Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Reexamination Certificate
1998-11-30
2001-07-10
Marcantoni, Paul (Department: 1755)
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
C501S091000
Reexamination Certificate
active
06258741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a corrosion-resistant member used in a region in which a gas or a plasma of a halogen-containing compound is used in a process for producing semiconductors, especially a member used as jigs such as a supporter for supporting a material to be treated, or as an inner wall member in an apparatus for producing semiconductors, which has a high corrosion resistance to a fluorine type or a chlorine type corrosive gas, or a fluorine type or a chlorine type plasma.
2. Prior Art
A process used in the production of highly integrated circuit elements such as semiconductor elements, including a dry process and a plasma process utilizing a plasma such as plasma coating, has been rapidly advanced in recent years. As the plasma process in the production of semiconductors, a halogen-type corrosive gas such as the fluorine type has been utilized in vapor deposition, etching or cleaning because of its high reactivity.
Members to be contacted with corrosive gases are required to have high corrosion resistance. As members to be contacted with the plasma in addition to the material to be treated generally include materials containing SiO
2
as a main component such as glass or quartz, or metals such as stainless steel or Monel.
In the production of semiconductors, as susceptor for holding and fixing a wafer, an alumina fired product, sapphire, a sintered product of AlN, and surface coated products of the above products by the CVD method are used because they have an excellent corrosion resistance. Furthermore, heaters obtained by coating graphite and boron nitride are used.
However, glass and quartz used heretofore have insufficient corrosion resistance and are consumed violently, and when they contact a gas or a plasma of a halogen compound, especially a fluorine or chlorine plasma, the contacting surface is etched, and the surface properties will change. Therefore, production conditions for the semiconductor, and especially etching conditions will be affected. Since a member using a metal such as stainless steel has insufficient corrosion resistance, corrosion causes the occurrence of poor products especially in the production of semiconductors.
Although sintered products of alumina and AlN have excellent corrosion resistance to fluorine-type gases as compared with the above materials, when they contact the plasma at high temperatures, their corrosion gradually proceeds and the removal of crystal particles occurs from the surface of the sintered products, and this becomes a cause of the occurrence of particles.
The occurrence of particles, even very fine particles formed by ion bombardment or reaction in a gaseous phase, becomes a cause of inconveniences such as the deterioration of properties of an element such as disconnected metal wirings or defects of pattern, or the reduction of the yield which occur by the high integration of a semiconductor and a further cleaning of the process.
To solve this problem, the present inventors proposed to form a corrosion resistant member from a material composed of 2A and 3A elements of the periodic table as a main component which forms a halogen compound stable to the surface of the material against a fluorine or chlorine-type plasma. However, the material composed of elements of Group 2A and 3A of the periodic table as main component is stable to a fluorine or chlorine-type plasma, but has a defect that the removal of a halogen compound formed on the surface of the material or a reaction in a vapor phase causes the occurrence of particles.
SUMMARY OF THE INVENTION
The present inventors have repeated experiments on a highly corrosion resistant material which does not generate particles, and which does not contain elements that deteriorate the properties of a semiconductor, and which is resistant to a gas or plasma of a halogen compound, especially a flurine or chlorine-type corrosive gas or plasma. Since a dense boron carbide produces a reaction product having a high vapor pressure even when it reacts with a halogen compound, especially fluorine or chlorine, the reaction product is released as a gas out of the reaction system without generating particles, and moreover, since boron carbide is difficult to react with an oxygen-free halogen compound, especially a fluorine-type or chlorine-type corrosive gas or plasma, the resulting product has excellent corrosion resistance.
According to this invention, there is provided a corrosion resistant member to be used in a region in which a gas or a plasma of a halogen compound is used in a process for the production of a semiconductor, wherein at least surface to be exposed to the gas or plasma is formed from a boron carbide sintered body having a relative density of at least 96% and containing 300 ppm or below, in a total amount, of metal elements consisting of alkali metals, alkaline earth metals and transition metals.
In the above corrosion resistant member, it is preferred that the above sintered body comprises boron carbide as a main component and 0.5 to 5% by weight of silicon carbide, and in an X-ray diffraction measurement, when the peak intensity of a diffraction peak assigned to the (311) face of boron carbide is Ia and the peak intensity of a diffraction peak assigned to the (002) face of graphite Ib., the peak intensity ratio expressed by Ib/Ia is 0.01 or below.
In the present invention, there is also provided a process for producing a corrosion resistant member composed of a sintered body of boron carbide used in a region in which a gas or a plasma of a halogen compound is used in a process for producing a semiconductor, wherein the process comprises a step of molding a boron carbide having an average particle diameter of 5 &mgr;m or below and a cation impurity of not larger than 5000 ppm into a predetermined shape, a step of heat-treating the resulting molded article in vacuum at 1600 to 2100° C. under 5 Pa or below so that the total amount of alkali metals, alkaline earth metals and trasition metals becomes 300 ppm or below, and a step of making the molded product dense at a temperature of 1900 to 2250° C. by firing the molded product under the above conditions to produce a product having a relative density of at least
In the above production process, as a sintering aid a powder of a carbon source in an amount calculated as a carbon and/or a powder of silicon carbide in an amount calculated as silicon carbide in a total amount of 0.5 to 10% by weight are added to the boron carbide powder, and the resulting mixture can be molded in a predetermined shape. In this case, as the powder of the carbon source, a carbon powder and/or a powder of an organic compound convertible into carbon by heat decomposition can be used. Furthermore, as the powder of the source of silicon carbide, a powder of silicon carbide and/or a powder of an organic silicon compound convertible to silicon carbide by heat decomposition can be used. As a preferred embodiment, in the mixed powder mentioned above, the powder of the silicon carbide source can be used in an amount of 0.5 to 5% by weight calculated as silicon carbide, and the powder of the carbon source can be used in an amount of 0.5 to 5% by weight calculated as carbon. Furthermore, it is preferred that the powder of of the carbon source and the powder of silicon carbide source may have an average particle diameter of 1 &mgr;m or below.
In the above production process, to convert carbon in the powder of boron carbide mixture into SiC or boron carbide (B
4
C), namely to remove graphite, it is possible to add metal silicon powder or metallic boron powder to the boron carbide powder mixture. Specific embodiments can be cited as follows.
There is provided a process for producing a corrosion resistant member, which comprises a step of mixing 4 to 12% by weight of a powder of metallic boron having an average particle diameter of 3 &mgr;m or below and 0.5 to 5% by weight calculated as carbon or an organic compound convertible to carbon by heat decomposition with a boron carbide having an average particle
Itoh Yumiko
Kohsaka Shoji
Matsumoto Hidemi
Matsunosako Hitoshi
Nakanishi Masahito
Hogan & Hartson L.L.I
Kyocera Corporation
Marcantoni Paul
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