JP2004231493A - Porous silicon carbide sintered compact and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous silicon carbide sintered compact with high purity and high strength, which is sufficiently usable as a material for semiconductor manufacturing, and its manufacturing method. <P>SOLUTION: The porous silicon carbide sintered compact has a porosity of 30-50% and a pore diameter of 0.2-20 μm, and the silicon carbide particles forming the framework of the porous sintered compact have a ratio of neck diameter/particle diameter of ≥0.6. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a porous silicon carbide sintered body and a method for producing the porous silicon carbide sintered body, and more particularly, to a porous silicon carbide sintered body having high purity and high strength, and a cold isostatic pressing method. The present invention relates to a method for producing a porous silicon carbide sintered body, which is characterized by reaction sintering of a hydraulic (CIP) molded body under specific conditions and recrystallization of a slip cast molded body under specific conditions.
[0002]
[Prior art]
Silicon carbide sintered bodies, which are a type of ceramics, have excellent physical properties such as heat resistance, thermal conductivity, corrosion resistance, strength, and abrasion resistance. It is used as a heat shield plate, a furnace tube, and a support base for a wafer heat treatment apparatus, and is an important material supporting the semiconductor industry.
The silicon carbide sintered body is preferably a dense silicon carbide sintered body having a small porosity from the viewpoint of heat resistance and mechanical strength. However, in order to obtain a dense silicon carbide sintered body having a small porosity, it is necessary to incorporate a sintering aid into the molded body before firing, which remains in the silicon carbide sintered body after sintering, It is known that these adversely affect the wafer as impurities.
[0003]
As a method of solving this, there is also known a method of impregnating a porous silicon carbide sintered body manufactured without blending a sintering aid with metallic silicon and closing the pores to supplement the mechanical strength. I have.
However, since the silicon carbide sintered body impregnated with metallic silicon is chemically the same as the silicon wafer, when the silicon carbide sintered body is used as a jig for manufacturing a semiconductor, the silicon carbide sintered body is subjected to high-temperature treatment. There is an adverse effect that the jig and the wafer adhere to each other.
[0004]
Further, as a method for solving these problems, a method of forming a silicon carbide film on a porous silicon carbide sintered body and shielding impurities in the silicon carbide sintered body or the above-described metal silicon from the outside is also known. .
However, in the case where a silicon carbide film is formed on a porous silicon carbide sintered body, there is a problem that the silicon carbide film peels off due to rapid temperature rise and fall and becomes particles. That is, there is a problem that the thermal shock resistance is weak.
[0005]
Then, in order to improve such adverse effects, pores of a sintered body obtained by sintering a silicon carbide powder raw material containing at least 70% by weight of a powder having an average particle diameter of 10 μm or less as shown in Patent Document 1, It has been proposed to coat with a film of silicon carbide obtained by a gas phase method.
[0006]
[Patent Document 1]
JP-A-3-23267 (Claims, page 9, lower right column, line 9 to page 3, left column, line 15)
[0007]
[Problems to be solved by the invention]
However, there is a problem that the porous silicon carbide sintered body manufactured by the above-mentioned conventional method does not always have sufficient mechanical strength. In the case of a conventional porous silicon carbide sintered body, the bending strength is generally 10 MPa or less, and even in the case of the above-mentioned Japanese Patent Application Laid-Open No. H3-23267 (Patent Document 1), the porous carbonized The bending strength of the silicon sintered body was 21.5 MPa or less, and even when covered with a silicon carbide film, it was 78 MPa or less.
[0008]
The present invention has been made in order to solve the above technical problems, and has a sufficiently high purity as a member used in the semiconductor manufacturing industry, and a high-strength porous silicon carbide sintered body and porous silicon carbide. An object of the present invention is to provide a method for manufacturing a sintered body.
[0009]
Another object of the present invention is to provide a porous silicon carbide sintered body having a porous silicon carbide sintered body as a base material and having a silicon carbide film formed on the surface thereof and having improved thermal shock resistance and strength characteristics. And a method for producing a porous silicon carbide sintered body.
[0010]
[Means for Solving the Problems]
The present invention has been made to solve the above technical problems, and according to the present invention, a porous silicon carbide sintered body having a porosity of 30% to 50% and a pore diameter of 0.2 μm to 20 μm. A porous silicon carbide sintered body characterized in that the ratio of neck diameter / particle diameter of silicon carbide particles constituting the skeleton of the porous sintered body is 0.6 or more.
[0011]
The porous silicon carbide sintered body of the present invention uses a conventional porous silicon carbide in which the relationship between the diameter of the neck portion to which the silicon carbide particles in the sintered body are bonded and the silicon carbide particle diameter is determined by the neck diameter / particle diameter ratio. A major feature is that the structure is set to 0.6 or more, which has not been obtained with a sintered body.
[0012]
Even when the neck diameter / particle diameter ratio is 0.6 or more, when the porosity of the porous silicon carbide sintered body exceeds 50%, and when the pore diameter exceeds 20 μm, the number of neck portions tends to decrease. In some cases, sufficient strength cannot be obtained, and irregularities on the surface of the porous silicon carbide sintered body become large. For example, when the porous silicon carbide sintered body is used in a boat for a semiconductor wafer heat treatment apparatus, it causes slip of a semiconductor wafer. Therefore, it is not preferable. On the other hand, if the porosity is less than 30%, the number of necks increases and the strength is high, but the cushioning resistance against thermal shock is insufficient, which is not preferable.
