JPH10265277A - Porous silicon carbide sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the transfer of impurities to the open pores in a porous SiC sintered compact at the time of mechanical working and to obtain a high purity sintered compact excellent in working precision by impregnating a specified filling material into the porous SiC sintered compact obtd. by sintering SiC powder, solidifying the material to block the open pores, mechanically working the sintered compact and removing the solidified material. SOLUTION: One or more kinds of materials selected from among wax such as paraffin wax, an org. polymer such as PE, water, oil, fat, vaseline and a gelatinizer such as agar are impregnated in the form of a liq., melt, dispersion or soln. into a porous SiC sintered compact preferably having 10-60% porosity. The materials are then solidified to block the open pores in the sintered compact, the sintered compact is mechanically worked and the solidified materials are removed. It is preferable that pure water is impregnated into the sintered compact and frozen and the sintered compact with open pores blocked by ice is mechanically worked with a freeze working machine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous silicon carbide sintered body and a method for manufacturing the same, and more particularly, to a porous silicon carbide sintered body having high purity and excellent dimensional accuracy, which can be used in a semiconductor manufacturing process or the like. Related to techniques for providing the body. Further, the present invention relates to a technique for providing a porous silicon carbide sintered body that can be used for a jig for a semiconductor or the like that requires heat resistance and bending strength.

[0002]

2. Description of the Related Art A jig made of high-purity silicon carbide used in a semiconductor manufacturing process usually sinters silicon carbide powder and impregnates porous silicon carbide with metallic silicon to fill open pores. Later, it is manufactured by processing. Since the jig thus completed contains metallic silicon, it cannot be used at a temperature higher than the melting point of metallic silicon.

A member manufactured by processing a porous body made of silicon carbide, which is not impregnated with metallic silicon, is, for example, a ceramic filter. However, such a member has low purity, and technical improvement is necessary to obtain a high-purity porous body that can be used in a semiconductor process or the like.

Japanese Patent Application Laid-Open No. Hei 6-340479 discloses a method for producing a silicon carbide substrate for a jig for producing semiconductors. In this method, first, the average particle size is 1 μm to 500 μm.
m and an impurity content of 20 ppm or less, a molded body is prepared using the silicon carbide powder, and the molded body is fired under an inert atmosphere and at a temperature of 1500 ° C. to 2000 ° C. to form a porous body. Obtain a sintered body. After machining the obtained porous sintered body, a thickness of 10 μm to 5
A 00 μm high-purity silicon carbide thin film is formed on the surface of the sintered body. The impurity content of the high-purity silicon carbide thin film formed on the surface is set to 1 ppm or less. However, the impurity content of the porous sintered body obtained in the example of the publication is 5 ppm, which cannot be said to be sufficiently low in a semiconductor manufacturing process that requires higher purity. .

In the technique disclosed in Japanese Patent Application Laid-Open No. Hei 6-340479, after a porous sintered body obtained after a firing step is machined, a silicon carbide thin film is formed on the surface thereof. Other examples of forming a silicon carbide thin film on a porous silicon carbide body include JP-A-64-42365 and JP-A-5-94957. If the obtained porous silicon carbide sintered body is processed as it is, a grinding fluid or the like enters into the porous body through the open pores, and even the initially high-purity sintered body is contaminated with impurities inside.
It is very difficult to remove such impurities by washing. Even if the surface of the sintered body contaminated with impurities is coated with silicon carbide by a CVD method or the like, the purity of the coating is reduced due to impurities generated from the porous body.

A method for producing porous silicon carbide of high purity by impregnating porous silicon carbide obtained by the firing step with metallic silicon to close open pores, processing the impregnated pores, and dissolving the impregnated silicon with an acid. Is also conceivable. However, this method is too costly.

[0007]

As described above, in the prior art, the purity of a porous silicon carbide sintered body obtained after machining is relatively low. Further, even if washing is sufficiently performed after machining, it is very difficult to remove impurities that have entered the porous body. Although a sintered body can be used as it is without processing, it is difficult to produce a highly accurate one by such a method.

An object of the present invention is to obtain a porous silicon carbide sintered body having high purity and excellent processing accuracy.

[0009]

The inventor of the present invention has conducted studies on how effectively and effectively preventing contamination due to impurities during machining, and found that the pores of the silicon carbide sintered body to be machined are reduced. With a relatively high-purity material that can be easily removed in a later step, perform machining while suppressing the transfer of impurities to the open pores, and then remove the material that has closed the open pores. As a result, it was found that a porous body machined with high purity could be obtained, and the present invention was completed.

