JP2000091171A - Wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dummy wafer that has improved durability and can be subjected to discharge machining, by forming a wafer with silicon carbide that has a degree of deformation being equal to a specific value or less and contains a specific amount of nitrogen being manufactured by the reaction sintering method. SOLUTION: In a dummy wafer, a silicon source containing a silicon compound, a carbon source containing an organic compound, and a polymerization or crosslinking catalyst are dissolved in a solvent, are dried, and then are burned in a non-oxidation atmosphere. Then, the silicon carbide powder and slurry- shaped mixed powder where organic substance or carbon powder are dissolved and dispersed are allowed to flow into a forming mold to obtain a green body after drying. The green body is dipped into a high-purity Si that is heated and melted at 1,450 deg.C-1,700 deg.C in vacuum or inert atmosphere, Si is sucked into a pore in the green body due to capillarity, Si is allowed to react with a liberated carbon in the green body to form silicon carbide, and a silicon carbide sintering body is obtained by the reaction sintering method, thus manufacturing a dummy wafer with a degree of deformation of 120% or less and a nitrogen content of 150 ppm or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the evaluation of uniformity such as furnace temperature and gas concentration in processing steps such as thermal diffusion, thermal oxidation, and vapor phase growth on silicon wafers in the manufacture of integrated circuits and the like. The present invention relates to a wafer (hereinafter, referred to as a dummy wafer) used for removing contaminants and determining various processing conditions.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process such as an LSI, a step of oxidizing a wafer surface, a step of diffusing a doping element such as phosphorus or boron into silicon, and a step of
The process of forming various coatings by VD (chemical vapor deposition) or PVD (physical vapor deposition) occupies an important position, and it is important to keep the processing conditions constant in these processes. This is an important point in improving the yield and manufacturing more highly integrated devices.

[0003] In the above process, generally, a batch process in which a boat loaded with 100 or more wafers is placed in a reactor equipped with a heater and each process is performed is adopted. There is a problem that there is a temperature difference depending on the position and the concentration of the raw material gas becomes non-uniform. For this reason, dummy wafers not used as product wafers are installed at locations where processing conditions such as temperature and concentration of source gas may be different from processing conditions at other locations in the reaction furnace, and stacked on each dummy wafer. The uniformity of the processing conditions is evaluated based on whether or not the thickness and components of the thin films are the same. The dummy wafer is also used for examining the plasma processing conditions in the etching apparatus and removing particles generated in the apparatus.
The dummy wafer used for such a purpose is repeatedly used at a high temperature, or is repeatedly treated with an acid to remove the film formed on the dummy wafer and thereby enable repeated use.

Conventionally, the same material as that of a normal product wafer, such as silicon or quartz, has been used as the material of the dummy wafer. However, in the case of a dummy wafer formed of silicon, since the heat resistance is not so good, the shape is likely to change with time, and the durability to acid is low,
There is a problem that the surface is roughened by melting and particles are easily generated, and the life as a dummy wafer is short. On the other hand, in the case of quartz, heat resistance and durability are not sufficient, and it is not conductive, so that it cannot be used for etching or the like. For this reason, instead of silicon and quartz, carbon materials with excellent heat resistance and ceramic materials with excellent heat resistance and durability are expected as materials for dummy wafers, among which the constituent elements are harmless to semiconductor devices that are products. For these reasons, sintered silicon carbide is most expected.

[0005] One of the methods for producing a silicon carbide sintered body is a reaction sintering method. In this reaction sintering method, first, a silicon carbide powder and an organic substance or a carbon powder composed of a carbon source are dissolved and dispersed in a solvent to produce a slurry-like mixed powder. Next, the obtained mixed powder is poured into a casting mold, an extrusion mold, a press mold, or the like and dried to obtain a green body. Next, the obtained green body is heated under a vacuum atmosphere or an inert gas atmosphere, immersed in molten metal silicon, and free carbon in the green body and silicon absorbed into the green body due to capillary action. To obtain a silicon carbide sintered body.

However, since the silicon carbide sintered body manufactured as described above is electrically insulating, electric discharge machining cannot be performed, and there is a limitation in machining. In particular, when manufacturing a thin film part of 1 mm or less, it is difficult to handle the green body. Therefore, usually, a green body of several mm is manufactured, a sintered body is manufactured, and then a predetermined thickness is ground by milling or the like. Processing had to be done and the economic disadvantage was great.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object of the present invention is to provide a method for manufacturing a silicon wafer by using a silicon carbide sintered body as a material for a dummy wafer. An object of the present invention is to provide a dummy wafer which has a small degree of deformation when used, has excellent durability, and can be subjected to electric discharge machining.

[0008]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that a silicon carbide sintered body containing a certain amount of nitrogen produced by a reaction sintering method has a small dimensional change of a molded body and a high performance. Purity, high density, high toughness silicon carbide sintered body, also has conductivity by containing nitrogen,
The inventors have found that electric discharge machining and the like are possible, and have further found that when the silicon carbide sintered body is used as a dummy wafer, it can exhibit extremely excellent characteristics, and have completed the present invention. That is, <1> a wafer having a degree of deformation of 120% or less, obtained by a reaction sintering method, and formed from a silicon carbide sintered body containing 150 ppm or more of nitrogen.