Further, in order to reduce the pore diameter of the porous silicon carbide sintered body to less than 0.2 μm, it is necessary to perform sintering at a relatively low temperature, which is not preferable because sufficient strength cannot be obtained.
[0013]
The present invention provides an unprecedented high strength (bending strength of 40 MPa or more) and thermal shock resistance (ΔTc) by setting the neck diameter / particle diameter ratio, porosity, and pore diameter of the porous silicon carbide sintered body to specific ranges. Is 1200 ° C. or higher).
[0014]
In the porous silicon carbide sintered body of the present invention, the aluminum concentration in the sintered body is 0.1 to 3 ppm, and 80% or more of the aluminum concentration is present in the neck portion to which the silicon carbide particles are bonded. Is preferred. With such a configuration, the neck strength of the porous silicon carbide sintered body can be further increased.
[0015]
Here, it is desirable that the porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and coated even inside the open pores of the base material by a CVD method.
As described above, since the silicon carbide film is deposited and covered even to the inside of the open pores of the base material, the contamination to the wafer is suppressed with higher purity. Also, the mechanical strength can be increased. Further, the silicon carbide film is characterized in that it is difficult to peel off and has a high thermal shock resistance.
[0016]
In particular, it is preferable that at least the pores in the surface layer of the base material are formed as closed pores by the silicon carbide film. The silicon carbide film placed in such a state adheres tightly to the base material and is more difficult to peel off.
The porous silicon carbide sintered body on which the silicon carbide film thus formed is formed preferably has a bending strength of 180 MPa or more and a thermal shock resistance (ΔTc) of 1200 ° C. or more.
[0017]
Further, the present invention has been made to solve the above technical problems, and according to the present invention, a resin serving as a carbon source, a silicon carbide raw material powder having an average particle size of 1 to 100 μm, Is formed by cold isostatic pressing with addition of 1 to 20 μm of silicon powder, followed by reaction sintering of the compact at a temperature of 1800 to 2300 ° C. and a reduced pressure of 0.01 to 10 Torr. A method for manufacturing a silicon carbide sintered body is provided.
[0018]
When the average particle diameter of the silicon carbide raw material powder is less than 1 μm, it is difficult to adjust the pore diameter of the sintered body because a large amount of fine powder of less than 1 μm is contained, and the deformation after firing becomes large, It is not preferable because dimensional control of the product becomes difficult. If it exceeds 100 μm, it is difficult to make the ratio of neck diameter / particle diameter of the sintered body 0.6 or more, and it is not preferable because a porous silicon carbide sintered body having sufficient strength cannot be obtained. In addition, the porosity and the pore diameter increase, and the irregularities on the surface of the sintered body increase, which is not preferable as a member for a semiconductor wafer heat treatment apparatus such as a boat.
On the other hand, if the average particle diameter of the silicon powder is less than 1 μm, the dispersion of the silicon powder is poor, and a locally low strength portion is formed, which is not preferable. If it exceeds 20 μm, only this surface reacts with carbon in the binder in the calcination stage, the silicon remains in the center, and when this is sintered, the remaining silicon volatilizes to form a pore diameter exceeding 20 μm. Is not preferred.
[0019]
When the excessive reaction sintering of the molded body is less than 1800 ° C., it is difficult to make the neck diameter / particle diameter ratio 0.6 or more, and metal impurities in each raw material can be volatilized during sintering. Therefore, the sintered body cannot be made high purity, which is not preferable. If the temperature is higher than 2300 ° C., the silicon carbide itself is liable to volatilize during sintering, and the strength of the neck portion is particularly lowered, which is not preferable.
Further, if the degree of pressure reduction is less than 0.01 Torr, excessive equipment is required, industrial productivity is not suitable, and if it exceeds 10 Torr, it is difficult to make the neck diameter / particle diameter ratio 0.6 or more, and It is not preferable because it becomes difficult to obtain a sintered body having a sufficient purity.
[0020]
This manufacturing method is a remarkable feature in that the raw material mixture including the silicon carbide powder, the resin, and the silicon powder is subjected to CIP molding, and then fired under a high temperature and a vacuum to perform reaction sintering.
That is, the molded body is uniformly compressed and densified by uniform pressing using a rubber press or the like. In addition, SiC generated by a reaction between silicon powder and resin-derived carbon in the subsequent high-temperature sintering promotes interparticle fusion and strengthens the neck.
As a result, the porous sintered body obtained by the above manufacturing method has a neck diameter / particle size ratio (l / r) despite having a considerably high porosity of 30% or more and 50% or less. It is as large as 0.6 or more, and has excellent strength characteristics such as bending strength. In addition, it has open pores having an average pore diameter of relatively uniform 0.2 to 20 μm. Furthermore, since it is fired under reduced pressure at a high temperature, the metal component that has come out on the surface due to partial melting is apt to evaporate and evaporate. Is less likely to accumulate. Therefore, the obtained porous silicon carbide sintered body has high purity and can suppress wafer contamination.
[0021]
Here, it is preferable that the molded body be pre-fired at a temperature of 1400 to 1600 ° C. and a degree of reduced pressure of 1 to 50 Torr before being subjected to the reaction sintering under the reduced pressure.