[0010] The present invention provides a method for producing a machined porous silicon carbide sintered body. This method comprises the steps of sintering silicon carbide powder and having a porous silicon carbide sintered body having open pores. Impregnating a liquid, melt, dispersion or solution of at least one material selected from the group consisting of wax, organic polymer, water, oil, petrolatum and gelling agent, and then solidifying; Machining a porous silicon carbide sintered body in which the open pores are closed by the performed, and removing the solidified from the machined porous silicon carbide sintered body. It is characterized by the following.

In the production method of the present invention, pure water can be preferably used as a material for impregnating the porous silicon carbide sintered body having open pores. When using pure water, a porous silicon carbide sintered body having open pores is impregnated with pure water and then frozen. In this way, the porous silicon carbide sintered body whose open pores are closed by the ice can be machined by the refrigerating machine. After machining, the ice that has clogged the open pores can be easily removed.

Further, the present invention provides a porous silicon carbide sintered body having high purity even after machining. The porous silicon carbide sintered body according to the present invention has a porosity of 10% to 6%.
0% and the content of elements harmful to semiconductor production is 1%
ppm or less.

Further, the porous silicon carbide sintered body of the present invention comprises:
The surface contains 1 ppm of elements harmful to semiconductor manufacturing
It may have the following dense silicon carbide thin film.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a porous silicon carbide sintered body to be subjected to machining can be obtained by sintering silicon carbide powder by a general method. For example, according to a general method, it is possible to prepare a high-purity porous body obtained by sintering silicon carbide powder having a content of an element harmful to a semiconductor of 5 ppm or less. The porous body to be processed has continuous open pores. 10% as porous silicon carbide sintered body for machining
Those having a porosity of ６０60% are preferred. A porous body having a porosity in this range has open pores that can be easily filled with a material such as wax, an organic polymer, or water. When the porosity is 10% or less, it becomes difficult to obtain a porous body having continuous open pores. The porous body made of silicon carbide is formed by molding silicon carbide powder and subjecting the obtained molded body to 1700 in a non-oxidizing atmosphere.
It is obtained by firing at a temperature of at least ℃,
With this general method, it is difficult to obtain a porous body having a porosity of 60% or more.

In the present invention, a porous silicon carbide sintered body having open pores is provided with a wax (wax), an organic polymer,
A liquid, melt, dispersion or solution of a material selected from water, oils and fats, petrolatum, gelling agents or combinations thereof is impregnated. The material impregnated to fill the pores of the porous body is not particularly limited among these. For the impregnation, a liquid, a melt, a dispersion or a solution of these materials can be used, but the viscosity is desirably low in order to facilitate the impregnation, for example, having a low viscosity of 10 poise or less. Is preferred. The material to be impregnated into the porous body desirably has high purity. In particular, it is desirable that the content of impurities harmful to the semiconductor contained in the material to be impregnated is smaller than that in the porous body. Waxes, organic polymers, water, oils, petrolatums, or gelling agents tend to be of relatively high purity and are desirable as fillers.

The wax is turned into a melt or a liquid by heating, and this can be easily impregnated into the porous silicon carbide sintered body. After the impregnation is completed, it can be solidified by cooling. As the wax, for example, a paraffin wax obtained by separating and producing a crystalline paraffin-based hydrocarbon mixture contained in petroleum can be used. Organic polymers include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polystyrene, SMR resin,
There are resins such as acrylic resin, cellulose resin and polyester resin, and polymers such as polyethylene glycol.
These resins and polymers can be heated to, for example, a softening point or higher to form a melt, which can be impregnated into a porous body. After impregnation, it can be cooled and solidified. Water is one of the materials from which a high purity is easily obtained. Particularly, it is preferable to use pure water. By immersing the porous body in pure water contained in a container and freezing the porous body impregnated with the pure water, the open pores can be closed with ice. In addition, fats and oils, petrolatum or a gelling agent may be used as a material for filling the porous body. Oils and fats that are solid at room temperature and can be easily melted by heating can be preferably used. Synthetic fats and oils can be used in addition to natural fats and oils derived from animals and plants, but it is desirable to select those with high purity as described above. If the resin melted by heating is impregnated and solidified by cooling, the open pores can be closed by fats and oils. It is desirable to use similarly high-purity vaseline. Gelling agents include agar, gelatin and the like. These substances are soluble in hot solvents, but have the property of solidifying the solution when cooled. For example, the solution can be solidified by impregnating the porous body with the gelling agent dissolved in hot water or the like, and then cooling.

