Supports: racks – Special article – Platelike
Reexamination Certificate
2002-07-09
2004-11-02
Friedman, Carl D. (Department: 3634)
Supports: racks
Special article
Platelike
C211S183000, C206S832000
Reexamination Certificate
active
06811040
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an apparatus for holding semiconductor wafers, the component parts of which are held together by a mechanical joint. More specifically, the present invention is directed to an apparatus for holding semiconductor wafers, the component parts of which are held together by a mechanical joint that can withstand the harsh conditions of devices used in coating semiconductor wafers.
Processing of semiconductor wafers involves harsh conditions such as exposure to corrosive conditions, high temperatures and rapid thermal cycling. Accordingly, wafer support fixtures, also known as furniture or wafer boats, need to withstand such harsh conditions. One method for processing semiconductor wafers involves rapid thermal processing (RTP). Such processes are performed in rapid thermal annealing apparatus (RTA). Semiconductor wafers are treated in an RTA from room temperature to temperatures of about 400° C. to about 1400° C. in periods of time on the order of a few seconds. The ability of such RTA systems to rapidly heat and cool a wafer from room temperature to such high temperatures in period of up to 10 seconds make them attractive for use in chemical reaction processes such as epitaxial film, amorphous silicon or polycrystalline silicon deposition.
The semiconductor industry has recognized that silicon carbide can withstand the harsh conditions involved in semiconductor processing and is a superior material for construction of wafer fixtures such as boats. Prior to silicon carbide, quartz was used as a material for wafer fixtures. However, quartz was an inadequate material for wafer fixtures because of the harsh process reaction environment as in RTP systems and the thermal incompatibility with materials used in wafer manufacture.
U.S. Pat. No. 4,978,567 to Miller discloses a silicon carbide wafer fixture employed in an RTP system. The fixture of the Miller patent consists of silicon carbide and is fabricated by chemical vapor deposition of the silicon carbide on a graphite substrate followed by destructive oxidation to remove the graphite. The Miller fixture is a single piece of silicon carbide, including a wafer support surface formed integrally with an annular surface surrounding the wafer support, and further including an annular sidewall for holding the wafer support surface at the proper height.
In the Miller fabrication method, the graphite interfaces with deposited silicon carbide is always formed on the backside of the wafer support section, opposite the support face designed for contact with the semiconductor wafer. As a result, there is no convenient technique for providing such a wafer support face with a precisely planar finish. Also, the Miller process does not allow the mold to be used for providing precisely detailed structural features in the support face.
U.S. Pat. No. 5,538,230 to Sibley discloses a single piece silicon carbide wafer boat that may hold multiple wafers for bulk processing. The wafer boat is a generally cylindrical shell section with an average inner radius slightly greater than the radius of wafers that are to be held in the boat. The generally concave inner surface of the boat includes at least two longitudinally uniform convex portions wherein a plurality of orthogonal slots or grooves are located to provide wafer support. Since the carrier is used in a horizontal position, each of the wafers is thereby supported in a vertical position, parallel to each other. The boat walls have a substantially uniform thickness except for the areas where the wafer slots are located.
The boat is made by chemically vapor depositing (CVD) silicon carbide on a graphite mold. The resulting silicon carbide shell is separated from the graphite mold by destructively burning away the mold whereby only the deposited shell remains. The orthogonal slots or grooves are machined into the shell to provide the wafer support points. Other features of the boat, such as length, height and width of the bottom and base widths may be shaped by grinding. Although post-deposition machining of a monolithic CVD-silicon carbide sheet or block may be used to form the desired object, such machining is difficult. Silicon carbide, especially theoretically dense (entirely non-porous) CVD silicon carbide, is very hard and renders machining difficult and costly. Thus, a silicon carbide boat that may be employed for bulk processing of wafers with a minimal amount of machining is highly desirable.
Fabricating semiconductor furniture from a plurality of CVD silicon carbide parts also presents a number of difficulties. Specialized applications to which CVD silicon carbide articles are often employed require that any bonds between the parts withstand extremes, such as temperature extremes. Thus, in fabricating semiconductor furniture from a plurality of CVD silicon carbide parts substantially all organic-based adhesives are entirely unsuitable because they decompose far below the semiconductor processing temperatures.
Several techniques have been proposed to bond silicon carbide parts or components. These include direct bonding (T. J. Moore, “Feasibility Study of the Welding of SiC”,
J Amer. Ceram. Soc
., 68, C151-153 (1985).), codensification of interlayers and green bodies (C.H. Bates, et al. “Joining of Non-Oxide Ceramics for High-Temperature Applications,”
Amer. Ceram. Soc. Bull
., 69, 350-356 (1990)), hot pressing of suitable silicon carbide powders (T. Iseki, K. Arakawa and H. Suzuki, “Joining of Dense Silicon Carbide by Hot Pressing,”
J. Mater. Sci. Letters
, 15, 1049-1050 (1980)), bonding with polymeric precursors (S. Yajima, et al., “Joining of Silicon Carbide to Silicon Carbide Using Polyborosiloxane,”
Amer. Ceram. Soci. Bull
., 60, 253 (1981)), brazing (J. A. P. Gehris, “High Temperature Bonding of Silicon Carbide,” M.S. Thesis, New Mexico Institute of Mining and Technology, Socorro, N. Mex. (1989)), reactive metal bonding (S. Morozumi, ete al., “Bonding Mechanism Between Silicon Carbide and Thin Foiuls of Reactive Metals,”
J. of Mater. Sci
. 20, 2976-3982 (1985)), “pressurized combustion reaction”, reaction with and without the use of tape (H. B. Rabin, “Joining of SiC/SiC Composites and Dense SiC Using Combustion Reaction in the Ti—C—Ni System,”
J. Amer. Ceram. Soc
., 75, 131-135 (1992)), and microwave joining (I. Ahmed and R. Silberglitt, “Joining Ceramics Using Microwave Energy,”
Mat. Res. Soc. Symp. Proc
., 314, 119-130 (1993)). These techniques have limited utility for semiconductor applications due to one or more drawbacks, such as use of filler material which can contaminate the furnace environment, inability of joints to withstand high service temperatures, and the need for very high temperatures or pressures during joining processing. Furthermore, most of these do not concentrate on male/female joints, where, for example, a rod is inserted into a hole and then bonding is performed. Such male/female joints are particularly desirable for fabricating wafer carriers and other furnace components for the semiconductor industry.
A male/female joint broadly defined is a joint in which an inserted (male) member is received within and bonded to a receiving (female) member. An example of a male/female joint is a joint in which the sidewalls of the male and female members are substantially parallel to each other. Such a male/female joint may be a rod inserted, for example, in a receiving closed-end bore or a sheet having parallel sides inserted in a receiving slot or groove. In bonding such a joint, it is desirable that bonding be effected between the sidewalls to provide good stability to the manufactured article. Unlike a butt joint, it is difficult to provide adequate pressure along the sidewalls of the male and female members to secure the male and female members together.
U.S. Pat. No. 5,683,028 to Goela et al. discloses a chemical means of securing a male/female joint in a silicon carbide boat. The boat in composed of four monolithic silicon carbide rods with a plurality of slits or grooves to retain multiple semiconduct
Burns Lee E.
Goela Jitendra S.
Payne Thomas
Pickering Michael A.
Friedman Carl D.
Novosad Jennifer E.
Piskorski John J.
Rohm and Haas Company
LandOfFree
Wafer holding apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wafer holding apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wafer holding apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3363647