Etching a substrate: processes – Nongaseous phase etching of substrate – Etching inorganic substrate
Reexamination Certificate
2001-10-15
2004-03-02
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Nongaseous phase etching of substrate
Etching inorganic substrate
C164S091000
Reexamination Certificate
active
06699401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for producing a Si—SiC member for heat treatment of semiconductor, for example, silicone monocrystal wafer and, more particularly, to a method for producing a Si—SiC member for heat treatment of semiconductor capable of reducing the contamination of the semiconductor as much as possible.
2. Description of Prior Arts
Conventionally, a Si—SiC material consisting of silicone (Si) and silicon carbide (SiC) has been used for a member for heat treatment of semiconductor, for example, a wafer boat for heat treatment of semiconductor (hereinafter referred to as wafer boat) because of its excellent compactness, purity and strength.
The recent higher integration of semiconductor devices, however, more strictly requests a higher purity for a heat-treating jig such as the wafer boat for heat treatment of semiconductor wafer, and the higher purity is requested also for the Si—SiC material forming the base material of this wafer boat.
Such conventional Si—SiC materials could not comply with the request of the higher purity with a content of Fe of 0.2 ppm or more and a total content of Ni, Cu, Na, Ca, Cr and K of 0.2 ppm or more as the metal impurity content even in case of a one called high-purity base material.
Further, in both the oxidation diffusion step of high temperature and the LP-CVD step of relatively low temperature, the diffusion of impurities from the wafer boat material to the semiconductor wafer is unavoidable.
Thus, giving attention to that a CVD-SiC film has excellent characteristics such as (1) excellent heat resistance and corrosion resistance, (2) an extremely small content of metal impurities, (3) suppressibility of diffusion of impurities such as the base material internal metals to the semiconductor wafer, and (4) excellent grinding characteristic with high compactness free from internal bubbles and high hardness, it has been taken as the measure for preventing the contamination to a semiconductor wafer W
1
, as shown in
FIG. 10
, to form a CVD-SiC film
21
on the surface
24
of the base material
23
of a wafer boat
22
to suppress the diffusion of the metal impurities contained in the base material
23
.
However, the Si—SiC base material
23
used for the conventional wafer boat
22
contains, as the metal impurity concentration, 0.2 ppm or more of Fe and 0.2 ppm or more of the total content of other metallic impurities as described above. When the base material
22
contains lots of impurities in this way, the impurities are diffusively present also on the surface
21
s
of the SiC film
21
in the formation of the CVD-SiC film, and the semiconductor wafer W
1
is consequently contaminated when placed on this wafer boat and heat-treated. This diffusion of impurities is supposedly caused by that the impurities present in the Si—SiC base material segregate at the tip of the CVD crystal during the growth thereof and move in the growing direction, although a general SiC film is higher in purity than the base material
22
with a bulk concentration of about 0.04 ppm for Fe.
Accordingly, in order to remove the segregated metal impurities, a strict washing with fluoric acid was performed in the past.
In order to solve such troubles, Japanese Patent Application Laid-Open No. 6-206718 discloses a high-temperature semiconductor processing apparatus formed, in stead of forming the CVD-SiC film on the Si—SiC base material, by use of an integrated self-standing CVD-SiC of ultra-high purity having a total metal impurity content of about 5 ppm by weight or less without using this base material.
This high-temperature semiconductor processing apparatus, however, has problems of low mechanical strength and limitation in the form of the apparatus to be manufactured because it has no base material.
Further, in cases where a nucleus for reaction is generated in the film forming process, and a crystal growth then occurs on the basis of this nucleus to generate the CVD-SiC film, projections may be formed on the surface of the CVD-SiC film although the size or number is varied depending on the synthetic condition. In order to provide the self-standing CVD-SiC, in this case, no grinding is generally performed so as to provide a strength as high as possible.
Accordingly, when a semiconductor wafer with a large diameter, for example, 8 inches or more is heated at a high temperature of 1100° C. or higher by use of the wafer boat, the problem of such projections causing a dislocation (so-called slip) in the semiconductor wafer arises.
Therefore, a method for producing a member for heat treatment of semiconductor suitable for the heat treatment of a semiconductor wafer with a large diameter, free from contamination of the semiconductor wafer, and causing no slip has been desired.
SUMMARY OF THE INVENTION
One object of this invention is to provide a method for producing a Si—SiC member for heat treatment of semiconductor, which is suitable particularly for heat treatment of a semiconductor war with a large diameter and free from contamination of the semiconductor wafer. Further, another object of this invention is to provide a method for producing a Si—SiC member for heat treatment of semiconductor, which is free from contamination of a semiconductor wafer and causing no slip.
The method according to this invention comprises the first step of kneading a SiC powder having a total metal impurity quantity of 0.2 ppm or less with a molding assistant; the second step of molding a compact from the kneaded raw material; the third step of calcining the compact; the fourth step of purifying the calcined body; and the fifth step of impregnating the purified body with silicon within a sealed vessel provided in a heating furnace body.
It preferably further comprises the sixth step of machining the part to make contact with a semiconductor to be heat-treated into a surface roughness Ra (JIS B0601-1982) of 0.2 &mgr;m or less.
In this invention, the first to fifth steps or the first to sixth steps are more preferably performed in this numerical order.
More preferably, the sealed vessel is formed of a porous carbon material having a porosity of 7-20%. The heating furnace body is provided with a mechanism for introducing and discharging an inert gas. The purifying step is performed by a heat treatment at a temperature of 1900-2000° C. in halogen-containing atmosphere. The machining process is performed by use of a diamond blade. A CVD-SiC film forming step is performed after the machining step. A wet acid washing is performed after the CVD-SiC film forming step. A heat treatment is performed in high-temperature oxidative atmosphere after the wet acid washing step to form a silicon oxide film on the surface, and the silicon oxide film is thereafter removed by wet acid washing.
This invention is further described from another point of view.
As the purity of the SiC powder, the total metal impurity quantity is 0.2 ppm or less. When a quantity exceeding 0.2 ppm is present in the raw material stage, the ultra-high purification particularly to the inner part of the Si—SiC member is difficult even if the purifying treatment after kneading or each treatment step in a contamination-preventing environment is performed.
As the sealed vessel, a vessel having no through-pore at least in the thickness direction of the material constituting it is preferably used. Particularly, a vessel having a lid structure for taking in and out the purified body of the SiC member (in other words, having a fitting part) is preferred.
The reason of using the porous carbon material is as follows. When the purified body of the SiC member and the impregnating silicon are arranged within the sealed vessel, and a heating impregnation is performed at 1460° C. or higher, the impurities left, even if slight, in the purified body are evaporated therefrom. In order to prevent the vapor from being stayed within the sealed vessel, the porous material is preferred. Further, as the material having a uniform pore distribution over the whole vessel to allow the evapor
Horiuchi Yushi
Kuroi Shigeaki
Culbert Roberts
Foley & Lardner
Mills Gregory
Toshiba Ceramics Co. Ltd.
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