Jig for heat treatment and process for fabricating the jig

Abstract: A jig used for heat treatment made from an SiC-coated silicon carbide material, wherein the SiC film is coated by the CVD method on a silicon carbide matrix in which silicon has been impregnated and wherein there are no pores with a diameter of 2 µm or larger in the outer layer of the matrix within 200 µm from the interface of the SiC film and the silicon carbide matrix when observed by a scanning electron microscope at a magnification of 400 times. The jig is manufactured by producing an SiC film on the surface of a silicon carbide matrix in which silicon has been impregnated by introducing a raw material compound for producing the SiC film and forming the SiC film at a temperature from 1000°C to 1290°C under a pressure from 500 to 760 Torr in a non-oxidative atmosphere. The jig exhibits superior resistance to high temperature heating cycles and excellent high thermal shock resistance required for heat treatment in semiconductor manufacturing.

Description: The present invention relates to a jig used for heat treatment made from an SiC-coated silicon carbide material and a process for manufacturing such a jig. It is known from EP 0 427 294 A1 and from Patent Abstracts of Japan, vol. 018, no. 357 (C-1221), 6 July 1994 and JP 06 092761 A (Shin Etsu Chem Co Ltd.) 5 April 1994 that the silicon carbide coating is formed by a CVD technique in which the SiC film is coated on an SiC matrix. The silicon carbide substrate is placed in a CVD furnace through which a reactant gas is passed whereby a coating is formed on the substrate. The furnace is generally maintained at a temperature of 1200 - 1350°C and at an atmospheric or reduced pressure of 1333,33 - 7999,99 N/m 2 (10 - 60 Torr). The content of free silicon in the coating may be controlled by changing the concentration and flow rate of the reactent gas, pressure and temperature. It is further known from Chemical Abstracts, volumn 116, no. 26, 29 June 1992 Columbus, Ohio, US; abstract no. 261139z, XP000374994 and JP 04 042 878 A (Tokai Carbon KK) 13 February 1992 that sintered SiC articles have an average pore size of 5 - 50 µm and a pore size distribution range of 1 - 100 µm can be impregnated with Si for reinforcement. This can be achieved by sintering of blended SiC powders in N-atmosphere. The formation of an SiC film is very effective for preventing vaporization of impurities. However, when the SiC film is formed by the CVD method on the silicon carbide substrate in which silicon has been impregnated, resistance to high temperature heating cycles and high termal shock resistance delicately change according to the conditions of the interface between the matrix and the SiC coating layer. This can cause cracks in the SiC film or peeling of the SiC film, when the product is used as a semiconductor part which may suffer from a severe heat history. In addition, part of the silicon impregnated in the silicon carbide matrix may easily vaporize and produce pores close to the surface of the substrate, resulting in impaired adhesion of the SiC film to the silicon carbide substrate. This will cause peeling of the SiC film from a heat shock or high temperature heat cycles. Furthermore, if pinholes are produced due to impaired adhesion of the SiC film, part of the impregnated silicon may be eroded and dissolved out, thereby producing pores. Such pores permit impurities to accumulate and can be a source of such impurities. To resolve the above-mentioned problems existing in the conventional process for producing an SiC film by chemical vapor deposition on the silicon-impregnated silicon carbide substrate used as semiconductor manufacturing parts, the present inventors have conducted extensive studies on the relationship between the properties in the interface of the substrate and the SiC coating layer and heat resistance characteristics of the resulting silicon carbide substrate, the factors for the formation of pores in the course of the SiC film production, and the like, on the basis of the above-mentioned process for forming an SiC film wherein the film formation is initiated in a temperature range of 850 - 1000°C. It is an object of the present invention to provide a jig for heat treatment in the