JP2008127226A - Method of producing nitride compound sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a nitride compound sintered compact suitable for e.g. a susceptor, which shows reduced exposure of boron nitride particles of ≥10 μm or agglomerated particles containing the boron nitride particles. <P>SOLUTION: The method of producing the nitride compound sintered compact is a method of firing a nitride ceramic powder, provided that the nitride ceramic powder is prepared by removing a medium from a wet mixture of the medium and a nitride ceramic powder and that the medium is at least one chosen from hydrofluorocarbon and hydrofluoroether and contains 2-10 mass% alcohol. The alcohol is at least one chosen from ethanol, isopropyl alcohol and t-amyl alcohol, preferably t-amyl alcohol. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for producing a nitride composite sintered body.

Since the boron nitride sintered body has high corrosion resistance against high-temperature hydrogen chloride gas and ammonia gas, it is used as a member (susceptor) for semiconductor manufacturing equipment such as GaN. In particular, when the susceptor is a nitride composite sintered body made of boron nitride and a nitride other than boron nitride (for example, silicon nitride, aluminum nitride, etc.), in addition to the basic characteristics of high corrosion resistance, the thermal conductivity is high. Therefore, the temperature followability is good and the wear resistance is also excellent (Patent Document 1). Such a susceptor is manufactured through a step of molding and firing a mixed powder obtained by dry mixing or wet mixing raw materials. Since the specific gravity, particle diameter and particle shape of the nitride ceramic raw material powder are different, especially boron nitride has a smaller specific gravity than other nitrides, and the particle shape is flat and special, so a uniform mixed powder can be obtained. Easy wet mixing is preferred.

By the way, in the vapor phase growth method such as the MOVPE method, the GaN crystal grows not only on the substrate of the semiconductor element but also on the susceptor. The GaN crystal grown on the susceptor is peeled off from the susceptor surface due to the revolving motion of the susceptor or the flow of the raw material gas, floats as dust, adheres to the semiconductor element, and becomes a defect of the semiconductor element. In particular, GaN deposited on boron nitride, more specifically, GaN deposited on boron nitride particles having a size of 10 μm or more is more easily separated than GaN deposited on silicon nitride or aluminum nitride, and floats as dust. It becomes easy. Therefore, in the composite sintered body containing boron nitride and at least one of silicon nitride and aluminum nitride, the size of boron nitride particles or aggregated particles containing boron nitride particles exposed on the surface is about several μm at the maximum. It is important to keep it at a low level, but it is difficult to mix for a long time by the dry mixing method.

In wet mixing using a hydrophilic medium such as alcohol, the size of nitride ceramic particles and aggregated particles can be suppressed to several μm. However, moisture contained in a trace amount of alcohol hydrolyzes the nitride ceramic powder. Oxygen increased to lower the thermal conductivity and heat resistance temperature of the sintered body. Alcohol should be dehydrated, but it was difficult to handle and manage because it easily reabsorbs moisture in the air. On the other hand, wet mixing using a lipophilic medium such as liquid fluorocarbon proposed in Patent Document 2 can solve the problem of hydrolysis, but the surface of the nitride ceramic powder is covered with polar groups, so the powder aggregates. Aggregated particles of 10 μm or more were produced. In the wet mixing of Patent Document 3 using a mixed medium of an organic binder, a solvent for the organic binder (alcohols, aromatics, ketones), and a solvent containing a fluorine element (hydrofluorocarbon or hydrochlorofluorocarbon), A nitride composite sintered body having a thickness of about several millimeters may be used. However, when the thickness is 50 mm or more, the organic binder cannot be prevented from remaining, and nitrogen gas is generated by reacting with the nitride during sintering. Cause troubles such as cracks and cracks. Note that the nitride composite sintered body having a thickness of 50 mm or more has a thickness that is convenient for machining a susceptor having a desired shape such as a disk shape, a cylindrical shape, or a gear shape.
JP 2001-44128 A JP-A-5-104015 JP-A-5-254918

An object of the present invention is to produce a nitride composite sintered body suitable for, for example, a susceptor, in which exposure of aggregated particles containing boron nitride particles or boron nitride particles of 10 μm or more is reduced on the surface of the nitride composite sintered body. Is to provide a method.