<2> The wafer according to <1>, wherein the number of diffusion of iron is 1 × 10 ¹² or less.

<3> The volume resistivity of the silicon carbide sintered body is
Above, wherein the at 10 ⁰ Ω · cm or less <1>
Or it is a wafer as described in <2>.

<4> The wafer according to any one of <1> to <3>, wherein the total content of the impurity elements in the silicon carbide sintered body is less than 10 ppm.

<5> The reaction sintering method comprises the steps of:
Dissolving and dispersing an organic substance comprising at least one or more nitrogen sources and an organic substance or carbon powder comprising at least one or more carbon sources in a solvent to produce a slurry-like mixed powder; Pouring the slurry-like mixed powder into a molding die and drying it to produce a green body; and subjecting the green body to a vacuum atmosphere or an inert gas atmosphere,
It is immersed in high-purity metallic silicon that has been heated to 450 to 1700 ° C. and melted, and silicon absorbed by pores in the green body by capillary action and free carbon in the green body are reacted to form silicon carbide. And a step of filling pores in the green body by a reaction sintering method. The wafer according to any one of <1> to <4>, wherein the wafer is a reaction sintering method.

<6> The reaction sintering method comprises the steps of: a silicon source containing at least one or more silicon compounds; a carbon source containing at least one or more organic compounds that generate carbon by heating; Organic matter from the source,
After dissolving the polymerization or crosslinking catalyst in a solvent and drying,
A step of producing the nitrogen-containing silicon carbide powder by calcining the obtained powder in a non-oxidizing atmosphere; a silicon carbide powder containing the nitrogen; and an organic substance or carbon comprising at least one or more carbon sources. Dissolving and dispersing the powder in a solvent to produce a slurry-like mixed powder; pouring the slurry-like mixed powder into a molding die; and drying to produce a green body; The green body is immersed in high-purity silicon melted by heating to 1450 to 1700 ° C. in a vacuum atmosphere or an inert gas atmosphere, and silicon sucked up into pores in the green body by capillary action, and silicon in the green body <1> to <4>, wherein the method comprises reacting free carbon with silicon to form silicon carbide to fill pores in the green body.
The wafer according to any one of the above.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The dummy wafer of the present invention has a degree of deformation of 120%.
In the following, the nitrogen obtained by the reaction sintering method is 150p
It is formed from a silicon carbide sintered body containing at least pm. In the dummy wafer of the present invention, the iron diffusion quantity (pieces)
It is preferable that it is 1 × 10 ¹² or less.

The dummy wafer of the present invention has a degree of deformation (%).
Is 120 or less, preferably 100 or less. A semiconductor substrate such as a silicon wafer is subjected to various processes in a heat treatment fireplace, and these processes are performed by setting the wafer substrate on a wafer board placement device. The placement device is provided with a holding groove for placing the wafer. When the dummy wafer is supported on the holding groove so that the gas introduced into the furnace does not directly hit the wafer to be processed, the deformation degree ( %)But,
If it exceeds 120, it cannot be supported by the holding groove.

In the present invention, the term "deformation degree" refers to a dummy wafer obtained by repeating a test process in which a dummy wafer is heated at a rate of 100 ° C./hour to 1250 ° C., held for 10 hours, and then cooled to room temperature by natural air cooling ten times. Of the dummy wafer before the test (the amount of undulation after the test) and the in-plane undulation of the dummy wafer before the test (the amount of the undulation before the test) and are calculated by the following equation (1). Here, the in-plane undulation amount is the highest of the first virtual cut surface assuming that the dummy wafer is cut in the width direction along a first line (radius) passing through the center of the dummy wafer. When the height difference between the portion and the lowest portion is obtained, and it is assumed that the dummy wafer is cut in the width direction similarly along a second line (radius) passing through the center of the wafer and orthogonal to the first line. When the height difference between the highest part and the lowest part of the second virtual cutting plane is obtained,
The average value of both is used.

Equation (1) Deformation degree (%) = undulation amount after test / undulation amount before test ×
100

In the dummy wafer of the present invention, the diffusion quantity (pieces) of iron is preferably 1 × 10 ¹² or less, more preferably 1 × 10 ¹¹ or less. If the iron diffusion quantity (pieces) exceeds 1 × 10 ¹² , the carrier lifetime and PN junction inversion tend to be undesirably affected.

In the present invention, the diffusion quantity (pieces) of iron means that after the surface of a silicon wafer is sandwiched between dummy wafers,
It means that the temperature was raised to 1250 ° C. at 100 ° C./hour, held for 10 hours, cooled to room temperature by natural air cooling, and then the number of atoms of iron diffused within 1 μm from the surface of the sandwiched silicon wafer was measured.

