass substrate, and to an apparatus for forming a substantially uniform coating of a substance on a thin sheet material such as a glass substrate.
Thin substrates are used to manufacture numerous items and often require high-temperature processing during the manufacturing. By way of example, thin glass solar cell wafers are utilized for satellite power supply applications and frequently are formed by coating one or more substances on the glass substrates in a high-temperature processing zone. For example, an amorphous silicon coating might be formed on a 3 to 5 mil thick glass wafer in a chemical vapor deposition process at a high temperature. The coating must be uniform over the surface of the wafer, or the resulting coated glass wafer is not usable for its intended purpose.
Present processing techniques for forming a coating on thin substrates include conveying the substrates slowly through a series of processing zones, with significantly different temperatures in each zone. By way of example, the series of processing zones may have a total length in the order of ten feet and may be divided by baffles into three or more zones, with the first zone being heated to a temperature in the order of 200° C. the second zone heated to a temperature in the order of about 600° C. and the third zone heated to a temperature in the order of about 200° C. In some processes a different substance is coated on the substrates in each zone, while in other processes a substance is coated on the substrates in only a single one of the zones. The substrates might be conveyed through these zones at speeds as slow as one foot per minute or slower. Each substrate might have a length of about 12 inches or longer. Consequently, as a substrate moves from one zone to the next, for a significant period of time a portion of the substrate is in the higher temperature zone, while the remainder of the substrate is in the lower temperature zone. During this time a significant temperature gradient exists over the length of the substrate. This temperature gradient can result in the thin substrate warping. During the deposition of substances onto the substrate, such warping can cause non-uniform layer growth across the substrate. The resulting coated substrate is unsatisfactory due to this non-uniform coating.
Vacuum chucks with rubber valves have been used in some room temperatures processing techniques. However, the rubber valves are not able to withstand the high temperatures and corrosive atmospheres encountered in chemical vapor deposition as utilized in many manufacturing processes.
SUMMARY OF THE INVENTION
The present invention is a vacuum chuck for holding thin sheet material, for example a glass substrate, during processing, including high-temperature processing. In accordance with the present invention, the vacuum chuck includes a chuck body having a gas-permeable support surface for supporting the thin sheet material. When the thin sheet material is supported on the gas-permeable support surface, a vacuum chamber is formed within the chuck body. The vacuum chamber has an inlet adapted to be coupled to a vacuum source to permit a vacuum to be drawn in the vacuum chamber upon activation of the vacuum source. A valve member is positioned in the vacuum chamber inlet, and a locking shim holds the valve member in a position closing the vacuum chamber inlet. Activation of the vacuum source results in the locking shim and valve member moving to open the vacuum chamber inlet to permit drawing of a vacuum in the vacuum chamber. The locking shim and valve member are responsive to lack of activation of the vacuum source by sealing the vacuum chamber to retain the vacuum therein, holding the thin sheet material on the gas-permeable support surface. Thus, the vacuum is retained and the thin sheet material held in position even after the vacuum source is deactivated.
Preferably, the locking shim is formed of two layers of material having different coefficients of thermal expansion to cause the locking shim to curve when heated, more firmly inserting the valve member into the vacuum chamber inlet to more firmly seal the vacuum chamber.
Further in accordance with the present invention, an apparatus for forming a substantially uniform coating of a substance on thin sheet material such as a glass substrate is provided, including a vacuum chuck as set forth above, a conveyor for conveying the vacuum chuck having the thin sheet material supported on it through a coating zone, and a source of coating material in the coating zone for forming the coating on the thin sheet material.
REFERENCES:
patent: 5671910 (1997-09-01), Davis et al.
patent: 5863338 (1999-01-01), Yamada et al.
patent: 5899445 (1999-05-01), Kimble
patent: 5937993 (1999-08-01), Sheets et al.
Boger David H.
Carberry David M.
Hirschberg Alan M.
Tran Dean
Vendura, Jr. George J.
Hassanzadeh Parviz
Mills Gregory
TRW Inc.
Yatsko Michael S.
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