The present invention relates to a method for firing a mixed powder containing boron nitride powder and at least one of silicon nitride powder and aluminum nitride powder, wherein the mixed powder is obtained by removing the medium from the wet mixture, and the medium is hydrofluorocarbon. And a method for producing a nitride composite sintered body characterized in that alcohol is contained in at least one of hydrofluoroether in an amount of 2 to 10% by mass. In the present invention, the alcohol is preferably at least one selected from ethanol, isopropyl alcohol and t-amyl alcohol, particularly t-amyl alcohol. Especially, it is preferable that alcohol content rate is plus or minus 1 mass% of the azeotropic composition of a medium. The mixed powder preferably contains 20 to 50% by mass of boron nitride powder and 80 to 50% by mass of at least one of silicon nitride powder and aluminum nitride powder.

According to the present invention, the exposure of 10 μm or more boron nitride particles or aggregated particles containing boron nitride particles (hereinafter collectively referred to as “10 μm or more particles”) on the surface of the nitride composite sintered body is reduced. In particular, a method for producing a nitride composite sintered body suitable as a susceptor is provided.

As in the present invention, a composite sintered body manufactured using a mixed powder containing boron nitride and at least one of silicon nitride and aluminum nitride prepared from a wet mixture is compared with a single nitride sintered body. In addition to the excellent basic characteristics of the susceptor, the machinability and the effect of suppressing the exposure of particles of 10 μm or more are remarkable, which makes it possible to manufacture a susceptor with excellent wear resistance and high thermal conductivity. . In particular, a mixed powder containing 20 to 50% by mass of boron nitride and 80 to 50% by mass of at least one of silicon nitride and aluminum nitride is preferable. If the boron nitride is less than 20% by mass, the nitride composite sintered body becomes hard and the workability deteriorates, so that it may be difficult to obtain a member (susceptor) with a precise shape. Moreover, when boron nitride exceeds 50 mass%, since abrasion resistance fall and generation | occurrence | production of dust will become remarkable, there exists a possibility that it may become difficult to use as a susceptor. Note that. For example, a sintering aid such as boron oxide, silicon oxide, aluminum oxide, and yttrium oxide can be contained in the mixed powder at a ratio of 10% by mass or less.

As hydrofluorocarbons and hydrofluoroethers, 1,1,2,2,3,3,4-heptafluorocyclopentane “ZEOLORA” manufactured by Nippon Zeon Co., Ltd., 1,1,1,2,2,3,4 , 5,5,5-decafluoro-3-methoxy-4-trifluoromethyl-pentane, ethyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether, trade name "Novec", 1,1,2, Commercially available products such as “Asahiclin” manufactured by Asahi Glass Co., Ltd., which is 2-tetrafluoroethyl-2,2,2, -trifluoroethyl ether, are used.

The alcohol to be contained in the medium is not particularly limited, but has a boiling point close to that of hydrofluorocarbon, hydrofluoroether, and is compatible with ethanol (C ₂ H ₅ OH), isopropyl alcohol (C ₃ H ₇ OH) and At least one selected from t-amyl alcohol (C ₅ H ₁₁ OH) is preferred. In particular, t-amyl alcohol is preferable from the viewpoint of the dispersibility of the powder, the water content of the medium, and the ease of removal of the medium by distillation. A low molecular weight alcohol such as methanol (CH ₃ OH) has high hydrophilicity, so the medium tends to contain moisture, and a high molecular weight alcohol such as heptyl alcohol (C ₇ H ₁₅ OH) has a boiling point. Since (176 ° C.) becomes high, it becomes difficult to remove the medium.

The content rate in the medium of alcohol is 2-10 mass%. If it is less than 2% by mass, the nitride ceramic powder does not disperse well in the medium, and if it exceeds 10% by mass, the moisture that causes the nitride ceramic powder to hydrolyze even if ordinary moisture management is performed, The medium absorbs from the air.