The dummy wafer of the present invention is obtained by a reaction sintering method and contains a silicon carbide sintered body containing 150 ppm or more of nitrogen (hereinafter referred to as a nitrogen-containing silicon carbide sintered body obtained by the reaction sintering method). Is formed.)

When the nitrogen-containing silicon carbide sintered body obtained by the above reaction sintering method contains nitrogen in a solid solution state of 150 ppm or more, the barrier of the space charge layer generated at the grain boundary is about 0.
Since it is 15 eV or less, it is estimated that good conductivity is achieved. At this time, the volume resistivity of the silicon carbide sintered body is
Shows the following 10 ⁰ Ω · cm. Therefore, in order to achieve preferable conductivity, the content of nitrogen in the sintered body should be 150 p.
pm or more, preferably 200 ppm or more. From the viewpoint of stability, nitrogen is preferably contained in a solid solution state.

The nitrogen-containing silicon carbide sintered body obtained by the reaction sintering method preferably has a total content of impurity elements of 1
Although it is less than 0 ppm, more preferably less than 5 ppm, the impurity content by chemical analysis has only a meaning as a reference value. Practically, the evaluation differs depending on whether the impurities are uniformly distributed or locally unevenly distributed. Therefore, those skilled in the art generally evaluate the extent to which impurities contaminate the silicon carbide sintered body under predetermined heating conditions by using various practical devices. Here, the impurity elements are Si, O,
Shows elements other than N and C.

The nitrogen-containing carbon carbide obtained by the reaction sintering method
The iodine sintered body has a density of 2.9 g / cm. ^ThreeHaving the above
Is preferred. 2.9 g / cm^ThreeHaving a density higher than
Not only tends to develop conductivity, but also
Stable for a long time without generating dust such as particles
Can be used.

The preferable physical properties of the nitrogen-containing silicon carbide sintered body obtained by the reaction sintering method will be examined. The silicon carbide sintered body has, for example, a bending strength at room temperature of 240.
The bending strength at 1500 to 600 MPa is 55.
0 to 80.0 MPa, Young's modulus is 2.0 × 10 ⁵ to 4.
0 × 10 ⁵ MPa, Vickers hardness 1.2 × 10 ⁵ M
Pa or more, Poisson's ratio is 0.14 to 0.21, coefficient of thermal expansion is 3.8 × 10 ^{-6 to} 4.5 × 10 ^-6 (° C. ^-1 ), thermal conductivity is 100 W / m · k or more, Specific heat is 0.15 to 0.18
cal / g · ° C., and the thermal shock resistance is preferably 400 to 600 ΔT ° C.

The dummy wafer of the present invention is formed from a nitrogen-containing silicon carbide sintered body obtained by a reaction sintering method.
The preferred reaction sintering method will be described in detail below.

The reaction sintering method includes a step of producing a silicon carbide powder, a step of producing a slurry-like mixed powder from the silicon carbide powder, and a step of producing a green body from the slurry-like mixed powder. And a step of producing a silicon carbide sintered body from the green body. In the reaction sintering method, the green body refers to a silicon carbide molded body before reaction sintering having many pores and obtained by removing a solvent from a slurry-like mixed powder. The nitrogen-containing silicon carbide sintered body obtained by the reaction sintering method is characterized by containing nitrogen, and as a method of introducing nitrogen, a step of producing silicon carbide powder, or a slurry from silicon carbide powder In the step of producing the mixed powder of the above, it is preferable to introduce by adding an organic substance comprising at least one or more nitrogen sources.

The step of producing the silicon carbide powder comprises the steps of: a silicon source containing at least one or more silicon compounds; a carbon source containing at least one or more organic compounds that generate carbon by heating; a polymerization or crosslinking catalyst; Is dissolved in a solvent, dried, and then the obtained powder is fired in a non-oxidizing atmosphere.

The step of producing a slurry-like mixed powder from the silicon carbide powder comprises dissolving and dispersing the silicon carbide powder and an organic substance or carbon powder comprising at least one or more carbon sources in a solvent. And a step of producing a slurry-like mixed powder. By sufficiently stirring and mixing in dissolving and dispersing in a solvent, pores can be uniformly dispersed in the green body in the step of producing the green body from the slurry-like mixed powder.

The step of producing a green body from the slurry-like mixed powder is a step of pouring the slurry-like mixed powder into a mold and drying it to produce a green body.

In the step of producing a silicon carbide sintered body from the green body, the green body is immersed in a high-purity silicon melted by heating to 1450 to 1700 ° C. in a vacuum atmosphere or an inert gas atmosphere, and In this step, silicon is sucked up into pores in the green body by a phenomenon, and silicon and free carbon in the green body are reacted to form silicon carbide, thereby filling the pores in the green body. By this process,
The green body is reaction-sintered to obtain a silicon carbide sintered body.