In the present invention, the porous silicon carbide sintered body whose open pores are closed by the solidified material is subjected to machining such as grinding and polishing. For machining, it is preferable to use a resin-bonded or vitrified-bonded diamond grindstone or an electrodeposited diamond grindstone.
If these grindstones are used, the amount of metal impurities adhering to the surface is reduced, and the impurities on the surface are easily removed after processing.
When the open pores of the porous body are closed with ice, it is desirable to perform machining with a refrigerating machine in order to maintain the ice.

After machining, the solidified material filled in the porous silicon carbide sintered body is removed. For example, by heating in a non-oxidizing atmosphere, the solidified substance filled in the porous body can be vaporized and removed. In addition, removal can be performed by dissolving and washing with an appropriate medium such as an organic solvent and water.

After the removal step, a cleaning step, a purification step using a halogen gas or the like may be performed as necessary. Further, the surface of the machined porous silicon carbide sintered body may be coated with high-purity and dense silicon carbide by, for example, a CVD method. The thickness of the high-purity silicon carbide coating can be, for example, 10 μm to 500 μm.

As described above, by machining a porous silicon carbide sintered body whose open pores are closed by a high-purity material, it is possible to prevent a grinding fluid or the like from entering the porous body,
Contamination due to impurities during machining can be effectively prevented.
According to the present invention, it is possible to obtain an unprecedented high-purity porous silicon carbide sintered body processed with high precision.
The porosity range can be from 10% to 60%,
The content of each element harmful to semiconductor production such as iron, nickel, chromium, copper, sodium, potassium and calcium is 1p
pm or less. Further according to the invention,
A porous silicon carbide sintered body having a content of each element harmful to semiconductor production of 0.5 ppm or less, particularly 0.1 ppm or less can be provided. When exposed to a high temperature of 1000 ° C. or more in a semiconductor manufacturing process or the like, a porous silicon carbide sintered body having a harmful element content of 0.5 ppm or less is preferable. When exposed to high temperatures, a porous silicon carbide sintered body having a harmful element content of 0.1 ppm or less is preferred. On the surface of a machined high-purity porous silicon carbide sintered body, dense silicon carbide having a content of an element harmful to semiconductor production of 1 ppm or less, preferably 0.5 ppm or less, more preferably 0.1 ppm or less By forming a thin film, airtightness is given to a material, and a material with less influence of impurities can be provided. Less than,
The present invention will be described in more detail with reference to examples.

[0021]

【Example】

Example 1 A peptizer, a binder, and water were added to a commercially available high-purity silicon carbide powder having a content of each element of Fe, Ni, Cr, Cu, Na, K, and Ca of less than 1 ppm. The obtained mixture was poured into a gypsum mold to obtain a molded body. After the obtained compact was fired at a temperature of 1800 ° C., purification with a halogen gas was performed to prepare a high-purity porous silicon carbide sintered body. The porosity of the obtained sintered body was 35%.

The obtained porous silicon carbide sintered body and a commercially available paraffin wax are put together in a container, and the mixture is dried under reduced pressure at 80 ° C.
Heating was performed at a temperature of ° C. to impregnate the porous body with paraffin. Upon cooling to room temperature, the paraffin wax was solidified. Take out a porous silicon carbide sintered body filled with paraffin braze, grind it with a vitrified bond diamond grindstone, diameter 100 mm, thickness 1 m
m was prepared. The completed disk was washed with hydrofluoric nitric acid and pure water to remove surface impurities. Next, the paraffin was removed at a temperature of 700 ° C. in a heating furnace under a nitrogen atmosphere.

The disk of a porous silicon carbide sintered body having a porosity of 35% thus processed is placed in a diffusion furnace in a state of being in contact with an n-type silicon wafer, and heat-treated at 1200 ° C. for 2 hours. Was. After the heat treatment, the lifetime of the silicon wafer was measured. The lifetime was relatively long at 873 μs, and it was found that the influence of impurities from the disk of the porous silicon carbide sintered body to the silicon wafer was small. As a result of neutron activation analysis, impurities harmful to the semiconductor contained in the disc of the porous silicon carbide sintered body were 0.1 ppm or less as shown in Table 1.