2-10 mass% of alcohol content rate was calculated | required as follows. That is, three types of nitride ceramic powder {boron nitride powder (trade name “SP” manufactured by Denki Kagaku Kogyo Co., Ltd.), aluminum nitride powder (trade name “H grade” manufactured by Tokuyama Kogyo Co., Ltd.), silicon nitride powder (product manufactured by Denki Kagaku Kogyo Co., Ltd.) 1 g of each of the name “NP-600”) is placed in a 50 mL vial containing a medium of 15 mL of hydrofluoroether (trade name “Novec HFE-7200” manufactured by Sumitomo 3M Limited) or 15 mL of isopropyl alcohol (special grade of Kanto Chemical). After mixing for 1 minute, the mixture was allowed to stand for 1 hour and then the height of the deposited layer was measured. The results are shown in Table 1. In the boron nitride powder or silicon nitride powder, the ratio of the deposition height of both media is 2 or less, and the deposition is relatively dense, and these powders are dispersed in the media regardless of the type of media. The property was good. However, in the case of aluminum nitride powder, the height ratio of the sedimentation layer is 7, and in isopropyl alcohol, the sedimentation layer was dense, but in hydrofluoroether, the sedimentation layer has many gaps. The dispersibility of was poor.

Thus, since it was found that the dispersibility of the nitride ceramic powder in the hydrofluoroether varies depending on the powder type, an alcohol is added to the hydrofluoroether to improve the dispersibility of the aluminum nitride powder in the hydrofluoroether. An attempt was made to mix. That is, the height of the sedimentation layer was measured in the same manner except that the above-described hydrofluoroether and isopropyl alcohol were used and a medium obtained by various mixing with the alcohol content shown in Table 2 was used. As a result, when the alcohol content of the medium is 1% by mass or less, the height of sedimentation is 10 mm or more (sedimentation with many gaps), but when it is 2% by mass or more, the height is less than 10 mm (relatively Dense sedimentation).

On the other hand, in order to evaluate the ease of water absorption of the medium, that is, the ease of hydrolyzing the nitride ceramic powder, 10 mL of water was added to 15 mL of the medium of Table 2 composed of hydrofluoroether and isopropyl alcohol, and after mixing for 1 minute, After standing for one day, the water content of the medium was measured by Karl Fischer titration method of JIS K 0068. As a result, as shown in Table 2, when the alcohol content of the medium exceeded 10% by mass, the water content of the medium became 0.2% by mass or more, and the possibility that the nitride ceramic powder was hydrolyzed was increased. From these things, in this invention, the alcohol content rate in a medium was 2-10 mass%.

When the nitride ceramic powder is hydrolyzed, hydroxide and ammonia are produced. Ammonia vaporizes, but hydroxide remains in the mixed powder as it is, so that the oxygen content in the mixed powder increases. For this reason, the ease of hydrolysis of the nitride ceramic powder can be predicted by the amount of oxygen in the nitride ceramic powder. In the present invention, the amount of oxygen in the nitride ceramic powder is determined by mixing the sample in a medium for a certain period of time (for example, 20 hours) and then removing the medium by distillation or the like, and then, for example, JIS R 1603, Japan Ceramic Society Standard JCRS 105 , 108, etc., can be measured by melting with an inert gas-infrared absorption method.

Even if the alcohol content is in the range of 2 to 10% by mass, it is preferable that the alcohol content is plus or minus 1% by mass of the azeotropic composition. By using such a medium, media such as distillation can be removed. Even after the operation is performed, the change in the alcohol content is small, and further, the content does not change during storage, so that the medium can be easily reused. That is, when the alcohol content deviates significantly from the composition of plus or minus 1% by weight of the azeotropic composition, it is necessary to measure and readjust the alcohol content of the recovered medium each time, and the operation becomes complicated.

In order to produce a medium having an alcohol content of plus or minus 1% by mass of the azeotropic composition, a temperature-composition diagram may be prepared to obtain a composition in which the composition of the gas phase and the liquid phase match. That is, at least one of hydrofluorocarbon and hydrofluoroether whose alcohol concentration is adjusted is placed in a flask or the like equipped with a refluxer, and heated and boiled so that the liquid phase and the gas phase have the same temperature. In this state, the composition of the liquid phase and the gas phase in the flask is analyzed by gas chromatography or the like to create a temperature-composition diagram, and the azeotropic composition is obtained from the composition in which the gas phase and the liquid phase composition match. (Reference: Hideaki Chihara, edited by Michio Tsuji; Physical Chemistry Experimental Method 4th edition, Tokyo Chemical Dojin, (2000)).