The method for introducing nitrogen will be described in more detail. In a reaction sintering method having a nitrogen introduction step,
As a method of introducing nitrogen into the silicon carbide sintered body, a method of adding an organic substance comprising at least one or more nitrogen sources simultaneously with a silicon source and a carbon source in the step of producing the silicon carbide powder, In the step of producing a slurry-like mixed powder from silicon powder, when dissolving and dispersing a silicon carbide powder and an organic substance or carbon powder comprising at least one carbon source in a solvent, at least one
There is a method of simultaneously adding, dissolving and dispersing an organic substance comprising at least one kind of nitrogen source into a solvent.

As the organic substance composed of the nitrogen source, a substance that generates nitrogen by heating is preferable. For example, a polymer compound (specifically, a polyimide resin and a nylon resin, etc.), an organic amine (specifically, , Hexamethylenetetramine, ammonia, triethylamine, etc., and their compounds and salts). Of these, hexamethylenetetramine is preferable. Also, a phenol resin synthesized using hexamine as a catalyst and containing 2.0 mmol or more of nitrogen derived from the synthesis process per 1 g of the resin can be suitably used as a nitrogen source. These organic substances comprising a nitrogen source may be used alone or in combination of two or more.

The amount of the organic substance comprising the nitrogen source is preferably at least 1 mmol per 1 g of the silicon source when the silicon source and the carbon source are simultaneously added during the process of producing the silicon carbide powder. The amount is preferably 80 μg to 1000 μg with respect to 1 g of the silicon source, and at the time of producing a slurry-like mixed powder from the silicon carbide powder, an organic substance or carbon powder comprising silicon carbide powder and at least one or more carbon sources. When added simultaneously, 0.7 mmol of nitrogen per 1 g of silicon carbide powder
Since it is preferable to contain the above, 1 g of silicon carbide powder
200 μg to 2000 μg is preferable, and
0 μg to 2000 μg is more preferred.

The process for producing the silicon carbide powder will be described in more detail. In the reaction sintering method, silicon carbide powder used as a raw material of the silicon carbide sintered body is α-type,
Examples thereof include β-type, amorphous, and mixtures thereof. In order to obtain a high-purity silicon carbide sintered body, it is preferable to use a high-purity silicon carbide powder as a raw material silicon carbide powder.

The grade of the β-type silicon carbide powder is not particularly limited, and for example, generally available β-type silicon carbide powder can be used.

The particle size of the silicon carbide powder is preferably small from the viewpoint of increasing the density.
About 10 μm, more preferably 0.05 to 5 μm
It is. If the particle size is less than 0.01 μm, handling in processing steps such as measurement and mixing tends to be difficult, and
If it exceeds 0 μm, the specific surface area is small, that is, the contact area with the adjacent powder is small, and it is difficult to increase the density, which is not preferable.

The high-purity silicon carbide powder includes, for example, a silicon source containing at least one or more silicon compounds, a carbon source containing at least one or more organic compounds that generate carbon by heating, a polymerization or crosslinking catalyst, Is dissolved in a solvent and dried, and then the obtained powder is calcined in a non-oxidizing atmosphere.

A silicon source containing the silicon compound (hereinafter referred to as “silicon compound”)
As the silicon source), a liquid source and a solid source can be used in combination, but at least one type must be selected from liquid sources. As the liquid, a polymer of alkoxysilane (mono-, di-, tri-, tetra-) and tetraalkoxysilane is used. Among alkoxysilanes, tetraalkoxysilane is suitably used, and specific examples thereof include methoxysilane, ethoxysilane, propoxysilane, butoxysilane and the like, and ethoxysilane is preferred from the viewpoint of handling. Examples of the tetraalkoxysilane polymer include a low molecular weight polymer (oligomer) having a degree of polymerization of about 2 to 15 and a liquid silicate polymer having a higher degree of polymerization. Examples of solid materials that can be used in combination with these include silicon oxide. In the above reaction sintering method, silicon oxide includes, in addition to SiO, silica sol (colloidal ultrafine silica-containing liquid, containing OH groups and alkoxyl groups inside), silicon dioxide (silica gel, fine silica, quartz powder) and the like. . These silicon sources may be used alone or in combination of two or more.

Among these silicon sources, from the viewpoint of good homogeneity and handling properties, tetraethoxysilane oligomers and mixtures of tetraethoxysilane oligomers with finely divided silica are preferred. In addition, a high-purity substance is used for these silicon sources, and the initial impurity content is preferably 20 ppm or less, more preferably 5 ppm or less.

As the carbon source containing an organic compound that produces carbon by heating (hereinafter, appropriately referred to as a carbon source), in addition to a liquid source, a liquid source and a solid source can be used in combination. Organic compounds that have a high carbon content and polymerize or crosslink by catalyst or heating, specifically, for example, monomers and prepolymers of resins such as phenolic resins, furan resins, polyimides, polyurethanes, and polyvinyl alcohol are preferable, and cellulose, Examples thereof include liquid substances such as sucrose, pitch, and tar, and a resol-type phenol resin is particularly preferable. These carbon sources may be used alone or in combination of two or more. In addition, the purity can be appropriately controlled and selected depending on the purpose. Particularly, when high-purity silicon carbide powder is required, 5 ppm of each metal is used.
It is desirable to use an organic compound that does not contain the above.

