JP2015127269A - Sintered compact of silicon carbide and producing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered compact of silicon carbide and a producing method thereof in which suppression of generation frequency of crack etc. due to baking shrinkage in a formed product is achieved.SOLUTION: There is provided a producing method of a ceramic sintered compact in which, by precipitating a part of ingredient powder with elutriation subjected to slurry obtained from supplementation of distribution agent and solvent to ceramic ingredient powder, supernatant of the slurry is recovered, then a formed product is produced by forming a cake of the ingredient powder in the supernatant, and the formed product is subjected to calcination. Due to the elutriation, y% or more of ingredient powder among ingredient powder having a larger diameter than criterion particle diameter to be x% as accumulation in early stage particle diameter distribution is removed. The elutriation is carried out so that 2 dimensional plot (x, y) is positioned in first specified region S1 or second specified region S2.

Description

  The present invention relates to a silicon carbide sintered body and a method for producing the same.

  Silicon carbide-based sintered bodies are used for semiconductor manufacturing apparatuses, liquid crystal manufacturing apparatus members, chuck members, and the like in view of the characteristics of high thermal conductivity and high Young's modulus. On the other hand, residual stress derived from unevenness of shrinkage at the time of molding of the silicon carbide powder or firing of the molded body, or local pores remain in the sintered body, resulting in stress release during processing of the sintered body. Or there is a possibility of chipping or chipping based on the pores, and eventually damage. This possibility becomes higher as the size of the semiconductor wafer is increased, and as a result, the size of the silicon carbide sintered body as a constituent member of a semiconductor manufacturing apparatus is increased.

  Therefore, by adjusting the particle size distribution of the raw material powder, adjusting the blending amount of the auxiliary agent, etc., or improving the firing method, it becomes easier to sinter the molded body, and further suppresses the generation of voids and density variation in the sintered body, and the residual The stress is reduced (see Patent Documents 1 and 2).

JP 2001-247367 A JP 2006-240957 A

  However, since the silicon carbide powder as the raw material powder is obtained by crushing a large lump (ingot) of the raw material, it contains a relatively large amount of coarse particles. For this reason, the slurry containing the said raw material powder is adjusted, and local nonuniformity will arise in the density distribution of the molded object obtained by casting.

  Accordingly, an object of the present invention is to provide a silicon carbide based sintered body in which the occurrence frequency of cracks derived from firing shrinkage of a molded body is suppressed and a method for producing the same.

The present invention provides a method for producing a silicon carbide sintered body of the following [1] to [2] and a silicon carbide sintered body of [3] to [4].
[1] The maximum frequency is 12% or less, D50 is included in the range of 0.7 to 1.2 [μm], D90-D50 is included in the range of 0.7 to 1.1 [μm], And the process which adjusts a slurry by adding a pH adjuster and a solvent with respect to the silicon carbide powder in which D90-D10 is contained in the range of 1.2-1.6 [micrometers], and the elt with respect to the said slurry A step of recovering the supernatant of the slurry by precipitating a part of the raw material powder by the relation, a step of producing a molded body by molding the raw material powder contained in the supernatant, and firing the molded body And a step of producing a sintered body having a particle diameter larger than a reference particle diameter in which the particle size contained in the slurry is cumulative x% in the initial particle size distribution by the L-trilation. , Y% or more of the raw material powder is removed, a two-dimensional plot (x, y) is, four line segments in the x-y plane _{L 11: x = 70 (5} ≦ y ≦ 70), L 12: y = 2x -135 (70 ≦ x ≦ 95), L ₁₃ : included in the first designated area defined by x = 95 (55 ≦ y ≦ 95) and L ₁₄ : y = x (70 ≦ x ≦ 95) A method for producing a silicon carbide sintered body.
[2] The two-dimensional plot (x, y) includes four line segments L ₂₁ : x = 70 (25 ≦ y ≦ 70) and L ₂₂ : y = 2x−115 (70 ≦ x ≦) in the xy plane. _{85), L 23: y =} 4x-285 (85 ≦ x ≦ 95) , and _{L 24: y = x (70} ≦ x ≦ 95) is included in the second designated area is defined by [1], wherein the method of.
[3] A silicon carbide based sintered body produced by the method according to [1], having a Young's modulus of 415 [GPa] or more and a standard deviation of 13.0 [GPa] or less.
[4] A silicon carbide based sintered body produced by the method according to [2], having a Young's modulus of 417 [GPa] or more and a standard deviation of 8.0 [GPa] or less.