The wet mixing of the nitride ceramic raw material powder is performed by using 300 to 800 parts by mass of the medium per 100 parts by mass of the raw material powder and using, for example, a mixing device such as a ball mill, a vibration mill, or a homomixer. The wet mixture is then mixed with a device such as a rotary evaporator or a dryer with a solvent recovery device to produce a mixed powder, which is, for example, a dry press molding method or a cold isostatic press molding method (CIP method). After molding by, for example, normal pressure sintering at 1650 to 2000 ° C. in a non-oxidizing air current such as nitrogen, argon, ammonia, hydrogen, carbon dioxide, or at 1650 to 2000 ° C. under a pressure of 15 to 35 MPa. A nitride ceramic sintered body is manufactured by hot press sintering.

Example 1
Hydrocarbon ether (trade name “NOBEC HFE-7200” manufactured by Sumitomo 3M Co., Ltd.) 95 mass% and medium 700 mL consisting of 5 mass% isopropyl alcohol, boron nitride powder (trade name “SP” manufactured by Denki Kagaku Kogyo Co., Ltd.) 25 mass% 200 g of raw material powder made of aluminum nitride powder (trade name “H grade” made by Tokuyama Co., Ltd., 75 mass%) is placed in a 5 L-container containing 5 kg of alumina balls having a diameter of 5 mm, and mixed for 20 hours in a ball mill (90 revolutions) After that, the medium was evaporated and removed in a dryer (50 ° C., 8 hours) to produce a mixed powder having an oxygen content of 2.5% by mass. Hot press sintering was performed under the conditions of a pressure of 20 MPa and a time of 90 minutes, and a cross section of the obtained composite sintered body was observed with a scanning electron microscope. Particles of μm or more were not observed, and the thermal conductivity according to JIS R 1611 laser flash method was 47 W / m · K.

Example 2
Example 1 except that the medium was changed to a medium composed of 95% by mass of hydrofluoroether (trade name “Asahiclin AE-3000” manufactured by Asahi Glass Co., Ltd.) and 5% by mass of ethanol (Taipei Pharmaceutical Japan Pharmacopoeia). Thus, a composite sintered body was produced. The oxygen content of the mixed powder was 2.7% by mass. Particles of 10 μm or more are not observed in the composite sintered body, and the thermal conductivity is 42 W / m · K.

Example 3
Compound sintering was carried out in the same manner as in Example 1 except that the medium was changed to the commercial name “ZEOLORA HTA”, a commercial product of ZEON Corporation, which is an azeotropic mixture of hydrofluorocarbon and t-amyl alcohol (4.2% by mass). The body was manufactured. The oxygen content of the mixed powder was 2.0% by mass. Particles of 10 μm or more are not observed in the composite sintered body, and the thermal conductivity is 56 W / m · K.

Example 4
A composite sintered body was produced in the same manner as in Example 3 except that the raw material powder was changed to 30% by mass of boron nitride powder, 62% by mass of silicon nitride, 6% by mass of yttrium oxide, and 2% by mass of aluminum oxide. Particles of 10 μm or more are not observed in the composite sintered body, and the thermal conductivity is 45 W / m · K.

Comparative Example 1
A composite sintered body was produced in the same manner as in Example 3 except that the medium was hydrofluoroether alone. The amount of oxygen in the raw material powder was 1.8% by mass. Although the thermal conductivity of the sintered body showed 55 W / m · K, particles of 10 μm or more were observed in the composite sintered body. When used as a member for semiconductor manufacturing equipment such as GaN, there is a concern about the generation of dust.

The nitride composite sintered body manufactured according to the present invention can be used as a member (susceptor) for a semiconductor manufacturing apparatus.

Claims (5)

In a method of firing a mixed powder containing boron nitride powder and at least one of silicon nitride powder and aluminum nitride powder, the mixed powder is obtained by removing the medium from the wet mixture, and the medium is hydrofluorocarbon and hydrofluoroether A method for producing a nitride composite sintered body characterized in that at least one of these comprises alcohol in an amount of 2 to 10% by mass. The production method according to claim 1, wherein the alcohol is at least one selected from ethanol, isopropyl alcohol, and t-amyl alcohol. The production method according to claim 2, wherein the alcohol is t-amyl alcohol. The production method according to claim 1, wherein the alcohol content is 1% by mass or less of the azeotropic composition of the medium. 5. The production according to claim 1, wherein the mixed powder contains 20 to 50% by mass of boron nitride powder and at least one of silicon nitride powder and aluminum nitride powder contains 80 to 50% by mass. Method.