As described above, before the reaction sintering under reduced pressure, the molded body may be pre-fired under reduced pressure at a temperature lower than the reaction sintering temperature, to prevent unexpected shrinkage deformation at the time of main firing, strength properties. It is preferable from the viewpoints of improvement of the purity, high purification and the like.
If the calcination temperature is lower than 1400 ° C., the silicon powder and the carbon for the binder do not sufficiently react with each other, making it difficult to obtain a sintered body having a neck diameter / particle diameter ratio of 0.6 or more. Since heat shrinkage during sintering after processing is large, dimensional control of the product becomes difficult, which is not preferable. If the temperature exceeds 1600 ° C., the strength after pre-baking becomes too high, and the uniformity is poor. Further, it is preferable that the degree of reduced pressure is 1 to 50 Torr after the volatile matter of the binder is appropriately volatilized.
It is desirable to add 1 to 3 parts by weight of aluminum to 100 parts by weight of silicon powder as a solid solution or as a separate solution. Thereby, the porous silicon carbide sintered body has an aluminum concentration of 0.1 to 3 ppm in the porous silicon carbide sintered body, and 80% or more of the aluminum concentration is present in the neck portion to which the silicon carbide particles are bonded. Can be obtained.
[0022]
In addition, it is preferable that the porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and covered to the inside of the pores of the base material by a CVD method.
As described above, the silicon carbide film can be easily deposited and covered inside the pores of the base material by the CVD method, and the silicon carbide film can be deposited and covered even inside the open pores of the base material, so that a higher purity can be obtained. And the mechanical strength can be increased. Further, the silicon carbide film is hardly peeled off, has a high thermal shock resistance, and can further suppress the contamination of the wafer.
[0023]
Furthermore, the present invention has been made in order to solve the above technical problem, and according to the present invention, comprises a silicon carbide powder raw material having an average particle diameter of 1.5 μm or less, a binder having a small amount of residual carbon, and a dispersant. After the slurry is subjected to slip cast molding, the compact is sintered at a temperature of 1500 ° C. or more and 2200 ° C. or less to recrystallize silicon carbide polycrystal grains. A manufacturing method is provided.
If the average particle size of the silicon carbide powder raw material exceeds 1.5 μm, bonding by recrystallization of silicon carbide powders is not sufficiently performed, and as a result, high strength cannot be obtained, which is not preferable.
If the sintering temperature is lower than 1500 ° C., the neck diameter / particle diameter ratio cannot be 0.6 or more, which is not preferable. If the temperature is higher than 2300 ° C., silicon carbide itself tends to volatilize during sintering. In particular, the strength of the neck portion is undesirably reduced.
In addition, according to this manufacturing method, it has open pores having an average pore diameter of 0.2 to 5 μm.
[0024]
Here, before sintering the molded body, it is preferable to perform preliminary firing at 1100 to 1500 ° C. As described above, before the reaction sintering under reduced pressure, the molded body may be pre-fired under reduced pressure at a temperature lower than the reaction sintering temperature, to prevent unexpected shrinkage deformation at the time of main firing, strength properties. It is preferable from the viewpoints of improvement of the purity, high purification and the like.
Also in this manufacturing method, it is preferable to deposit and coat the silicon carbide film to the inside of the pores of the base material by the CVD method, since the purity is higher and the mechanical strength can be increased. Further, the silicon carbide film is hard to peel off, has high thermal shock resistance, and can further suppress contamination on the wafer.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the porous silicon carbide sintered body and the method for producing the porous silicon carbide sintered body according to the present invention will be described from the method for producing the porous silicon carbide sintered body. As a method of manufacturing the porous silicon carbide sintered body, two manufacturing methods are exemplified, and each will be sequentially described.
[0026]
First, the first method for producing a porous silicon carbide sintered body is as follows: a resin and a silicon powder serving as a carbon source are added to a silicon carbide raw material powder, and subjected to cold isostatic pressing (CIP) molding; It is characterized by reaction sintering under a reduced pressure at 2300 ° C. or less.
The silicon carbide powder used as a raw material preferably has an average particle diameter of 1 to 100 μm, more preferably 10 to 80 μm.
Further, a mixture of coarse powder having an average particle diameter of about 50 to 100 μm and fine powder having an average particle diameter of about 1 to 10 μm at a mixing ratio of about 30:70 to 70:30 can also be used.
Silicon carbide powder includes α-SiC and β-SiC, both of which can be used. However, those having a small amount of metal impurities, high purity, relatively well-controlled particle size distribution, and no inclusion of coarse particles are used. Preferably, α-SiC is more preferable from this point.
[0027]
As the resin used as the carbon source, a phenol resin such as a resol type or a novolak type, an epoxy resin, an acrylic resin, or the like can be used.
As the silicon fine powder used together with the silicon carbide powder and the resin serving as a carbon source, a high-purity Si powder having an average particle diameter of usually 1 to 20 μm, preferably 5 to 10 μm is used.
In the above method, the resin as a carbon source is usually 5 to 30 parts by weight, preferably 5 to 15 parts by weight, and the silicon powder is 5 to 40 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of silicon carbide powder. Parts. The amount of the silicon powder is preferably adjusted according to the type of the resin.