  According to the method of the present invention, an elutriation is applied to a slurry prepared from a raw material powder having a wide particle size distribution (see the broken line in FIG. 1) due to the presence of coarse particles. Thereby, a part of the coarse particles is removed, and a raw material powder having a narrowed particle size distribution (see the solid line in FIG. 1) is obtained. By using the raw material powder, the filling rate of the molded body is improved, and by firing, the shrinkage of the sintered body is homogenized and the relative density of the sintered body is improved. As a result, the Young's modulus of the sintered body is improved and the variation (standard deviation) in Young's modulus is reduced.

Explanatory drawing regarding the particle size distribution adjustment of the silicon carbide powder as raw material powder. Explanatory drawing regarding the particle size distribution of commercially available silicon carbide powder. Explanatory drawing of a 1st designated range and a 2nd designated range.

  The manufacturing method of the silicon carbide based sintered body as one embodiment of the present invention includes (1) a slurry adjustment step, (2) an elutriation step, (3) a molding step, and (4) a firing step. Contains.

(1) Slurry adjustment process After adding a pH adjuster and water with respect to silicon carbide powder, the slurry was adjusted by using a resin ball as a medium and milling. A pH adjuster will not be limited if it is a material which can adjust pH of a slurry to the range of 9-12.

  In the initial particle size distribution of the silicon carbide powder, (a) the maximum frequency is 12% or less, (b) D50 is included in the range of 0.7 to 1.2 [μm], and (c) D90− D50 is included in the range of 0.7 to 1.1 [μm], and (d) D90-D10 is included in the range of 1.2 to 1.6 [μm].

  In FIG. 2, the particle size distribution of commercial silicon carbide powder No. 1 is shown by a one-dot chain line, the particle size distribution of commercial silicon carbide powder No. 2 is shown by a two-dot chain line, and commercially available alumina for comparison. The particle size distribution of the powder is indicated by a broken line. The particle size distribution curve of the commercially available silicon carbide powder has a relatively low peak and is wide, while the particle size distribution curve of the commercially available alumina powder has a relatively high peak and a narrow width. The maximum frequency of the commercially available silicon carbide powder 1 is about 8%, D50 is 0.87 [μm], D90-D10 is 1.45 [μm], and D90-D50 is 0.96. [Μm]. The maximum frequency of commercially available silicon carbide powder No. 2 is about 10%, D50 is 1.01 [μm], D90-D10 is 1.37 [μm], and D90-D50 is 0.83. [Μm].

(2) L-triation step The slurry is placed in a container and allowed to stand for a predetermined period, and a relatively large diameter powder (coarse particles) is selectively deposited on the bottom surface of the container. An elutriation is performed in which the slurry staying in the supernatant of the accumulated large-diameter powder group is collected by a liquid feed pump or the like. The addition of the pH adjuster suppresses the aggregation and secondary powdering of the powder, promotes efficient classification in the state of the primary powder, and suppresses rapid sedimentation of the powder, thereby facilitating recovery.

  For example, the slurry prepared from the raw material powder having a relatively wide particle size distribution shown by a broken line in FIG. 1 is subjected to elutriation once or a plurality of times. Thereby, the slurry containing the raw material powder having a relatively narrow particle size distribution shown by the solid line in FIG. 1 is recovered.

The particle size distribution of the recovered raw material powder (see the solid line in FIG. 1) is a distribution range S (see the thick line in FIG. 1) larger than the standard particle size D _x of the initial particle size distribution of the raw material powder (see the broken line in FIG. 1). Of these, y% (see the hatched portion in FIG. 1) is removed. Reference diameter D _x denotes a particle size of which cumulative particle size distribution is x%, for example in the case of x = 50 corresponds to a median diameter D _50.

In the two-dimensional plot (x, y), four line segments L ₁₁ : x = 70 (5 ≦ y ≦ 70) indicated by a one-dot chain line in FIG. 3 in the xy plane, L ₁₂ : y = 2x− 135 (70 ≦ x ≦ 95), L ₁₃ : x = 95 (55 ≦ y ≦ 95) and L ₁₄ : y = x (70 ≦ x ≦ 95) so as to be included in the first designated region An e-triation is performed.