manufacture of semiconductors with excellent durability during heat cycles and wherein the SiC is coated with closer adhesion to the silicon carbide substrate than that obtained by the already known chemical vapor deposition method. The above-mentioned objects can be achieved by a jig as claimed in claim 1 and a method as claimed in claim 3. The strength of the bond between an SiC film layer and a ceramic substrate when the former is coated onto the surface of the latter by the chemical vapor deposition method is greatly affected by the closeness and adhesion of the interface section. In particular, in the silicon-impregnated silicon carbide substrate on which an Sic film has been coated, tightness or closeness of the structure within 200 µm from the interface of the silicon carbide substrate and the Sic film greatly affects the strength of the bond between the CVD layer and substrate. If pores with a diameter larger than 2 µm exist within a depth of 200 µm, cracks or peeling may occur when the product is subjected to a severe heat history. According to the present invention, resistance to high temperature heating cycles and high thermal shock resistance which can withstand a severe heat history can be obtained by a structure wherein there are no pores with a diameter of 2 µm or larger in the outer layer of the silicon carbide substrate within 200 µm from the interface of the SiC film and the substrate. The pore diameter here is that observed in a measurement using a scanning type electron microscope at a magnification of 400 times. The high thermal shock resistance of the material is increased by increasing the orientation of SiC film crystals to the (111) plane in X-ray diffraction by keeping the ratio of the diffraction intensity of the (200) plane to the (111) plane, I(200)/I(111), 0.005 or less. In this instance, the value of X-ray diffraction intensity is that measured by the K α line of Cu, and X-ray diffraction intensity is measured under conditions of an accelarated voltage of 40 KV, an electric current of 20 mA, filter Cu/Ni, and a divergence slit of 1° . Furthermore, the process for manufacturing the jig for heat treatment of the present invention comprises producing an Sic film on the surface of a silicon carbide substrate in which silicon has been impregnated by introducing a raw material compound for producing the SiC film and forming the SiC film at a temperature from 1000°C to 1290°C under a pressure from 66.666, 66 - 101.333, 33 N/m 2 (500 to 760 Torr) in a non-oxidative atmosphere. Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The silicon-impregnated silicon carbide used as the substrate in the present invention is that produced by impregnating fused silicon in recrystallized silicon carbide which has been produced by sintering a formed body of silicon carbide at a high temperature. Alternatively, such a substrate may be sintered silicon carbide produced from a formed body of silicon carbide and carbon by impregnating fused silicon and treating it at a high temperature. The silicon content in thens matrixes is about 5-30wt%. The process for forming an SiC film on the surface of such a silicon-impregnated silicon carbide substrate by the surface of the chemical vapor deposition method preferably comprises a first step of degassing the silicon-impregnated silicon carbide substrate at a pressure of 1 Torr or less and heating at a temperature of 600-850°C at a heating rate of 5-50°C /min, a second step of introducing a non-oxidative gas until the pressure reaches 6.666, 66 - 101.333, 33 N/m 2 (50-760 Torr) and heating to 1000-1290°C at a heating rate of 5-50°C/min, and a third step of introducing a raw material for silicon carbide together with a carrier gas and forming a silicon carbide film at a temperature of 1000-1290°C and (500-760 Torr) 66.666, 66 - 101.333, 33 N/m 2 . Given as examples of the'raw material compound are organo silicon compounds containing Si and C in a molecule, such as methyltrichlorosilane (CH 2 SiCl 3 ) and methyldichlorosilane (CH 2 SiHCl 2 ). Alternatively, a combination of a silicon compound such as SiCl 4 and a carbon compound such as CH 4 may be used. As a carrier gas, a non-oxidative gas such as hydrogen gas or argon gas can be given as examples. It is desirable