[0028]
Next, the mixture having the above mixing ratio is granulated, and the granulated mixture is placed in a mold such as a rubber press (rubber mold), and is usually subjected to cold isostatic pressing under a pressure of 80 to 150 MPa at a normal temperature to about 40 ° C. A hydrostatic pressure (CIP) molding is performed to obtain a molded body.
The molded body is fired at a temperature of 1800 ° C. or higher, preferably 2000 to 2200 ° C., under a reduced pressure of 0.01 to 10 Torr, preferably 0.01 to 1 Torr, and reaction-sintered.
[0029]
In the first production method, it is particularly preferable that before the reaction sintering, the molded body is pre-fired (temporarily fired) under reduced pressure at a temperature lower than the reaction sintering temperature.
Thereby, the compact can be shrunk in advance to prevent unexpected shrinkage deformation at the time of main firing (reaction sintering). Further, it is possible to facilitate the subsequent processing, and to increase and homogenize the strength of the base material. Further, impurities such as metal components evaporate and volatilize from the surface by the firing under reduced pressure, and the purity of the obtained porous sintered body can be improved.
[0030]
The calcination is preferably performed at a temperature of 1400 to 1600 ° C. and a degree of reduced pressure of 1 to 50 Torr.
Needless to say, in the case of this manufacturing method, the volatilization of the impurity metal component is also performed at the time of main firing (reaction sintering). Therefore, the porous silicon carbide sintered body obtained by this manufacturing method will be described later. In this case, the concentration of Fe as a representative of the impurity metal is 1 ppm or less (generally about 0.01 ppm), resulting in extremely high purity.
[0031]
In this first production method, the step of subjecting the pre-fired or unfired compact to high-temperature reaction sintering under reduced pressure is extremely important. In this step, carbon and fine silicon particles derived from resin in the compact are included. As shown in FIG. 1, this promotes the bonding between silicon carbide particles 7 in a semi-molten state by sintering, and adheres itself to the bonding grain boundary to expand and strengthen neck N. To play.
For this reason, although the obtained porous sintered body has a relatively large porosity of 30 to 50%, it has a large l / r (l: neck diameter, r: particle diameter) and high strength. is there. Further, the pore size distribution has open pores having a relatively uniform pore size of 0.2 to 20 μm, which is also considered to be one of the reasons why this porous sintered body exhibits high strength.
[0032]
Next, a second method for manufacturing a porous silicon carbide sintered body will be described.
In this second production method, a slurry of a silicon carbide powder raw material having an average particle size of 1.5 μm or less, a binder and a dispersant is slip-cast molded, and then sintered at a temperature of 1500 to 2200 ° C. Is recrystallized.
It is preferable that the raw material silicon carbide powder has an average particle diameter of 1.5 μm or less, more preferably about 0.8 to 1.5 μm. When the particle size of the raw material silicon carbide is larger than 1.5 μm, the porosity of the obtained porous sintered body exceeds 50% and the bending strength is reduced, so that the object of the present invention cannot be achieved. .
[0033]
In the second production method, as a binder used together with the raw material silicon carbide particles, the residual carbon ratio is usually less than 0.5% under the firing conditions in this method. For example, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, Use hydroxyethyl cellulose, furan resin, or the like.
Examples of the dispersant include an acrylic copolymer resin, an imine resin, a styrene / maleic acid copolymer resin, an oligomer thereof, a naphthalene sulfonic acid / formalin condensate, and a surfactant.
[0034]
In the above production method, the binder is usually 1 to 10 parts by weight, preferably 2 to 5 parts by weight, and the dispersant is 0.2 to 2 parts by weight, preferably 0.5 to 100 parts by weight of silicon carbide powder. １1 part by weight.
Further, the slurry concentration is preferably from 50 to 80%, particularly preferably from 60 to 70%, as a weight fraction in terms of solid content.
As the dispersion medium, hydrocarbon solvents such as naphtha, cyclohexane, and benzene, and organic solvents such as oxygen-containing organic solvents such as alcohols, ketones, esters, and ethers can also be used. From the viewpoints of safety, safety, economy and the like, it is preferable to use an aqueous dispersion medium such as water or aqueous alcohol.
[0035]
The slurry having the above mixing ratio is cast (slip cast) under a normal pressure or under a pressure at a temperature of normal temperature to about 30 ° C. using a gypsum mold or another porous material mold. Then, after drying the obtained compact, sintering is performed at a temperature of 1500 ° C. or more, particularly preferably 1800 to 2200 ° C., to recrystallize crystal grains.
[0036]
Also in the second production method, it is particularly preferable that before the main firing, the molded body is pre-fired (temporarily fired) under a reduced pressure at a temperature lower than the firing temperature. Thereby, the compact can be shrunk in advance to prevent an unexpected shrinkage deformation at the time of main firing (reaction sintering). Further, impurities such as metal components evaporate and volatilize from the surface by the reduced pressure firing to obtain The purity of the resulting porous sintered body is improved.
This calcination is preferably performed at a temperature of 1100 to 1500 ° C. and a degree of reduced pressure of 1 to 50 Torr. The porous fired body obtained by this manufacturing method also has an extremely high purity with an Fe concentration of 1 ppm or less (generally about 0.1 ppm).
[0037]
In this second production method, fine silicon carbide particles having a relatively narrow particle size distribution are formed by slip casting, and then recrystallized and sintered.