The polymerization and crosslinking catalyst used in the production of high-purity silicon carbide powder can be appropriately selected according to the carbon source. When the carbon source is a phenol resin or a furan resin, toluene sulfonic acid, toluene carboxylic acid, acetic acid Oxalic acid, sulfuric acid and the like. Among these, toluenesulfonic acid is preferably used.

The ratio of carbon to silicon (hereinafter abbreviated as C / Si ratio) in the step of producing a high-purity silicon carbide powder, which is a raw material powder used in the above-mentioned reaction sintering method, is determined at 1000 ° C. It is defined by performing elemental analysis on a carbide intermediate obtained by carbonization. Stoichiometrically, C /
When the Si ratio is 3.0, the free carbon in the generated silicon carbide is 0
%, But actually, the SiO
Free gas is generated at a low C / Si ratio due to gas volatilization. It is important to determine the composition in advance so that the amount of free carbon in the produced silicon carbide powder does not become an unsuitable amount for the production use of a sintered body or the like. Normally, 16
In the case of sintering at 00 ° C. or more, the C / Si ratio is 2.0 to 2.5.
When it is set, free carbon can be suppressed, and this range can be suitably used. When the C / Si ratio is 2.5 or more, the amount of free carbon increases remarkably. However, since this free carbon has an effect of suppressing grain growth, it may be appropriately selected according to the purpose of forming particles. However, when the atmosphere is fired at a low or high pressure, C to obtain pure silicon carbide is used.
Since the / Si ratio fluctuates, in this case, the C /
It is not limited to the range of the Si ratio.

In the reaction sintering method, a silicon source and a carbon source containing an organic compound which generates carbon by heating are dissolved in a solvent and dried to obtain a powder. The mixture with the carbon source is cured to form a powder, if necessary. As a curing method,
Examples thereof include a method of crosslinking by heating, a method of curing with a curing catalyst, and a method of electron beam or radiation. The curing catalyst can be appropriately selected according to the carbon source, but in the case of a phenol resin or a furan resin, toluene sulfonic acid,
Acids such as toluenecarboxylic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, and maleic acid, and amines such as hexamine are used. These mixed catalysts are dissolved or dispersed in a solvent and mixed. Examples of the solvent include lower alcohols (for example, ethyl alcohol and the like), ethyl ether, acetone and the like.

A silicon source and a carbon source containing an organic compound which generates carbon by heating are dissolved in a solvent, and the dried powder is heated and carbonized. This is performed at 800 ° C. to 1000 ° C. for 30 minutes to 12 minutes in a non-oxidizing atmosphere such as nitrogen or argon.
This is done by heating the powder for 0 minutes.

Further, the carbide is heated at 1350 ° C. to 2000 ° C. in a non-oxidizing atmosphere such as argon to produce silicon carbide. The firing temperature and time can be appropriately selected according to the desired properties such as the particle size, but firing at 1600 ° C. to 1900 ° C. is desirable for more efficient production.

When a silicon carbide powder having a higher purity is required, impurities can be further removed by performing a heat treatment at 2000 to 2100 ° C. for 5 to 20 minutes during the above-mentioned firing.

As described above, as a method of obtaining a silicon carbide powder of particularly high purity, Japanese Patent Application Laid-Open No.
No.-48605, a method for producing a raw material powder as described in the method for producing a single crystal, that is, high purity tetraalkoxysilane, at least one selected from tetraalkoxysilane polymers is used as a silicon source, and carbon is generated by heating. Using a high-purity organic compound as a carbon source, a mixture obtained by homogeneously mixing these is heated and fired in a non-oxidizing atmosphere to obtain a silicon carbide powder, and a silicon carbide powder obtained, A post-treatment step of holding at a temperature of 1700 ° C. or more and less than 2000 ° C., and performing at least one heat treatment at a temperature of 2000 ° C. to 2100 ° C. for 5 to 20 minutes while maintaining the temperature; To obtain a silicon carbide powder having a content of each impurity element of 0.5 ppm or less, producing a high-purity silicon carbide powder. It is possible to use the law and the like. Since the silicon carbide powder thus obtained is not uniform in size, it is processed by pulverization and classification so as to conform to the particle size.

When nitrogen is introduced in the step of producing silicon carbide powder, first, a silicon source, a carbon source, an organic substance comprising a nitrogen source, and a polymerization or crosslinking catalyst are mixed homogeneously. As described above, when a carbon source such as a phenol resin, an organic substance including a nitrogen source such as hexamethylenetetramine, and a polymerization or crosslinking catalyst such as toluenesulfonic acid are dissolved in a solvent such as ethanol, an oligomer of tetraethoxysilane is used. It is preferable to mix well with a silicon source such as

The step of producing a slurry-like mixed powder from silicon carbide powder will be described in more detail. The step of producing a slurry-like mixed powder from silicon carbide powder,
Silicon carbide powder and an organic substance or carbon powder comprising at least one or more carbon sources are dissolved or dispersed in a solvent to produce a slurry-like mixed powder. By sufficiently stirring and mixing, the pores can be uniformly dispersed in the green body.