that the carrier gas and the raw material compound be introduced at a molar ratio of (carrier gas/raw material compound) of 4-100. When a silicon compound and a carbon compound are used in combination, the molar ratio reduced to silicon carbide is applicable. The heating rate in the first and second steps is 5-50°C/min. If this heating rate exceeds 50°C/min, thermal stress may be produced in the substrate which may cause crack. If lower than 5°C/min, productivity is impaired. A preferred range for the rate of temperature rise is 10-30°C/min. If the pressure after degassing is higher than 1 Torr in the first step, the surface of silicon carbide substrate may be oxidized by residual oxygen or moisture, which may decrease the corrosion resistance and adhesion of the silicon carbide film to the substrate. A heating temperature lower than 600°C in the first step is undesirable, because adsorbed oxygen is removed only insufficiently and may eaaily oxidize the surface of the silicon carbide substrate. On the other hand, a heating temperature higher than 850°C causes silicon to evaporate under reduced pressure and pores tends to be easily produced in the silicon carbide substrate, resulting in decreased adhesion of the silicon carbide film to the substrate. If the pressure is higher than 101.333, 33 N/m 2 (760 Torr) in the second step, hydrogen gas may easily escape, resulting in needless consumption of hydrogen gas. In addition, a higher pressure requires reinforced pressure vessels and complicated equipment. In the second and third steps, the heating rate and conditions of the CVD reaction system, such as temperature and pressure, are controlled below the vapor pressure of silicon to prevent the silicon impregnated in the silicon carbide substrate from being vaporized from the surface of the substrate. The jig for heat treatment of the present invention which consists of the SiC-coated silicon carbide can be obtained only by controlling the conditions in the second and third steps in this manner. Specifically, if the pressure in the second step is less than 50 Torr, or if the temperature is more than 1290°C or the pressure is less than 66.666, 66 N/m 2 (500 Torr) in the third step, impregnated silicon existing in the outer layer of the silicon carbide substrate may vaporize with heat, producing pores in the outer layer of the substrate. Furthermore, if the heating temperature is lower than 1000°C in the third step, the growing rate of the SiC film is suppressed, even if vaporization of silicon is decreased. In addition, if the pressure is in excess of 760 Torr in the third step, silicon carbide powder is produced before the gas of the raw material compound is deposited on the surface of the silicon carbide substrate, thereby suppressing the rate of formation of the SiC film. In addition to suppressing pore generation in the substrate by the application of these conditions, crystals of the SiC film with high thermal shock resistance produced by chemical vapor deposition can be improved by causing the SiC crystals of the (111) plane to be highly oriented on the substrate. This can be achieved by controlling the molar ratio of the carrier gas, such as hydrogen or argon, and the raw material compound at 4-100, preferably 5-20, under conditions of a temperature of 1100-1290°C and a pressure of 66.666, 66 - 101.333, 33 N/m 2 (500-760 Torr). If the temperature is lower than 1100°C, the high thermal shock resistance of the SiC film is reduced. If the molar ratio of the carrier gas and the raw material compound is less than 4, crystal nuclei are easily produced on the surface of the silicon carbide substrate. This tends to roughen the SiC film formed and reduces its minuteness; if this molar ratio is more than 100, polycrystals are easily produced in the SiC film and the orientation of SiC crystals in the (111) plane may decrease. Cracks are produced or peeling occurs in the interface of the silicon-impregnated silicon carbide substrate and the SiC coating film produced by the chemical vapor deposition method when the material is subjected to severe heat cycles such as encountered by a jig for heat treatment. The major reason for this is that the silicon impregnated when the coating is provided by chemical vapor