As a result, the obtained porous sintered body has a neck diameter / particle diameter ratio (l / r) in spite of considerably high porosity, similarly to the porous sintered body of the first manufacturing method. , Pore diameters are relatively uniform, strength characteristics such as bending strength are excellent, and high purity is obtained. In addition, since the raw silicon carbide powder is fine, the pore size of the obtained porous fired body is smaller than that of the porous sintered body manufactured by the first manufacturing method, and the strength becomes stronger.
[0038]
Next, the porous silicon carbide sintered body according to the present invention will be described in detail.
The porous silicon carbide sintered body has a porosity of 30 to 50%, preferably 35 to 45%, and a pore diameter of 0.2 to 20 μm, and particularly the porous silicon carbide obtained by the first production method. The range is about 5 to 20 μm for the sintered body, and about 0.2 to 5 μm for the porous silicon carbide sintered body obtained by the second manufacturing method.
In addition, it has relatively uniform open pores with a narrow pore diameter distribution.
Further, as shown in FIG. 1, the neck diameter / particle diameter ratio (l / r) of silicon carbide crystal particles 7 constituting the skeleton of the porous sintered body is 0.6 or more, preferably 0.7 to 1 .0.
[0039]
Here, the neck diameter / particle diameter ratio (l / r) refers to the particle radius r when the silicon carbide crystal particles constituting the porous sintered body are approximated to a sphere, and the neck where these are fused by sintering. The average of the ratio of the section N to the cross-sectional diameter 1 indicates the degree of progress of sintering and serves as an indirect index such as bending strength.
Further, the porous silicon carbide sintered body according to the present invention has a bending strength (three-point bending strength) of 40 MPa or more, preferably 50 to 150 MPa, and further includes Fe, K, Na, Ca, Ni, and Cr. , Al, Cu, etc., each have a concentration of 1 ppm or less, and the total concentration of all metal impurities is 10 ppm or less.
[0040]
Next, a description will be given of a porous silicon carbide sintered body in which the above-described porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and coated on the inside of the pores of the porous sintered body by a CVD method. .
The silicon carbide film is deposited on the porous sintered body by the CVD method, for example, by introducing a silane gas containing carbon such as trichloromethylsilane gas together with a hydrogen gas or the like as a carrier gas, preferably under a reduced pressure of about 40 Torr, for 1100 hours. SiC is deposited on the porous sintered body at a temperature of about 1300 ° C.
Usually, the film is formed to a thickness of 50 to 60 μm by one treatment, and preferably, this treatment is repeated several times to form a film having a surface thickness of about 120 to 240 μm.
[0041]
In the porous silicon carbide sintered body subjected to the CVD process, the silicon carbide film formed by the CVD process penetrates to the inside of the open pores, and is deposited on the pore inner wall at a considerable depth from the surface. That is a remarkable feature.
As schematically shown in FIG. 2, the surface portion of the porous silicon carbide sintered body 3 in which the silicon carbide film 2 is formed on the base material 1 of the porous silicon carbide sintered body by the CVD process is dense silicon carbide. A silicon carbide film 2a from the interface 4 between the dense silicon carbide film 2 and the base material (porous silicon carbide sintered body) 1 toward the inside of the base material (porous silicon carbide sintered body) 1 The closed pores 5 are formed by the deposition of the silicon carbide, and further toward the inside, the open pores 6 of the porous silicon carbide sintered body itself are present.
[0042]
More specifically, referring to FIG. 4, in the case where the porous silicon carbide sintered body (R material) manufactured by the first manufacturing method is used as a base material, a silicon carbide film (120 μm) It has been confirmed that a silicon carbide film of about 0.5 μm is deposited also on the inner wall of the pores of the base material (silicon carbide crystal grain surface) at a depth of 800 μm from the interface with the material.
[0043]
The porous silicon carbide sintered body coated with the silicon carbide film by the CVD treatment has a bending strength of 180 MPa or more, preferably 200 to 300 MPa or more, and a thermal shock resistance (ΔTc) of 1200 ° C. or more.
That is, in the case of a conventional silicon carbide sintered body covered with a silicon carbide film (Patent Document 1), the bending strength can be 180 MPa or more, while it is 78 MPa or less. Further, the thermal shock resistance (ΔTc) of the silicon carbide sintered body (Patent Document 1) coated with the conventional silicon carbide film does not show any abnormality up to 500 ° C., but does not show any abnormality up to 1200 ° C.
In addition, since the entire surface is covered with a high-purity CVD-silicon carbide film, metal impurities in the sintered body can be completely trapped, and an effect of preventing contamination can be obtained.
[0044]
The porous silicon carbide sintered bodies produced by the first production method and the second production method, and the porous silicon carbide sintered bodies obtained by coating these porous silicon carbide sintered bodies with a silicon carbide film, Also has high purity, high strength, and is lighter than a dense body. Therefore, taking advantage of the inherent high-temperature resistance of silicon carbide, for example, high-temperature heat treatment of a member used in a high-temperature melting vessel such as a silicon melting crucible for manufacturing semiconductor wafers, a heat shielding plate, a heating element, a resistor, and a furnace core tube. It can be suitably used for a member, and further, a semiconductor member such as a cassette boat for wafer heat treatment and a susceptor.