Example 2 A porous silicon carbide sintered body having a porosity of 35% prepared in the same manner as in Example 1 was immersed in pure water in a container while air remaining inside the porous body under reduced pressure. Kicked out. After the porous body impregnated with pure water is frozen and ice is formed in the open pores, the porous body filled with ice is taken out and ground with a diamond grindstone of vitrified bond by a freezing processing machine to have a diameter of 100 mm. A disk having a thickness of 1 mm was produced. The resulting disc was thawed in pure water and washed with hydrofluoric nitric acid and pure water to remove impurities on the surface. Through the above steps, a disk of a machined porous silicon carbide sintered body having a porosity of 35% was obtained.

The disk of the obtained porous silicon carbide sintered body was evaluated in the same manner as in Example 1. As a result, the wafer lifetime was 956 μs. As a result of neutron activation analysis, impurities harmful to the semiconductor contained in the disk were 0.1 ppm or less as shown in Table 1.

Comparative Example 1 A porous silicon carbide sintered body having a porosity of 35%, prepared in the same manner as in Example 1, was directly subjected to grinding. Tap water was used as the grinding fluid. Grinding using a vitrified bond diamond grindstone, diameter 1
A disk having a thickness of 00 mm and a thickness of 1 mm was prepared. The completed disk was washed with hydrofluoric acid and pure water, and evaluated in the same manner as in Example 1. The wafer lifetime was 8 μs. As a result of neutron activation analysis, impurities harmful to the semiconductor contained in the disk exceeded 1 ppm.

Example 3 A disk of the porous silicon carbide sintered body prepared in Example 1 was coated with SiC to a thickness of 100 μm by CVD, and the surface was covered with a dense silicon carbide film. A disk of a silicon carbide sintered body was produced. As a result of evaluating the obtained disk in the same manner as in Example 1, the wafer lifetime was 11
As long as 20 μs, it was found that contamination of impurities from the disk to the silicon wafer was more effectively suppressed. GD
When the CVD film was analyzed by -MS, as shown in Table 2, the content of each impurity element was 10 ppb or less.

Comparative Example 2 The disk of the porous silicon carbide sintered body produced in Comparative Example 1 was coated with SiC to a thickness of 100 μm by CVD, and the disk covered with a dense silicon carbide film was used. Produced. As a result of evaluation in the same manner as in Example 1, the wafer lifetime was 349 μs. When the CVD film was analyzed by GD-MS, the purity was lower than that of Example 3.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

According to the present invention, a porous silicon carbide sintered body having the following characteristics can be obtained.

(1) Although it is a machined porous body, it has high purity. (2) Since it does not contain metallic silicon, it can be used at high temperatures and has high corrosion resistance.

(3) Since it is a porous body, it has excellent thermal shock resistance. According to the present invention, a porous silicon carbide sintered body having high purity and processed with high precision can be obtained. The obtained porous body can be used even at a temperature higher than the melting point of silicon, corrosion resistance,
Excellent in chemical resistance, thermal shock resistance, etc. The porous silicon carbide sintered body according to the present invention is used as a material for forming a jig used in a semiconductor manufacturing process such as a wafer boat, a diffusion furnace tube, and a susceptor for epitaxial growth, particularly a jig used in a step including heat treatment. Useful.

Claims (4)

[Claims] 1. A method for producing a machined porous silicon carbide sintered body, comprising: forming a porous silicon carbide sintered body having open pores obtained by sintering silicon carbide powder; , Water, oils and fats,
A step of impregnating a liquid, a melt, a dispersion or a solution of at least one material selected from the group consisting of petrolatum and a gelling agent, and then solidifying; and the solidified material closes the open pores. Machining a porous silicon carbide sintered body, and removing the solidified material from the machined porous silicon carbide sintered body. A method for producing a silicon sintered body. 2. The porous material, wherein said material is pure water, said porous silicon carbide sintered body having said open pores is impregnated with said pure water and frozen, and then said open pores are closed by ice. The method according to claim 1, wherein the silicon carbide sintered body is machined by a refrigerating machine. 3. A porous silicon carbide sintered body having a porosity of 10% to 60% and a content of an element harmful to semiconductor production of 1 ppm or less. 4. The porous silicon carbide sintered body according to claim 3, wherein the surface has a dense silicon carbide thin film having a content of an element harmful to semiconductor production of 1 ppm or less.