deposition is vaporized to produce pores with a diameter larger than 2 µm in the layer of the silicon carbide substrate within 200 µm from the interface of the SiC film. Because the heat treatment jig of the present invention is free from such pores with a diameter larger than 2 µm in the silicon carbide substrate within 200 µm from the SiC coating film, the SiC film adheres firmly to the silicon carbide substrate and the jig exhibits excellent durability to severe heat cycles involving rapid heating and cooling. In addition, the orientation of the crystal structure of SiC film to the (111) plane can be increased by setting the ratio I(200)/I(111) of the value of X-ray diffraction intensity of the SiC film at 0.005 or less. The chemical bonding strength of silicon carbide, silicon, and the SiC film constituting the silicon carbide substrate is increased because the (111) plane is closest packing structure, whereby the high thermal shock resistance of the SiC film is further increased. Other features of the invention will become apparent in the course of the following description of the exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. EXAMPLES Examples 1-6, Comparative Examples 1-2 Silicon in the amount of 20 wt% was impregnated in recrystallized silicon carbide of 50×50×10 mm to produce a silicon carbide matrix. This matrix was placed in a circular furnace and degassed under a vacuum of 0,2 66 N/m 2 (2 × 10 -3 Torr) After heating to 800°C at a rate of temperature rise of 20°C/minute, hydrogen gas was introduced to make a pressure of 19.999,99 N/m 2 (150 Torr). The furnace was maintained under these conditions for 30 minutes. Then, the temperature was raised at the rate of 20°C/minute to the temperatures listed in Table 1, and the furnace was maintained at these temperatures for 30 minutes. Then, the raw material compound (CH 3 SiCl 3 ) for forming the SiC film was supplied at the different molar ratios of H 2 /CH 3 SiCl 3 listed in Table 1. In this instance, the pressure in the furnace was adjusted by controlling the amount of the raw material supplied. SiC was coated on the silicon carbide substrate by changing the temperature and pressure in the furnace, and the molar ratio of raw material gas. Examples 7-9, Comparative Examples 3-4 A 50×50×10 mm sintered silicon carbide substrate (residual Si: 10 wt%) was degassed under the same conditions as in Example 1 and heated to 700°C at a temperature rise of 33°C/minute. Argon gas was introduced and the pressure was maintained at 300 Torr for 20 minutes. Then, the temperature was raised at the rate of 10°C/minute to the temperatures listed in Table 2 and the raw material compounds (SiCl 4 and CH 4 ) for forming the SiC film were supplied at the different molar ratios of 2Ar/SiCl 4 +CH 4 listed in Table 2. SiC was coated on the silicon carbide substrate by controlling the temperature and pressure in the furnace in the same manner as in the Examples 1-6. Comparative Example 5 The same silicon carbide substrate was degassed under the same conditions as in the Example 1-6. After heating to 950°C at a temperature rise of 20°C/minute, hydrogen gas was introduced and the substrate was allowed to stand for 30 minutes under a pressure of 150 Torr. After heating to 1300°C at a temperature rise of 20°C/minute, a raw material gas (at a molar ratio H 2 /CH 3 SiCl 3 4.0) was introduced while maintaining the pressure in the furnace at 26.666, 66 N/m 2 (200 Torr) to produce an SiC film on the silicon carbide substrate. Comparative Example 6 The same sintered silicon carbide substrate as used in the Example 7 was degassed under the same conditions as in the Example 1-6. After heating to 1100°C at a temperature rise of 10°C/minute, argon gas was introduced and the substrate was allowed to stand for 20 minutes under a pressure of 1.999, 99 N/m 2 (15 Torr). After heating to 1200°C at a temperature rise of 20°C/minute, a raw material gas consisting of SiCl 4 and CH 4 was supplied at a molar ratio of (2Ar/SiCl 4 +CH 4 ) of 2.5 while maintaining the pressure in the furnace at 5.333, 33 N/m 2 (40 Torr). The resulting SiC-coated silicon carbide materials obtained in the above-mentioned Examples and Comparative Examples were cut and the cross-sections were observed using a scanning