[0045]
In particular, the porous silicon carbide sintered body produced by the second production method coated with silicon carbide has not only high strength but also excellent thermal shock resistance, so that the temperature can be raised and lowered at a high temperature. It is extremely suitable as a member for a wafer heat treatment apparatus and a jig which requires severe and more complete prevention of contamination, for example, a member for manufacturing an SOI (Silicon On Insulator) wafer by a SIMOX (Silicon Implanted Oxide) method. is there.
[0046]
【Example】
"Example 1"
100 parts by weight of high-purity α-SiC powder having an average particle diameter of 10 μm and 70 μm and a weight ratio of 30:70 as raw material silicon carbide (SiC) powder, and 15 parts by weight of a resol-type phenol resin and aluminum 0 as a resin also used as a carbon source .18 parts by weight (1 part by weight of aluminum with respect to 100 parts by weight of Si powder) of 18 parts by weight of a high-purity Si powder having an average particle size of 5 μm dissolved and kneaded, granulated, and put into a rubber mold; CIP molding was performed at room temperature under a pressure of 100 MPa to obtain a cured molded body.
[0047]
The molded body was preliminarily fired at 1550 ° C. and a reduced pressure of 20 Torr, and then main fired at 2200 ° C. and a vacuum of 10 Torr, followed by reaction sintering.
The obtained porous sintered body had a bulk density of 1.88 g / cm, a porosity of 39%, a pore diameter of 14 μm, an l / r of 0.7, and a three-point bending strength of 48 MPa. The content of the impurity metal is as follows: Fe is 0.01 ppm, and as other impurity metals, K: less than 0.01 ppm, Na: less than 0.01 ppm, Ca: 0.04 ppm, Ni: 0.01 ppm, Cr: less than 0.01 ppm, Al: 0.10 ppm, Cu: less than 0.01 ppm, Mg: less than 0.01 ppm, Zn: less than 0.01 ppm, Mn: less than 0.01 ppm. When the cross section of the porous sintered body was observed with a TEM, it was confirmed that 85% or more of the Al-existing portion was the neck portion in terms of the area ratio on the observation screen.
Further, the above-described CVD treatment (twice) was performed using the porous sintered body as a base material. The strength of the porous silicon carbide sintered body (film thickness 120 μm) coated with the silicon carbide film was 185 MPa.
[0048]
"Comparative Example 1"
A porous sintered body was obtained in the same manner as in Example 1 except that the Si firing powder was not used and the main firing temperature was set at 2000 ° C.
The porosity of this porous sintered body was 30%, the average pore diameter was 7 μm, the l / r was 0.3, the bending strength was 28 MPa, and the Fe concentration as an impurity metal was 0.16 ppm.
It was found that the porous sintered body of Comparative Example 1 in which no Si fine powder was blended had a small l / r and was inferior in strength.
[0049]
"Comparative Example 2"
A porous sintered body was obtained in the same manner as in Example 1, except that the calcination temperature was 1400 ° C and the main calcination temperature was 1550 ° C.
The porosity of this porous sintered body was 39%, the pore diameter was 12 μm, the l / r was 0.3, the bending strength was 11 MPa, and the Fe concentration as an impurity metal was 11 ppm.
It was found that the porous sintered body of Comparative Example 2 having a low firing temperature had a small l / r, a low strength, and an inferior purity level.
[0050]
"Comparative Example 3"
A porous sintered body was obtained in the same manner as in Example 1, except that the resin was not added and a very small amount (about 3 parts by weight) of methylcellulose was added as a binder.
The porosity of this porous sintered body was 34%, the pore diameter was 5 μm, the l / r was 0.5, and the strength was 36 MPa.
The porous sintered body of Comparative Example 3 in which the carbon source resin was not blended had a slightly smaller l / r and was slightly inferior in strength.
[0051]
"Comparative Example 4"
In Example 1, after sintering at 1800 ° C. without adding Si fine powder to the raw materials of the example, the C source derived from the resin was silicified in a Si-containing atmosphere to obtain a porous sintered body.
The porous sintered body had a porosity of 27%, a pore diameter of 0.4 μm, an l / r of 0.4, and a strength of 28 MPa.
Since the Si source was supplied in a later step instead of the starting material and the firing temperature was further lowered, the l / r of the porous sintered body was small and the strength was poor.
Further, a porous silicon carbide sintered body coated with a silicon carbide film using the porous sintered body as a base material has a small pore diameter of 0.4 μm and is not deposited on the inside of the base material by CVD. The strength was as low as 55 MPa.
[0052]
"Example 2"
An aqueous slurry prepared by mixing 100 parts by weight of silicon carbide fine powder having an average particle size of 0.9 μm, 3 parts by weight of methyl cellulose as a binder, 1 part by weight of a nonionic surfactant as a dispersant, and 55 parts by weight of pure water. It was poured into a gypsum mold, slip cast molded, dried, calcined at 1200 ° C. and a reduced pressure of 10 Torr, and then sintered at 2200 ° C. to recrystallize crystal grains to obtain a porous sintered body. .
When the physical properties of this porous sintered body were evaluated in the same manner as in Example 1, the porosity was 42%, the average pore diameter was 3 μm, the l / r was 1.0, the bending strength was 94 MPa, and the Fe concentration as an impurity metal was 0.08 ppm. Met.
The strength of the CVD SiC-coated porous silicon carbide sintered body (film thickness: 120 μm) which was subjected to the CVD treatment (twice) using this porous sintered body as a base material was 246 MPa.