In the step of producing the slurry-like mixed powder from the silicon carbide powder, the organic substance comprising a carbon source used together with the silicon carbide powder includes a substance called a carbon source which generates carbon by heating. And an organic compound which generates carbon by heating. The organic substance comprising a carbon source may be used alone or in combination of two or more.

Examples of the organic compound that generates carbon by heating include coal tar pitch having a high residual carbon ratio,
Preferable examples include various sugars such as pitch tar, phenolic resin, furan resin, epoxy resin, monosaccharides such as phenoxy resin and glucose, oligosaccharides such as sucrose, cellulose, polysaccharides such as starch, and the like. Are preferred. These are preferably those that are liquid at room temperature, those that dissolve in a solvent, those that are softened by heating such as thermoplastic or heat-meltable, or those that become liquid, for the purpose of being homogeneously mixed with silicon carbide powder. Among them, a phenol resin having high strength of the obtained molded body, particularly a resol-type phenol resin is preferable.

In the step of producing the slurry-like mixed powder from the silicon carbide powder, the carbon powder used together with the silicon carbide powder includes pyrolytic carbon such as carbon black and acetylene black, graphite, activated carbon, and water-dispersible carbon. Carbon is mentioned, and preferably, those having conductivity are selected. Among these, carbon black imparted with conductivity is particularly preferred.

In the step of producing a slurry-like mixed powder from the silicon carbide powder, the silicon carbide powder and an organic substance or carbon powder comprising a carbon source are dissolved and dispersed in a solvent to form a slurry-like mixed powder. Although the solvent may be water, for example, for a phenol resin which is an organic compound that generates carbon by suitable heating, lower alcohols such as ethyl alcohol and ethyl ether,
Acetone and the like can be mentioned. In addition, it is preferable that the organic substance, the carbon powder, and the solvent composed of the carbon source have low impurity contents.

In the step of producing a slurry-like mixed powder from silicon carbide powder, an organic binder may be added. Examples of the organic binder include a deflocculant and a powdery pressure-sensitive adhesive. As the deflocculant, a nitrogen-based compound is preferable in terms of further increasing the effect of imparting conductivity, for example, ammonia and ammonium polyacrylate. Etc. are preferably used. As the powdery adhesive, polyvinyl alcohol, urethane resin (for example, water-soluble polyurethane) and the like are preferably used. In addition, an antifoaming agent may be added. Examples of the antifoaming agent include a silicone antifoaming agent.

The amount of the organic substance composed of a carbon source mixed with the silicon carbide powder is 10% to 50% as the amount of carbon.
Is more preferable, and more preferably 15% to 40%.
When the content is less than 10%, when silicon is infiltrated and converted into SiC in a process of manufacturing a silicon carbide sintered body from a green body, carbon is insufficient, and Si which cannot be deposited in the reaction contains 5% in the pores.
% Or more, it becomes difficult to obtain conductivity. On the other hand, if it exceeds 50%, the thixotropy of the slurry tends to be large, the moldability tends to be poor, and this may not be practically performed.

When nitrogen is introduced in the step of producing a slurry-like mixed powder from silicon carbide powder, first, silicon carbide powder, an organic substance or carbon powder comprising a carbon source, an organic substance comprising a nitrogen source, Is mixed homogeneously,
As described above, carbon black, an organic substance or a carbon powder composed of a carbon source such as a phenol resin, and an organic substance composed of a nitrogen source such as hexamethylenetetramine are dissolved and dispersed in a solvent such as water and ethyl alcohol. It is preferable to sufficiently stir and mix with the silicon carbide powder.

In the reaction sintering method, the stirring and mixing in each step can be performed by a known stirring and mixing means, for example, a mixer, a planetary ball mill or the like. Stir mixing
It is preferably performed for 10 to 30 hours, particularly for 16 to 24 hours.

The step of producing a green body from the slurry-like mixed powder will be described in more detail. In order to cast the slurry-like mixed powder into a mold, generally, casting is suitably used. The slurry-like mixed powder is poured into a molding die at the time of casting, left to stand, and then demolded.
A green body having a specified size can be obtained by removing the solvent by heating or air drying under a temperature condition of 0 to 60 ° C.

The step of producing a silicon carbide sintered body from a green body will be described in more detail. The green body manufactured through the above process is heated in a vacuum atmosphere or an inert gas atmosphere to a temperature equal to or higher than the melting point of high-purity metallic silicon,
It is immersed in high-purity metallic silicon melted by heating to 450 to 1700 ° C. When the green body is immersed in the molten metal silicone, silicon in a liquid state penetrates into pores in the green body due to a capillary phenomenon, and this silicon reacts with free carbon in the green body. By this reaction, silicon carbide is generated, and pores in the green body are filled with the generated silicon carbide. Since the reaction between silicon and free carbon occurs at about 1420 to 2000 ° C. as shown in the process for producing silicon carbide powder,
At the stage when the molten high-purity metallic silicon heated to 0 to 1700 ° C. has penetrated into the green body, the reaction with free carbon proceeds. The time for immersing the green body in the molten metal silicon is not particularly limited, and is appropriately determined depending on the size and the amount of free carbon in the green body.