electron microscope at a magnification of 400 times to confirm presence of pores with a diameter larger than 2 µm existing in the outer layer within the depth of 200 µm. Furthermore, the X-ray diffraction intensity was measured to determine the ratio I(200)/I(111). The X-ray diffraction was measured under the conditions of an applied voltage of 40 KV, an electric current of 20 mA, filter Cu/Ni, and a divergence slit of 1°. The temperature and pressure in the furnace when the SiC films are formed, the molar ratio of the raw material gases, the presence or absence of pores with a diameter of 2 µm or more in the silicon carbide matrix within 200 µm of the interface of the SiC film and the matrix, the X-ray diffraction intensity, and the ratio of the diffraction intensity are shown in Table 1 and Table 2. SiC film forming conditions 2 µm or larger pores X-ray diffraction Temp. °C Pressure (N/m 2 ) Raw material gas I (200) I (111) Ratio Example 1 1000 101333, 33 A 9.0 None 60 1,0985 0.0055 2 1100 101333, 33 A 9.0 None 84 19095 0.0044 3 1200 101333, 33 A 9.0 None 0 34410 0.0000 4 1250 101333, 33 A 7.3 None 0 62281 0.0000 5 1200 66666, 66 A 7.3 None 65 28836 0.0023 6 1265 101333, 33 A 7.3 None 25 41037 0.0006 Comparative Example 1 1300 101333, 33 A 9.0 Present 43 30866 0.0014 2 1200 59999, 99 A 7.3 Present 370 3481 0.1063 5 1300 26666, 66 A 4.0 Present 150 25000 0.0060 SiC film forming conditions 2 µm or larger pores X-ray diffraction Temp. (°C) Pressure (N/m 2 ) Raw material gas I (200) I (111) Ratio Example 7 1050 79999, 99 B 4.5 None 89 16790 0.0053 8 1150 101333, 33 B 15.0 None 15 54650 0.0003 9 1285 79999, 99 B 80.0 None 104 27311 0.0038 Comparative Example 3 1150 39999, 99 B 150.0 Present 420 14816 0.0283 4 1400 66666, 66 B 30.0 Present 74 82060 0.0023 6 1200 5333, 33 B 2.5 Present 370 3481 0.1063 Next, the resistance to high temperature heating cycles and high thermal shock resistance were tested on these Sic-coated silicon carbide materials according to the following methods. The resistance to high temperature heating cycles was evaluated by observing the presence or absence of cracks or peeling in the SiC films of the samples after 20 repetitions of a heating cycle consisting of heating the sample in an infrared heating furnace to 1300°C in 15 minutes, allowing the sample to stand at this temperature, then removing the sample from the furnace and leaving it to cool to the ambient temperature. The high thermal shock resistance was evaluated by observing the presence or absence of cracks or peeling in the SiC films of the samples after the sample was heated for 30 minutes at 500°C or 1000°C in an electric furnace, followed by quenching in water at 20°C. The results are shown in Table 3 and Table 4. Resistance to high temperature heating cycles High thermal shock resistance Heating temperature (500°C) Heating temperature (1000°C) Example 1 No abnormality No abnormality Slight peeling 2 No abnormality No abnormality No abnormality 3 No abnormality No abnormality No abnormality 4 No abnormality No abnormality No abnormality 5 No abnormality No abnormality No abnormality 6 No abnormality No abnormality No abnormality Comparative Example 1 Cracks and slight peeling occurred. Cracks and slight peeling occurred. Cracks occurred and a part of the film peeled. 2 Cracks occurred and a part of the film peeled. Cracks occurred and a part of the film peeled. Cracks occurred and film peeled extensively. 5 Small cracks produced. Cracks and slight peeling occurred. Cracks occurred and a part of the film peeled. Resistance to high temperature heating cycles High thermal shock resistance Heating temperature (500°C) Heating temperature (1000°C) Example 7 No abnormality No abnormality Slight peeling 8 No abnormality No abnormality No abnormality 9 No abnormality No abnormality No abnormality Comparative Example 3 Cracks and slight peeling occurred. Cracks occurred and a part of the film peeled. Cracks occurred and film peeled extensively. 4 Small cracks produced. Small cracks and slight peeling occurred. Cracks occurred and a part of the film peeled. 