Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Reexamination Certificate
1999-11-26
2002-07-16
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
C134S001000, C134S001300, C134S002000, C134S003000, C134S027000, C134S028000, C134S029000
Reexamination Certificate
active
06419757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sintered silicon carbide which can be applied to various parts of semiconductors and to electronic parts. More particularly, the present invention relates to a sintered silicon carbide which has a high purity, a high density and to whose surface and vicinity thereof only small amounts of organic contaminants, metal element contaminants and particle contaminants attach, and which can be used for dummy wafers, targets, heating elements and the like. The present invention also relates to a method for removing organic contaminants, metal element contaminants and particle contaminants from a sintered silicon carbide which is used for dummy wafers, targets, heating elements, which is parts of semiconductors or electronic parts, and which is required to have a high density and a high purity.
2. Description of the Related Art
Silicon carbide, particularly sintered silicon carbide, is a strongly covalently bonded compound and has heretofore been used in various fields by taking advantage of excellent properties such as excellent strength at high temperatures, heat resistance, wear resistance, chemical resistance and the like. These advantageous properties have attracted attention, and recently expectations have been placed on application in the fields of electronics, information and semiconductors.
As the degree of integration in semiconductor integrated circuits using silicon substrate increases and the line width of the circuits becomes smaller, various parts of semiconductors and electronic parts used in those fields are required to have a higher purity and a higher density. Therefore, methods of hot press sintering using nonmetallic auxiliary sintering agents and methods of reaction sintering have been intensively researched. However, the surface and the vicinity of the surface of sintered silicon carbide obtained in accordance with these sintering methods become contaminated during processes before, during and after the sintering such as sintering, working and handling, although the sintered silicon carbide has a high purity and a high density.
Therefore, to apply a sintered silicon carbide to various parts of semiconductors and electronic parts, i.e., to prevent contaminations of surfaces including particle, it is essential that the surface be cleaned and a purity of the surface as high as that of silicon wafers be achieved. However, no sintered silicon carbide having a satisfactory purity on the surface have actually been obtained.
Disclosed methods of cleaning a sintered silicon carbide are as follows: (1) a sintered silicon carbide is cleaned with an acid, treated by oxidation at 1,200° C. or higher and is thereafter surface-treated in an atmosphere of nitrogen; (2) in a method disclosed in Japanese Patent Application Laid-Open (JP-A) No. 5-17229, a sintered silicon carbide is cleaned by blasting with a silica abrasive grain and is then cleaned in a wet condition with a mixed acid containing hydrofluoric acid and nitric acid; (3) in a method disclosed in JP-A No. 6-77310, a sintered silicon carbide is cleaned by dipping into an aqueous solution of hydrofluoric acid, rinsed with ultrapure water, cleaned with oxygen and a halogen gas in a dry condition and is then treated with oxygen; and (4) in methods disclosed in JP-A Nos. 55-158622, 60-138913 and 64-72964, porous silicon carbide is cleaned with a gas of a hydrogen halide and an inorganic acid to increase the purity and then the purified silicon carbide is subjected to secondary sintering because purification to a high degree is very difficult after the sintering has been conducted.
The above methods have a drawback in that additional treatments such as oxidation, blast cleaning and secondary sintering is required in addition to simple cleaning in the wet condition and therefore the processes become complicated. These methods cannot be considered to be satisfactory as cleaning methods.
SUMMARY OF THE INVENTION
The present invention is based on the above circumstances and an object of the present invention is to provide a sintered silicon carbide having a high density and containing only small amounts of organic and inorganic impurities on the surface and in the vicinity of the surface.
Another object of the present invention is to provide a method for easily cleaning a sintered silicon carbide in a wet condition to remove organic and inorganic impurities present on the surface and in the vicinity of the surface of the sintered silicon carbide so that the sintered silicon carbide can be applied to various parts of semiconductors and electronic parts.
In the intensive research carried out by the present inventors to achieve the above objects, the present inventors focused their attention on the fact that, even when a sintered silicon carbide having a high density and a high purity which can be applied to various parts of semiconductors and electronic parts is obtained, the concentrations of organic and inorganic impurities on the surface and in oxide layers increase by contamination of the obtained sintered silicon carbide in succeeding steps, and the present invention was achieved thereby.
In the first aspect of the present invention, a sintered silicon carbide having a total amount of impurity present on a surface and in a vicinity of the surface of the sintered silicon carbide less than 1.0×10
11
atoms/cm
2
and a density greater than 2.9 g/cm
2
, is provided.
In a second aspect of the present invention, a sintered silicon carbide having a total amount of impurity present on a surface and in a vicinity of the surface of the sintered silicon carbide less than 1.0×10
11
atoms/cm
2
and a density greater than 2.9 g/cm
2
, formed by a process comprising the steps of: sintering in which a mixture of silicon carbide powder and a nonmetallic auxiliary sintering agent is hot pressed at a temperature of 2,000 to 2,400° C. and at a pressure of 300 to 700 kgf/cm
2
in a nonoxidizing atmosphere; and a step of cleaning in which the sintered silicon carbide obtained after the step of sintering is cleaned in a wet condition, is provided.
In a third aspect of the present invention, a method for cleaning a sintered silicon carbide in a wet condition, comprising the steps of: dipping the sintered silicon carbide into a quasi-aqueous organic solvent; and then dipping the sintered silicon carbide into an aqueous solution of an inorganic acid; and thereafter dipping the sintered silicon carbide into pure water, is provided.
In a fourth aspect of the present invention, a method for cleaning a sintered silicon carbide in a wet condition, comprising the steps of: dipping the sintered silicon carbide into a quasi-aqueous aqueous organic solvent; and then dipping into an aqueous solution of an ammonium compound; followed by dipping the sintered silicon carbide into an aqueous solution of an inorganic acid; and thereafter dipping into pure water, is provided.
In a fifth aspect of the present invention, a method for cleaning a sintered silicon carbide in a wet condition, comprising the steps of: dipping the sintered silicon carbide into a quasi-aqueous organic solvent; and then dipping the sintered silicon carbide into an aqueous solution of an inorganic acid; followed by dipping the sintered silicon carbide into an aqueous solution of an ammonium compound; and thereafter dipping the sintered silicon carbide into pure water, is provided.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a sintered silicon carbide of the present invention, a total amount of an impurity present on a surface and in the vicinity of the surface (occasionally referred to as the surface cleanliness, hereinafter) is less than 1.0×10
11
atoms/cm
2
, preferably less than 5.0×10
10
atoms/cm
2
and more preferably less than 1.0×10
10
atoms/cm
2
. When the amount of an impurity exceeds 1.0×10
11
atoms/cm
2
, contamination such as contamination, particle and the like take place due to impurities present on the surface and in the vicinity of the surface. In th
Otsuki Masashi
Wada Hiroaki
Bridgestone Corporation
Markoff Alexander
Oliff & Berridg,e PLC
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