High-purity metallic silicon is 1450 to 170
Melting is performed by heating to 0 ° C., preferably 1550 to 1650 ° C. If the melting temperature is lower than 1450 ° C., the viscosity of the high-purity metallic silicon increases, so that the high-purity metallic silicon does not penetrate into the green body due to the capillary phenomenon. If it exceeds 300, evaporation will be remarkable and the furnace body will be damaged.

Examples of the high-purity metal silicon include powder, granules, and bulk metal silicon, and bulk metal silicon of 2 to 5 mm is preferably used. In the present invention, high purity means that the content of impurities is less than 1 ppm.

As described above, the free carbon contained in the nitrogen-containing green body reacts with silicon, and the generated silicon carbide fills the pores in the green body, thereby providing a high-density and good electric power. Silicon carbide sintered body having characteristic characteristics is obtained.

In the reaction sintering method, as long as the heating conditions can be satisfied, there is no particular limitation on the production apparatus and the like, and a known heating furnace or reaction apparatus can be used.

The dummy wafer of the present invention can be manufactured by subjecting the nitrogen-containing silicon carbide sintered body obtained by the above reaction sintering method to processing such as electric discharge machining, polishing, and washing.

The dummy wafer of the present invention has a thickness of 0.5
The nitrogen-containing silicon carbide sintered body obtained by the reaction sintering method is subjected to electric discharge machining so that the nitrogen-containing silicon carbide sintered body has a diameter of 75 to 500 mm and a surface roughness (Ra) of 0.01 to 10 μm. It is preferable to perform processing such as polishing and cleaning.

[0066]

EXAMPLES The present invention will be specifically described below with reference to examples, but is not limited to the examples unless it exceeds the gist of the present invention. (Example 1) As silicon carbide powder, a central particle diameter of 1.1 µm
m high-purity silicon carbide powder (impurity content 5 pp manufactured according to the manufacturing method described in JP-A-9-48605).
m or less of silicon carbide: containing 1.5% by weight of silica) 85
0 g as an organic substance composed of a carbon source (“#
SL200 ") 150 g of water, in which 8.5 g of hexamethylenetetramine as an organic substance consisting of a nitrogen source and 9 g of ammonium polyacrylate as a deflocculant are dissolved.
After mixing in a ball mill for 6 hours, 30 g of water-soluble polyurethane (“Yukote” manufactured by Sanyo Chemical) as a powder adhesive and a silicone defoamer (Shin-Etsu Chemical Co., Ltd.)
("KM72A") was added and dispersed and mixed by a ball mill for further 10 minutes to produce a slurry-like mixed powder having a viscosity of 3 poise.

The slurry-like mixed powder was 100 m long.
m, cast into a plaster mold of width 50mm, thickness 5mm,
The green body having free carbon was produced by air drying (22 ° C.) for 24 hours.

Next, the green body was placed in a graphite crucible having an inner diameter of 200 mm and a height of 80 mm in an argon atmosphere under an argon atmosphere.
By immersing in a high-purity metallic silicon powder (manufactured by Kojundo Chemical Laboratory) heated to 550 ° C. and melted and held for 30 minutes, free carbon in the green body and the melt permeated into the green body by capillary action React with metallic silicon,
The generated silicon carbide filled the pores in the green body to produce the silicon carbide sintered body of Example 1.

The obtained silicon carbide sintered body was subjected to electric discharge machining and polishing to produce a dummy wafer having a diameter of 150 mm and a thickness of 1 mm.

Example 2 850 g to 800 g of silicon carbide powder and 150 g to 2 g of an organic substance comprising a carbon source
A dummy wafer of Example 2 was manufactured in the same manner as Example 1 except that the amount was changed to 00 g.

(Comparative Example 1) In Example 1, the center particle diameter obtained by the Addison method as silicon carbide powder was 2.
A dummy wafer of Comparative Example 1 was manufactured in the same manner as in Example 1 except that 5 μm silicon carbide powder was used, and hexamethylenetetramine was not added during the production of the slurry-like mixed powder.

Comparative Example 2 A commercially available high-purity graphite dummy wafer was used.

<Evaluation> With respect to the obtained dummy wafers of Examples 1 and 2 and Comparative Examples 1 and 2, the following evaluation, measurement of density and porosity by Archimedes method, three-point bending test, and volume resistivity by four-terminal method, respectively And an electric discharge machining test. Table 1 shows the results.

(Method of Measuring Density and Porosity by Archimedes Method)
Performed according to SR1634.