[0053]
"Comparative Example 5"
A porous sintered body was obtained in the same manner as in Example 2 except that the preliminary firing was not performed and the main firing temperature was set to 1200 ° C.
The porosity of this porous sintered body was 42%, the average pore diameter was 0.2 μm, the l / r was 0.4, the bending strength was 20 MPa, and the Fe concentration was 17 ppm.
It was found that the porous sintered body of Comparative Example 5 having a low firing temperature had a small l / r, a low strength, and a low purity level.
[0054]
"Comparative Example 6"
A porous sintered body was obtained in the same manner as in Example 2, except that α-SiC powder having an average particle size of 10 μm was used as the raw material SiC.
The porosity of this porous sintered body was 52%, the pore diameter was 12 μm, l / r was 0.55, and the strength was 19 MPa.
Since the average particle size of silicon carbide is too large, the porosity is as large as 52%, and the strength is significantly reduced.
[0055]
"Example 3"
In Examples 1 and 2, the main sintering temperature was changed, samples before the CVD treatment were prepared, and three-point bending strength measurement was performed. In addition, the size of the sample was set to 6 × 8 × 40 mm.
The result is shown in FIG.
R in FIG. 3 is based on the first manufacturing method (Example 1), and it has been found that sintering (main firing) at a temperature of 2000 ° C. or more is required to obtain a bending strength exceeding 40 MPa. In addition, S in FIG. 3 was obtained by the second manufacturing method (Example 2), and it was found that sintering at a temperature of 1500 ° C. or more was necessary to obtain a bending strength exceeding 40 MPa.
[0056]
"Example 4"
In Examples 1 and 2, samples were prepared by changing the thickness of the silicon carbide film, and three-point bending strength measurement was performed. The size of the sample was set to 3 × 4 × 40 mm, and the film formation conditions were: SiCl ₄ : C ₄ H ₁₀ : H ₂ = 5: 1: 10, 1200 ° C., 40 Torr.
The result is shown in FIG.
R in FIG. 5 is based on the first manufacturing method (Example 1), and the strength is 197 MPa when the surface layer thickness is 220 μm after four CVD processes, and the strength is 183 MPa when the surface layer thickness is 120 μm after the two CVD processes. In order to obtain a high-strength CVD-coated porous sintered body having a strength exceeding 180 MPa, a film thickness of 120 μm or more was found to be preferable.
Further, S in FIG. 5 is based on the second manufacturing method (Example 2), and the strength is 298 MPa when the surface layer thickness is 220 μm by four CVD processes, and the strength is when the surface layer thickness is 120 μm by the two CVD processes. It was found to be 264 MPa.
[0057]
"Example 5"
The thickness of the CVD film deposited on the SiC particles inside the pores was determined for the sample (porous sintered body after the second CVD coating (CVD SiC surface layer thickness: 120 μm)) prepared in the same manner as in Examples 1 and 2. The relationship between the pores and the position in the depth direction from the substrate interface was examined. The result is shown in FIG.
R in FIG. 4 is based on the first manufacturing method (Example 1). From the figure, it was found that CVDSiC completely filled pores between particles at the interface of the base material. Closed pores are observed at several tens μm from the interface, and further toward the center, open pores with a CVD silicon carbide film are formed, and the film thickness on the internal particles gradually decreases. However, it was found from the figure that a CVD film of about 0.5 μm was deposited even at a depth of 800 μm.
Further, S in FIG. 4 is based on the second manufacturing method (Example 2). Also in the case of this CVD-coated porous sintered body (S material), CVDSiC completes pores between particles at the interface of the base material. Embedded in Closed pores are observed at a distance of several μm from the interface, and further toward the center, open pores with a CVD silicon carbide film are formed, and the film thickness on the internal particles gradually decreases. From the figure, it was found that a CVD film having a depth of 100 μm and a thickness of about 0.2 μm was deposited.
[0058]
"Example 6"
In the process of manufacturing a SIMOX SOI wafer, oxygen ions are implanted into the wafer at about 600 ° C., and then the wafer is rapidly heated from 600 to 1000 ° C. to 1340 to 1350 ° C. Therefore, even when the boat used for the above is exposed to severe conditions such as the above-mentioned rapid rise in temperature, excellent heat shock that does not cause inconveniences such as film peeling, chipping, and extremely low strength. It is required to have characteristics.
[0059]
Therefore, the following evaluation tests were respectively performed.
(Heat shock resistance (ΔTc))
ΔTc, three-point bending strength and ΔTc of the porous sintered body sample (base material size of 2.5 × 3.5 × 40, film thickness of 220 μm) prepared according to Examples 1 and 2 measured by an underwater quenching method 6 is shown in FIG.
R in FIG. 6 is based on the first manufacturing method, and the bending strength of this sample (R material) does not decrease even at the maximum measurable (quenching) temperature difference of 1200 ° C., and therefore the ΔTc value is higher than 1200 ° C. I found it. Further, in the sample after quenching in water, no peeling of the film, no crack, and no increase in weight after immersion in water were observed.
S in FIG. 6 is based on the second manufacturing method (Example 2), and the bending strength of this sample does not decrease to the maximum measurable temperature difference of 1200 ° C., and therefore the ΔTc value is 1200 ° C. or more. I understand. Further, in the sample after quenching in water, no peeling of the film, no crack, and no increase in weight after immersion in water were observed.