6 Small cracks produced. Small cracks and slight peeling occurred. Cracks occurred and a part of the film peeled. The results shown in Tables 1-4 indicates that the SiC-coated silicon carbide materials of the present invention, in which there are no pores with a diameter of 2 µm or more in the outer layer of the silicon carbide substrate within 200 µm from the interface of the matrix and the SiC film, are free from production of cracks or peeling of the film even after repetition of heat treatment consisting of rapid heating and quenching and exhibit superior durability against a thermal shock consisting of quenching to 20°C from 500°C. In addition, it can be seen from the results of the quenching test to 20°C from 1000°C in Tables 3 and 4 that the durability with respect to heat shock is further increased by keeping the ratio I(200)/I(111) of the diffraction strength in the X-ray diffraction of the SiC film at 0.005 or less. In contrast, in the materials prepared in the Comparative Examples in which there are pores in the silicon carbide substrate, cracks were produced and the SiC film was peeled from the substrate. As described above, because the SiC-coated silicon carbide material of the present invention has superior resistance to high temperature heating cycles and excellent high thermal shock resistance, the material is useful as a jig for heat treatment in semiconductor manufacturing under severe temperature conditions involving rapid cooling from a high temperature to a low temperature. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims: A jig used for heat treatment made from an SiC-coated silicon carbide material, wherein the SiC film is coated by the CVD method on a silicon carbide substrate in which silicon has been impregnated and wherein there are no pores with a diameter of 2 µm or larger in the outer layer of the substrate within 200 µm from the interface of the SiC film and the silicon carbide matrix when observed by a scanning electron microscope at a magnification of 400 times. A jig used for heat treatment made from an SiC-coated silicon carbide material, wherein the SiC film is coated by the CVD method on a silicon carbide substrate in which silicon has been impregnated, wherein there are no pores with a diameter of 2 µm or larger in the outer layer of the substrate within 200 µm from the interface of the SiC film and the silicon carbide matrix when observed by the scanning electron microscope at a magnification of 400 times and wherein the ratio of the X-ray diffraction intensity of the (200) plane of the (111) plane of the SiC film, I(200)/ I(111), is 0.005 or less. A process for manufacturing a jig for heat treatment which comprises producing an SiC film on the surface of a silicon carbide substrate impregnated with silicon by introducing a raw material compound for producing the SiC film together with a carrier gas at a molar ratio of the carrier gas and the raw material compound of 4 to 100 and forming the SiC film at a temperature from 1100 - 1290°C under a pressure from 6,666 x 10 4 N/m 2 - 10,13 x 10 4 N/m 2 (500 - 760) Torr in a non-oxidative atmosphere. The process according to claim 3, wherein the molar ratio of the carrier gas and the raw material compound is from 5 to 20. A process for manufacturing a jig for heat treatment which comprises a first step of degassing a silicon-impregnated silicon carbide substrate at a pressure of 133, 33 N/m 2 (1 Torr) or below and heating at a temperature of 600 - 850°C at a heating rate of 5 - 50°C/min, a second step of introducing a non oxidative gas until the pressure reaches 6.666, 66 - 101.333, 33 N/m 2 (50 - 760 Torr) and heating to 1000 - 1290°C at a heating rate of 5 - 50°C/ min, and a third step of introducing a raw material for silicon carbide together with a carrier gas and forming a silicon carbide film at a temperature of 1000 - 1290°C and 6,666 x 10 4 N/m 2 - 10,13 x 10 4 N/m 2 (500 - 760 Torr).

Inventors: FUNATO YOSHIO, FURUKAWA KOJI, KAGEYAMA NOBUO, YAMAMOTO HISAO, FUNATO, YOSHIO, FURUKAWA, KOJI, KAGEYAMA, NOBUO, YAMAMOTO, HISAO, Funato, Yoshio, c/o Tokai Carbon Comp. Ltd., Furukawa, Koji, c/o Asahi Glass Comp. Ltd., Kageyama, Nobuo, c/0 Asahi Glass Comp. Ltd., Yamamoto, Hisao, c/o Asahi Glass Comp. Ltd.
Applicants: ASAHI GLASS CO LTD, TOKAI CARBON COMPANY LTD, ASAHI GLASS COMPANY LTD., TOKAI CARBON COMPANY LTD.
Application year: 1996
Main classification: C04B41
IPC codes: H01L21, C23C16, C04B41