(Three-point bending test) The three-point bending test of the silicon carbide sintered body was performed according to JIS R1601.

(Method of Measuring Volume Resistivity by Four-Terminal Method) The volume resistivity of the silicon carbide sintered body by the four-terminal method was measured using “Lorester Ap” manufactured by Mitsubishi Chemical Corporation. The measurement conditions were as follows: pin interval 1 mm, sample size (length 60 m
m, width 15 mm, thickness 3 mm).

(Electric discharge machining test) The electric discharge machining test of the silicon carbide sintered body was performed using "FX2D" manufactured by Mitsubishi Electric Corporation.
The processing conditions were as follows: maximum peak current I _p = 53 (A),
No-load voltage V _O = 8 (V), average machining voltage V _G = 7
(V). The evaluation criteria were as follows: ○ when the silicon carbide sintered body having a diameter of 200 mm could be processed to a thickness of 2 mm without disconnection, and x when it could not be processed.

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[Table 1]

Further, with respect to the dummy wafers of Examples 1 and 2 and Comparative Examples 1 and 2, the degree of deformation (heat resistance and durability) and the quantity of iron diffusion (stain resistance) were evaluated. Each evaluation method is as follows. Table 2 shows the results.

(Deformation (Heat Resistance, Durability)) Five dummy wafers are placed on a wafer boat, and the wafer boat is mounted on a diffusion device capable of batch processing, and the internal temperature is raised to 1250 ° C. Warm this temperature to 10
After holding for a time, it was cooled to room temperature. The in-plane undulation amount of the dummy wafer after repeating this test process 10 times;
The in-plane undulation amount of the dummy wafer before the test was measured, and the degree of deformation (%) was calculated.

(Diffusion Quantity of Iron (Contamination Resistance)) Two dummy wafers are placed on a wafer boat while sandwiching silicon wafers, and then the wafer boat is mounted on a diffusion apparatus capable of batch processing, and the internal The temperature was raised to 1250 ° C., maintained at this temperature for 10 hours, and then cooled to room temperature. Then, the number of iron atoms within 1 μm from the surface of the silicon wafer held between the dummy wafers was measured.
The number of iron atoms was measured by dissolving the sample with an acid using a quadrupole ICP-MS (inductively coupled plasma mass spectrometer, manufactured by Seiko Instruments Inc.).

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[Table 2]

From Tables 1 and 2, the dummy wafers of Examples 1 and 2 were good in all the above measurements.

[0084]

According to the present invention, it is possible to provide a dummy wafer which has a small degree of deformation, is excellent in durability, and can be subjected to electric discharge machining when used in a manufacturing process of a silicon wafer.

Claims (6)

[Claims] 1. A wafer formed from a silicon carbide sintered body having a degree of deformation of 120% or less, obtained by a reaction sintering method, and containing 150 ppm or more of nitrogen. 2. The wafer according to claim 1, wherein the iron diffusion quantity is 1 × 10 ¹² or less. 3. The silicon carbide sintered body has a volume resistivity of 10
3. The resistance according to claim 1, wherein the resistance is ⁰ Ω · cm or less.
2. The wafer according to 1. 4. The silicon carbide sintered body according to claim 1, wherein the total content of impurity elements is less than 10 ppm.
4. The wafer according to any one of items 1 to 3. 5. A reaction sintering method comprising: dissolving a silicon carbide powder, an organic substance comprising at least one or more nitrogen sources, and an organic substance or carbon powder comprising at least one or more carbon sources in a solvent. Dispersing and producing a slurry-like mixed powder; pouring the slurry-like mixed powder into a molding die and drying to produce a green body; and subjecting the green body to a vacuum atmosphere or Under an inert gas atmosphere,
It is immersed in high-purity metallic silicon that has been heated to 1450 to 1700 ° C and melted, and silicon absorbed by pores in the green body due to capillary action and free carbon in the green body are reacted to produce silicon carbide. And filling the pores in the green body by a reaction sintering method comprising the steps of:
5. The wafer according to any one of 4. 6. A reaction sintering method comprising: a silicon source containing at least one or more silicon compounds;
After dissolving at least one or more carbon sources containing an organic compound that generates carbon by heating, an organic substance comprising at least one or more nitrogen sources, and a polymerization or crosslinking catalyst in a solvent and drying the resultant, Baking the obtained powder in a non-oxidizing atmosphere to produce nitrogen-containing silicon carbide powder; an organic substance or carbon powder comprising the nitrogen-containing silicon carbide powder and at least one or more carbon sources. Dissolving and dispersing in a solvent to produce a slurry-like mixed powder; pouring the slurry-like mixed powder into a molding die; and drying to produce a green body; and Body in a vacuum atmosphere or an inert gas atmosphere,
It is immersed in high-purity silicon melted by heating to 1450 to 1700 ° C., and reacts silicon sucked up into pores in the green body by capillary action with free carbon in the green body to form silicon carbide. Filling the pores in the green body by a reaction sintering method comprising:
5. The wafer according to any one of 4.