[0060]
(Accelerated verification test by thermal cycle)
The samples prepared according to Examples 1 and 2 were placed in a furnace at 1200 ° C. at a stretch, heated for 20 minutes, carried out of the furnace at a stretch, and again carried into the furnace four times, and then for 16 hours. Perform nitric acid cleaning. This was repeated, and the presence or absence of explosion, film peeling, chipping, delamination, occurrence of cracks, and the like were confirmed.
In the samples prepared in Examples 1 and 2, no explosion, chipping, delamination, or change in weight after washing was observed up to 50 heat cycles.
[0061]
(High temperature strength measurement)
The 3 × 4 × 40 mm size samples prepared in Examples 1 and 2 were measured for strength up to 1400 ° C. in an Ar atmosphere. The thickness of the silicon carbide film was set to 220 μm by performing the CVD process four times. FIG. 7 shows the result.
In the samples prepared according to Examples 1 and 2, there was no decrease in strength up to 1400 ° C.
[0062]
【The invention's effect】
According to the present invention, it is possible to obtain a silicon carbide porous sintered body and a method for producing a silicon carbide porous sintered body having sufficiently high purity and high strength as members used in the semiconductor manufacturing industry.
Further, a porous silicon carbide sintered body and a silicon carbide porous sintered body having the above-described porous silicon carbide sintered body as a base material, and having a silicon carbide film formed on the surface thereof, having improved thermal shock resistance and strength characteristics. A method for producing the body can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a bonding state of SiC particles.
FIG. 2 is a schematic diagram showing a state in which a silicon carbide film is formed on a porous silicon carbide sintered body.
FIG. 3 is a graph showing the relationship between the firing temperature and the three-point bending strength of the porous sintered material (R material, S material) according to the present invention.
FIG. 4 is a graph showing a relationship between a depth distance from an interface between a deposited film and a substrate and a deposited thickness of SiC in pores in a SiC-coated porous silicon carbide sintered body according to the present invention.
FIG. 5 is a graph showing the relationship between the film thickness and the three-point bending strength of the SiC-coated porous silicon carbide sintered body according to the present invention.
FIG. 6 is a graph showing the relationship between the bending strength and the thermal shock resistance (ΔTc) of the SiC-coated porous silicon carbide sintered body according to the present invention.
FIG. 7 is a graph showing measurement results of temperature and three-point bending strength of a porous silicon carbide sintered body coated with SiC according to the present invention.
[Explanation of symbols]
1 (porous silicon carbide sintered body) substrate
2 Silicon carbide film
2a Silicon Carbide Film Formed on Silicon Carbide Crystal Particles
3 Porous silicon carbide sintered body (with silicon carbide film formed)
4 Interface
5 closed pores
6 open pores
7 Silicon carbide crystal particles
l Neck diameter
r particle size
N neck

Claims (11)

A porous silicon carbide sintered body having a porosity of 30% or more and 50% or less and a pore diameter of 0.2 μm or more and 20 μm or less, wherein neck diameter / particles of silicon carbide particles constituting a skeleton of the porous sintered body A porous silicon carbide sintered body having a diameter ratio of 0.6 or more. The aluminum concentration in the porous silicon carbide sintered body is 0.1 to 3 ppm, and 80% or more of the aluminum concentration is present in a neck portion to which silicon carbide particles are bonded. Porous silicon carbide sintered body. 2. The porous silicon carbide sintered body according to claim 1, wherein the porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and coated on the inside of the open pores of the base material by a CVD method. Union. 4. The porous silicon carbide sintered body according to claim 3, wherein pores of at least a surface layer of the base material are formed as closed pores by the silicon carbide film. 5. After adding a resin serving as a carbon source and silicon powder having an average particle diameter of 1 to 20 μm to silicon carbide raw material powder having an average particle diameter of 1 to 100 μm and cold isostatic pressing, the molded body is heated A method for producing a porous silicon carbide sintered body, comprising performing reaction sintering at 1800 to 2300 ° C. under reduced pressure at 0.01 to 10 Torr. The porous silicon carbide sinter according to claim 5, wherein the molded body is pre-fired at a temperature of 1400 to 1600C and a degree of reduced pressure of 1 to 50 Torr before being subjected to the reaction sintering under the reduced pressure. How to make the body. The method for producing a porous silicon carbide sintered body according to claim 5, wherein 1 to 3 parts by weight of aluminum is added by being dissolved in the silicon powder or added separately. The method according to any one of claims 5 to 7, wherein the porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and coated on pores of the base material by a CVD method. A method for producing a porous silicon carbide sintered body. After a slurry comprising a silicon carbide powder raw material having an average particle size of 1.5 μm or less, a binder and a dispersant is slip-cast molded, the molded body is sintered at a temperature of 1500 ° C. to 2200 ° C. A method for producing a porous silicon carbide sintered body, characterized by recrystallizing crystal grains. The method for producing a porous silicon carbide sintered body according to claim 9, wherein the molded body is preliminarily fired at 1100 to 1500C before sintering. The porous carbonized material according to claim 9, wherein the porous silicon carbide sintered body is used as a base material, and a silicon carbide film is deposited and coated to the inside of the pores of the base material by a CVD method. A method for producing a silicon sintered body.

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