The two-dimensional plot (x, y) shows four line segments L ₂₁ : x = 70 (25 ≦ y ≦ 70) indicated by a two-dot chain line in FIG. 3 in the xy plane, and L ₂₂ : y = 2x. -115 (70 ≦ x ≦ 85), L ₂₃ : included in the second designated region defined by y = 4x−285 (85 ≦ x ≦ 95) and L ₂₄ : y = x (70 ≦ x ≦ 95) It is more preferable that the elutriation is performed as described above.

(3) Molding step A dispersant (or dispersant and sintering aid) is added to the recovered slurry and remixed. As the dispersant, a general dispersant such as a polycarboxylic acid-based dispersant or a polyacrylic acid-based dispersant is used. At this stage, a pH adjusting agent and water may be added in an insufficient amount to the slurry. The recovered slurry may be dried to obtain a raw material powder, and then a dispersant may be added to the raw material powder to adjust the slurry again. The slurry discharged from the mixing mill is subjected to vacuum stirring and defoaming after a binder is added. The slurry is poured into a gypsum mold, and a molded body is produced by casting. As the forming method, other methods such as waste mud casting or vacuum suction forming may be used.

(4) Firing step After the molded body is dried, a sintered body is obtained by being held in a predetermined temperature range in a vacuum or in an appropriate atmosphere.

(Example)
Example 1
After adding 0.5 parts by weight of tetraammonium hydroxide as a pH adjuster and 50 parts by weight of ion-exchanged water to 100 parts by weight of Stark UF-10 silicon carbide powder, The slurry was adjusted by milling for 18 hours.

  The slurry was placed in a container and allowed to stand for 5 hours, whereby a relatively large-diameter powder containing coarse particles was deposited on the bottom of the container. Further, the pH of the slurry was adjusted to 10.5, and the slurry viscosity was adjusted to 180 [mPa · s]. In this state, only the slurry retained in the supernatant was collected by the liquid feed pump. (X, y) = (70, 5).

  The position of the two-dimensional plot (x, y) is adjusted by adjusting the pH and viscosity of the slurry in addition to the standing time of the slurry in the container. By adjusting the pH of the slurry to a range of 9.0 to 12.0, aggregation (primary particle formation) of the silicon carbide raw material powder is suppressed. The slurry viscosity can be adjusted by the amount of water, the pH adjusting agent concentration, the amount of thickener added, etc., and by adjusting the slurry viscosity to 25 to 380 [mPa · s], the raw material powder contained in the slurry is settled. An excessively high speed is suppressed.

Stark 1500 F B ₄ C as a boron source and Tokai Carbon Co. Aqua Black001 as a carbon source were added to the recovered slurry. With respect to 100 parts by weight of silicon carbide, the boron source was adjusted to 0.6 parts by weight and the carbon source was adjusted to 3.0 parts by weight in solid content. A-6114 (polycarboxylic acid ammonium salt type) manufactured by Toagosei Co., Ltd. was added as a dispersant to 3.0 parts by weight based on the solid content of the carbon source. Further, after the raw material powder was milled again for 18 hours, 5.0 parts by weight of a binder was added to the resulting slurry, and the mixture was stirred and degassed for 1 hr.

(Molding process)
The slurry was poured into a plaster mold while being pressurized, and a substantially disk-shaped molded body having a diameter of 500 [mm] and a thickness of 20 [mm] was cast and molded. The outer periphery of the molded body was raw-processed to such an extent that impurities from gypsum did not enter.
(Baking process)
The molded body was held at 2050 [° C.] for 3.5 [hr] in a non-oxidizing atmosphere, whereby the silicon carbide based sintered body of Example 1 was produced.
(Examples 2 to 8)
Except for the aspect of adjusting the particle size distribution of the raw material powder represented by the two-dimensional plot (x, y) (see Table 1), the silicon carbide based sintered bodies of Examples 2 to 8 under the same conditions as in Example 1 It was made.

(Evaluation method)
The characteristics of the silicon carbide sintered body of each example were evaluated as follows. The particle size distribution of the raw material powder was measured using a Horiba / LA-920 laser diffraction / scattering type device. The relative density of the molded body was calculated based on the size and weight after raw processing. The relative density of the sintered body was calculated by the Archimedes method.

