Heating – Accessory means for holding – shielding or supporting work... – Support structure for heat treating ceramics
Reexamination Certificate
2001-07-09
2002-11-05
Wilson, Gregory (Department: 3749)
Heating
Accessory means for holding, shielding or supporting work...
Support structure for heat treating ceramics
C211S041180
Reexamination Certificate
active
06474987
ABSTRACT:
This application claims priority of Japanese Application Nos. Hei 11-249480 filed Sept. 3, 1999 and 2000-160033 filed May 30, 1999 and International Application No. PCT/JP00/05818 filed Aug. 29, 2000, the complete disclosure of which are hereby incorporated by reference.
TECHNICAL FIELD
The present invention relates to a wafer holder of a silicon wafer suitable for heat treatment of silicon wafers, and particularly suitable for high temperature anneal treatment in fabricating a SIMOX (Separation by IMplanted OXygen) wafer.
BACKGROUND ART
There has been conventionally disclosed a wafer holding apparatus including a plurality of parallelly provided support columns and wafer supporting plates mounted on the support columns, wherein a recessed cut portion is formed in each of the wafer supporting plates where a silicon wafer is loaded (Japanese Patent Application Laid-Open No. HEI-5-114645 (114645/1993)). In this apparatus, the wafer supporting plates are formed of high-melting ceramics such as SiC sintered bodies.
In the thus constructed wafer holding apparatus, wafers are placed on the wafer supporting plates mounted to the columns and are inserted into an electric furnace, so that the contacting areas between the wafer supporting plates and wafers are increased. As a result, loads are not concentrated to a partial area of each wafer, to thereby avoid plastic deformation of wafers upon heat treatment.
Further, forming the recessed cut portion in each wafer supporting plate enables a reduction of the weight of the whole apparatus and allows to move the silicon wafers into and out of the electric furnace such as by pinching the wafers by tweezers.
However, the formation of the recessed cut portion in the wafer supporting plates in the wafer holding apparatus disclosed in the aforementioned Japanese Patent Application Laid-Open No. HEI-5-114645 (114645/1993) brings the supporting plates to be out of point symmetry with respect to the centers of the supporting plates themselves, respectively, so that there is such a possibility that the wafer is warped at the recessed cut portion upon fabricating the supporting plate. Also, there is such a possibility that the silicon wafer is contacted with the edges of the recessed cut portion when the silicon wafer is placed on the wafer supporting plate, to thereby cause crystal defects called “slips” within crystals of the wafer such as due to thermal stresses upon heat treatment.
To overcome this problem, there has been disclosed a vertical semiconductor diffusion furnace aimed jig, in which the jig includes ring-shaped wafer supporting bodies made of silicon carbide substance removably mounted to columns provided between an upper plate and a lower plate (Japanese Patent Application Laid-Open No. HEI-6-163440 (163440/1994)). This jig is constituted to horizontally support peripheries of wafers by the wafer supporting bodies, respectively.
In the thus constituted vertical semiconductor diffusion furnace aimed jig, the wafer supporting bodies are uniformly arranged relative to outer peripheries of wafers and the areas of the wafer supporting bodies are increased, to thereby allow to decrease the unit surface pressure acting on the wafer supporting bodies and to disperse loads thereto. As a result, it becomes possible to avoid occurrence of slips in wafers.
However, in the conventional vertical semiconductor diffusion furnace aimed jig disclosed in the Japanese Patent Application Laid-Open No. HEI-6-163440 (163440/1994), it is difficult to evenly hold wafers at the outer peripheries thereof due to the affection of surface-pendant drops at the outer peripheral portions of wafers when the outer peripheries of wafers contact with the wafer supporting bodies, leading to a possibility of occurrence of slips in wafers.
It is therefore a first object of the present invention to provide a wafer holder capable of restricting occurrence of slips within wafers, by preventing warpage of a holder body upon fabricating the holder body.
It is a second object of the present invention to provide a wafer holder capable of restricting occurrence of slips within wafers, by inhibiting contact of an outer periphery of a wafer with the holder body.
It is a third object of the present invention to provide a wafer holder capable of assuredly holding each of wafers having different diameters without deviating them from pertinent predetermined positions, by the same holder body.
It is a fourth object of the present invention to provide a wafer holder capable of smoothly conducting working operations for loading and unloading the wafer to and from the holder body.
DISCLOSURE OF THE INVENTION
As shown in
FIGS. 1 through 3
, the invention according to claim 1 is an improvement in a wafer holder comprising a holder body
23
for carrying thereon a wafer
22
, the holder body
23
being adapted to be inserted into a plurality of holder-aimed concave recesses
14
formed on supporters
12
accommodated in a heat treatment furnace
10
such that the holder body
23
is held horizontally.
The wafer holder is characterized in: that the holder body
23
is formed into a disk shape free of recessed cut portions; that the holder body
23
is formed with an upwardly projecting ring-like projection
24
extending in the circumferential direction of the holder body
23
around the axis of the holder body
23
; that the wafer holder is constituted such that the wafer
22
is to be contacted with the upper surface of the projection
24
and is to be placed on the holder body
23
, and that the wafer holder is constituted such that the outer diameter of the projection
24
is formed to be in a range of 0.5D to 0.98D wherein D is a diameter of the wafer
22
, and such that the outer periphery of the wafer
22
is kept from contacting with the projection
24
.
According to the wafer holder recited in claim 1, the holder body
23
is formed into the disk shape free of recessed cut portions, i.e., the holder body
23
is formed in a point symmetric manner with respect to the axis of the holder body
23
, so that no warpage is caused in the holder body
23
even upon fabricating the same. As a result, each wafer
22
evenly contacts with the upper surface of the projection
24
such that substantially no internal stresses are caused within the wafer
22
. Further, the outer periphery of the wafer
22
is not contacted with the holder body
23
and it is possible to evenly hold the wafer
22
without the affection of surface-pendant drops of the outer peripheral portion of the wafer
22
, so that no slips are caused within the wafer
22
.
In the present specification, it is noted here that the term “recessed cut portion” means a notch or cutout reaching the vicinity of the center of the holder body, and such a term never embraces those recesses formed at slight depths at the outer periphery of the holder body. In other words, the term “recessed cut portion” used in the above never embraces those recesses which are small to such an extent not to cause warpage in the holder body upon fabricating the holder body as used in the present specification.
The invention of claim 2 as shown in
FIGS. 1 and 5
is the invention according to claim 1, and is characterized in that the holder body
23
is formed, at the outer periphery thereof, with a convex ring
26
projecting upwardly; that the holder body
23
is formed, inside the convex ring
26
, with a plurality of projections
24
a
,
24
b
having different diameters, and that the plurality of projections
24
a
,
24
b
are formed to be lower than the convex ring
26
and to become sequentially lower from the outermost projection
24
a
toward inner ones whereas the outermost projection
24
a
is the highest among them.
According to the wafer holder as recited in claim 2, when the wafer
22
having a larger diameter is placed on the holder body
23
, this wafer
22
contacts with the upper surface of the outermost projection
24
a
, and the horizontal displacement of the outer peripheral surface of the wafer
22
is obstructed by the inner peripheral s
Arai Katsuo
Kawahara Fumitomo
Kawamura Yasuhiko
Nakai Tetsuya
Saito Makoto
Mitsubishi Materials Silicon Corporation
Reed Smith LLP
Wilson Gregory
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