Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2000-02-09
2002-02-19
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S127000, C501S128000, C501S103000, C501S133000, C501S065000, C501S065000, C501S065000, C501S065000, C501S065000, C501S065000
Reexamination Certificate
active
06348428
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a crystalline inorganic fiber low in impurities, a molded body mainly started from such a crystalline inorganic fiber, and the production of such inorganic fiber and molded body. This invention relates, particularly, to a high-purity crystalline inorganic fiber suitable for a semiconductor manufacturing device, a molded body of the inorganic fiber, and a method for producing the inorganic fiber.
DESCRIPTION OF THE RELATED ART
Inorganic fibers generally used as furnace material include amorphous fiber and crystalline fiber. The crystalline fiber includes fibers having at least one of alumina, silica and zirconia as main component. Most of them are used as a high-temperature heat insulating material for industrial furnace and the like.
In the production of the crystalline inorganic fiber, a liquid containing the concerned metal elements is regulated together with a fiberization assistant to a highly viscous solution, discharged through a small hole, and then dried in the atmosphere to form a precursor fiber. The precursor fiber is thermally decomposed to form a calcined fiber. This calcined fiber is further thermally treated at a high temperature, whereby crystals according to the fiber composition are precipitated to form a final product.
Examples of the products of the crystalline inorganic fiber include a product consisting of the manufactured fiber as it is, for example, a flocculent bulk product; and a product consisting of the fine chip powder and molded body of the fiber, for example, a molded product such as a blanket or mat obtained by molding the fiber by dry method or a felt, paper, or board molded by wet method, a monolithic product such as a kneaded matter, and the like.
According to the recent promotion of the higher quality of industrial products in part, a high-purity material never polluting a matter to be heated has been desired even in respect to industrial furnaces.
As a conventional method for producing the high-purity inorganic fiber, it is known to use a high-purity raw material according to the required purity.
Japanese Patent Application Laid-Open No. 11-43826, for example, discloses a high-purity alumina silica crystalline inorganic fiber started from a material in which the impurities in a raw material solution are reduced by means of ion exchange or the like.
A method for making the molded body more pure is disclosed in Japanese Patent Application Laid-Open No. 10-7476. The thermal treatment electric furnace material described therein is obtained by baking a molded body started from alumina and silica powder at 1500-1800° C., and then thermally treating it in gas atmosphere containing hydrogen chloride, chlorine gas or the like for 25-50 hours.
The raw material for crystalline inorganic fiber generally contains alkali metal such as Na, alkali earth metal such as Ca, transition metal such as Fe, and Ti as impurities. The crystalline inorganic fiber produced from the raw material containing these impurities contains these impurities.
In the manufacture of a semiconductor, the process of heating a wafer at a high temperature is frequently adapted. Examples of the device used for this process include an epitaxial device, a diffusion furnace, an annealing furnace, an etching device, an ashing device, a high temperature furnace for CVD and the like.
Such a device is formed of a heating element, a heat insulating material, a soaking pipe, a wafer holding member, and an atmospheric gas feeding and exhausting system.
The materials of the members used therein are limited. The holding member directly making contact with the wafer and the soaking pipe surrounding the atmosphere are limited to quartz glass and silicon carbide except some of etching devices. This reason is that these materials can eliminate the influence of the impurities on the silicone wafer to be thermally treated without substantially having a different kind of element other than oxygen and carbon.
Beside heat insulating property, the heat insulating material requires characteristics such as heat resistance, chemical stability and electric insulating property. A ceramic heat insulating material is used from this reason. However, pollution of the wafer with this heat insulating material is strictly limited. The heat insulating material is generally considered to be a pollution source, and in order to prevent the pollution with the heat insulating material, the soaking pipe is provided between the heat insulating material and the wafer.
As the member for the semiconductor manufacturing device, particularly, quartz glass is frequently used because the quartz glass is excellent in heat resistance and thermal impact resistance with high purity and can easily provide various forms of members by glass working.
In a high-temperature furnace, the heat insulating material is hardly used in contact with or adjacent to quartz glass, because the quartz glass is likely to devitrify.
Quartz glass is a material considered to be the supercooled liquid of silica, which precipitates cristobalite crystal when a condition of crystallization is imparted. The cristobalite has a thermal expansion coefficient different from quartz glass, and the part where crystallization progressed is cracked and seen opaque. Such a phenomenon is called devitrification, which is the typical deterioration form of quartz glass. Besides the deterioration of the member, this devitrification is an undesirable phenomenon in the sense that impurities are present enough to cause the devitrification.
With respect to the devitrification (crystallization) of quartz glass, alkali metal such as Na is famous as the nuclei generating agent and grow promoter thereof. Alkali earth metal such as Ca is also a typical element devitrifying quartz glass.
On the other hand, there has been a strong demand toward the use of the heat insulating material in contact with quartz glass, because this can enhance the freedom in device design to manufacture a highly functional compact device at a low cost. Namely, a heat insulating material having a small content of alkali metal or alkali earth metal or never releasing it, even if contained, has been desired.
In the most advanced device manufacture, pollution with heavy metal such as Fe, Cu, Ni or the like is avoided. Particularly, Cu and Ni are known as elements apt to pollute with high diffusing speed in silicon or silicon oxide such as quartz glass. It is considered that the pollution sufficiently progresses when the content of such a heavy metal element contained in the thermal treatment member of the silicone wafer is 2 ppm or more.
Cu, Ni and Na easy pass through quartz glass with high diffusing speeds in quartz glass. Thus, in order to manufacture a device extremely avoiding the pollution therewith, a further countermeasure is required.
In the method disclosed in Japanese Patent Application Laid-Open No. 10-7476, which is shown as this countermeasure, the reaction area is small, a long time is required for the thermal treatment, and productivity is poor as well as the complicated working process.
In the technique of enhancing the purity shown in Japanese Patent Application Laid-Open No. 11-43826, removable elements are limited, and the degree of removal of impurity is also insufficient.
SUMMARY OF THE INVENTION
This invention has an object to provide a high-purity crystalline inorganic fiber sufficiently low in the content of impurities, a molded body consisting of such an inorganic fiber, and a method for producing such an inorganic fiber.
A preferable solving means of this invention comprises a high-purity crystalline inorganic fiber, a molded body thereof, and a method for producing the same according to Claims 1-13.
In the manufacture of a high-purity crystalline inorganic fiber or molded body thereof according to this invention, impurities are removed by a thermal treatment in gas atmosphere containing chlorine.
The method of this invention can be realized, for example, by adding the process of removing impurities by a thermal treatment in gas atmosphere c
Fujii Mikiya
Kawai Kazuhide
Misu Yasuo
Morita Keiji
Takahashi Makoto
Group Karl
Toshiba Monofrax Co., Ltd.
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