  The sintered body was equally divided into two in the thickness direction, and 10 test pieces were prepared by cutting out the central portion and each of the four portions equally spaced in the radial direction outside thereof. After confirming the presence or absence of cracks during processing, the Young's modulus of each test piece was measured according to a resonance method (JIS-1602) by JE-RT manufactured by Nippon Techno-Plus. The standard deviation σ (variation) of Young's modulus measurement results for 10 test pieces was evaluated.

  Table 1 collectively shows the measurement results of the characteristics of the molded body and the sintered body, along with the adjustment mode of the particle size distribution of the raw material powder, etc., for the silicon carbide sintered body of each example.

  In FIG. 2, a two-dimensional plot (x, y) of the sintered body of each example is represented by a circle with a corresponding number. As is clear from FIG. 2 and Table 1, no cracks are observed in the silicon carbide sintered bodies of Examples 1 to 8 in which the two-dimensional plot (x, y) is included in the first designated region S1. The Young's modulus was 415 to 425 [GPa], and the standard deviation σ was 5.0 to 13.0 [GPa]. The standard deviation σ of the Young's modulus of the silicon carbide based sintered bodies of Examples 2, 3, 5, 6 and 8 in which the plot (x, y) is included in the second designated region S2 is 5.0 to 8.0. [GPa], which is smaller than those of the other silicon carbide sintered bodies of Examples 1, 4 and 7.

(Comparative example)
The silicon carbide based sintered bodies of Comparative Examples 1 to 5 were produced under the same conditions as in Example 1 except for the aspect of adjusting the particle size distribution of the raw material powder represented by the two-dimensional plot (x, y). For the silicon carbide sintered body of each comparative example, together with the adjustment mode of the particle size distribution of the raw material powder, the observation results of the presence or absence of cracks in the molded body and the sintered body, and the measurement results of Young's modulus and standard deviation σ are collectively shown. Yes.

  In FIG. 2, a two-dimensional plot (x, y) of the sintered body of each comparative example is represented by a triangle with a number. As apparent from FIG. 2 and Table 2, among the silicon carbide based sintered bodies of Comparative Examples 1 to 5 in which the two-dimensional plot (x, y) deviates from the first designated region S1, Comparative Examples 3 and 5 Cracks were observed in the silicon carbide sintered body. The Young's modulus of the silicon carbide sintered bodies of Comparative Examples 1 and 2 is lower than that of any of Examples 1-8. The standard deviation σ of the Young's modulus of the silicon carbide sintered bodies of Comparative Examples 2 and 3 is larger than any of Examples 1-8.

S1... First designated area, S2... Second designated area.

Claims (4)

The maximum frequency is 12% or less, D50 is included in the range of 0.7 to 1.2 [μm], D90-D50 is included in the range of 0.7 to 1.1 [μm], and D90 A step of adjusting the slurry by adding a dispersant and a solvent to the ceramic raw material powder containing -D10 in the range of 1.2 to 1.6 [μm];
Recovering the supernatant of the slurry by precipitating a part of the raw material powder by elutriation to the slurry;
A step of producing a molded body by molding the raw material powder contained in the supernatant;
Producing a sintered body by firing the molded body,
By the L-trilation, y% or more of the raw material powder having a diameter larger than the reference particle diameter that is cumulative x% in the initial particle size distribution is removed, and a two-dimensional plot (x , Y) are four line segments L ₁₁ : x = 70 (5 ≦ y ≦ 70), L ₁₂ : y = 2x−135 (70 ≦ x ≦ 95), L ₁₃ : x = 95 in the xy plane. (55 ≦ y ≦ 95) and L ₁₄ : A method for producing a ceramic sintered body included in the first designated region defined by y = x (70 ≦ x ≦ 95). The two-dimensional plot (x, y) has four line segments L ₂₁ : x = 70 (25 ≦ y ≦ 70), L ₂₂ : y = 2x−115 (70 ≦ x ≦ 85) in the xy plane, The method according to claim 1, wherein the method is included in a second designated area defined by L ₂₃ : y = 4x−285 (85 ≦ x ≦ 95) and L ₂₄ : y = x (70 ≦ x ≦ 95).   A ceramic sintered body produced by the method according to claim 1 and having a Young's modulus of 415 [GPa] or more and a standard deviation of 13.0 [GPa] or less.   A ceramic sintered body produced by the method according to claim 2 and having a Young's modulus of 417 [GPa] or more and a standard deviation of 8.0 [GPa] or less.