Plastic and nonmetallic article shaping or treating: processes – Carbonizing to form article – Controlling varying temperature or plural heating steps
Reexamination Certificate
2001-08-30
2004-03-02
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Carbonizing to form article
Controlling varying temperature or plural heating steps
C264S029100, C264S029600, C264S625000
Reexamination Certificate
active
06699411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silicon carbide sintered body having excellent heat resistance and of high purity, which silicon carbide sintered body is advantageously used as a component for a semiconductor manufacturing apparatus or electronic information equipment, or as a structural component of a vacuum device or the like, and also relates to a method for producing the same.
2. Description of the Related Art
Silicon carbide has conventionally been remarked as a material which can be used at high temperatures for the reason that is has excellent strength, heat resistance, thermal shock resistance, and wear resistance even at high temperatures higher than 1000° C. Recently, a sintered body of silicon carbide has been used as an alternative material of quartz used as a jig for manufacturing a semiconductor.
As a method for producing a sintered body of silicon carbide as described above, a reaction sintering process is known. In this reaction sintering process, first, silicon carbide powder and carbon powder are dissolved and dispersed in a solvent and mixed particles in a slurry form are produced. The produced mixed particles are poured into a casting mold, an extrusion mold, or a press mold, and then dried, to thereby obtain a non-sintered molded body (green body). The obtained green body is heated in a vacuum atmosphere or in an inert gas atmosphere, and thereafter is immersed in molten metal silicon so as to allow free carbon in the green body and the molten metal silicon drawn up into the green body due to capillary phenomena. Thus, a sintered body of silicon carbide is obtained.
A sintered body of silicon carbide which is used for a jig for manufacturing a semiconductor, or the like is required to have a high purity. However, under the existing circumstances, it is difficult to obtain a high purity silicon carbide sintered body.
In order to produce a high purity silicon carbide sintered body, for example, there have been proposed the following methods. One is a method in which an SiO
2
film is formed on a surface of a sintered body of silicon carbide and impurity elements are confined in the SiO
2
film, and thereafter, the SiO
2
film is dissolved and removed by using an acid such as hydrofluoric acid, to thereby obtain a high purity silicon carbide sintered body. Another is a method in which a green body is calcined at 2000° C. or thereabouts in a vacuum before it is impregnated with molten metal silicon so as to remove impurity elements, to thereby obtain a high purity silicon carbide sintered body.
However, the former method has a problem in that an oxidizing furnace dedicated for forming the SiO
2
film, and processing equipment for handling the acid are required. Further, the latter process has a problem in that the number of steps increases. On the other hand, there has also been known a method in which the surface of the silicon carbide sintered body is coated by using chemical vapor deposition (CVD). However, this method has a problem in that the number of steps increases and production costs also increase, and many impurity elements may be contained in an obtained sintered body. There is a possibility that the silicon carbide sintered bodies obtained by these methods may contain unreacted metal silicon remaining therein depending on an Si/C ratio. In this case, there arises an important problem in that the silicon carbide sintered body can merely be used only at a melting point (1420° C.) or less of the remaining metal silicon.
Accordingly, there is still further considered a method in which a slurry containing a predetermined amount of carbon powder added to and mixed with silicon carbide powder is produced for the purpose of preventing the metal silicon from remaining in the silicon carbide sintered body and controlling the Si/C ratio. However, in this case, the specific gravity of both powders and respective grain sizes are greatly different from each other, and therefore, it is difficult to produce a homogeneous slurry. Therefore, it is also considered that an amount of dispersion medium or an amount of a surface active agent is increased. However, if the amount of dispersion medium is increased, production of a green body having high density becomes difficult. If the amount of a surface active agent is increased, impurity elements resulting from the surface active agent may increase.
Accordingly, an object of the present invention is to solve the above-described various problems in the conventional methods and to provide a high purity silicon carbide sintered body having excellent heat resistance, and a method for producing the silicon carbide sintered body in a simplified manner.
SUMMARY OF THE INVENTION
The present inventors have earnestly studied and found the mechanism of producing a high purity silicon carbide sintered body by using, as a raw material, a carbon generating substance in a liquid form. The present invention has been devised in view of the aforementioned.
A method for producing a silicon carbide sintered body comprises the steps of: preparing a slurry by dispersing silicon carbide powder in a solvent; forming a molded body by pouring the slurry into a mold and effecting calcination for the slurry in a vacuum atmosphere or in an inert gas atmosphere; and sealing pores within the calcined molded body by impregnating the pores with high purity metal silicon molten by heating, and allowing the high purity metal silicon and carbon contained in the molded body to react on each other in the pores so as to produce silicon carbide.
A silicon carbide sintered body of the present invention is produced by the above-described method for producing a silicon carbide sintered body according to the present invention. In the silicon carbide sintered body of the present invention obtained by the method for producing a silicon carbide sintered body, the content of impurities such as metal is extremely low and the silicon carbide sintered body is of high purity and has a density of 2.90 g/cm
3
or more, and is further excellent in heat resistance.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A method for producing a silicon carbide sintered body according to the present invention comprises a slurry preparing step, a molded body forming step, a calcination step, and a pore sealing step. The method for producing a silicon carbide sintered body according to the present invention is referred to as a so-called reaction sintering process.
Slurry Preparing Step:
In the slurry preparing step, a slurry is prepared by dispersing is silicon carbide powder in a solvent.
Silicon Carbide Powder:
The silicon carbide powder is obtained, for example, by dissolving, in a solvent, a silicon source containing at least one kind of silicon compound, a carbon source containing at least one kind of organic compound which generates carbon upon heating, and a polymerization or cross-linking catalyst, and drying the mixture, and thereafter, firing the obtained powder in a non-oxidizing atmosphere.
The silicon carbide powder may be &agr;-type, &bgr;-type, amorphous type, or a mixture thereof. The grade of the &bgr;-type silicon carbide powder is not particularly limited and a commercially available &bgr;-type silicon carbide powder may be used. When a high purity silicon carbide sintered body is obtained in the present invention, high purity silicon carbide power is preferably used as a raw material of the sintered body.
It is preferable that the grain size of the silicon carbide powder be smaller from the standpoint of achieving high density. Specifically, the grain size is preferably in the range from 0.01 to 10 &mgr;m, and more preferably in the range from 0.05 to 5 &mgr;m.
If the grain size is smaller than 0.01&mgr;m, handling in processes such as measuring, mixing, and the like is apt to become difficult. Further, if the grain size is greater than 10 &mgr;m, the specific surface area thereof is small, namely, the contact area of adjacent particles becomes small, thereby making it difficult to achieve high density. Either case
Odaka Fumio
Takahashi Yoshitomo
Ushita Kazuhiro
Bridgestone Corporation
Fiorilla Christopher A.
Oliff & Berridg,e PLC
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