JP4280914B2 - High purity aluminum nitride powder, method for producing the same, and high purity aluminum nitride sintered body - Google Patents

Description

  The present invention relates to a novel high-purity aluminum nitride powder, a method for producing the same, and a high-purity aluminum nitride sintered body.

  Aluminum nitride (AlN) sintered bodies are widely used in various applications such as semiconductor substrates and semiconductor package base materials because of their high thermal conductivity and high electrical insulation. Recently, it is also used as a part for semiconductor manufacturing equipment due to the corrosion resistance and plasma resistance, which are another feature of aluminum nitride.

  These AlN sintered bodies are mainly produced by sintering AlN powder together with a sintering aid as necessary. And the characteristic of the sintered compact obtained by this changes greatly with the characteristic, manufacturing conditions, etc. of the aluminum nitride powder used as a raw material.

  An AlN sintered body used for a semiconductor substrate is required to have high thermal conductivity. Thermal conductivity is reduced by impurities contained in the AlN powder. Specifically, impurities in the AlN powder diffuse into the lattice of AlN during the sintering process and cause lattice defects, thereby reducing the thermal conductivity of the AlN sintered body. In particular, Si, Fe, and oxygen are known to reduce thermal conductivity.

  On the other hand, an AlN sintered body used as a semiconductor manufacturing apparatus component needs to eliminate impurities as much as possible for the purpose of preventing contamination of the silicon wafer. If the AlN sintered body contains a large amount of impurities, the impurities may diffuse on the silicon wafer side. For this reason, the AlN powder used as the raw material of the AlN sintered body needs to reduce impurities including Si.

  However, although the conventional AlN powder has been manufactured with a certain amount of impurities reduced by using a high-purity raw material, it is still not sufficient.

  The AlN powder is industrially produced by a direct nitriding method using metal aluminum powder as a raw material or a reductive nitriding method using alumina as a raw material.

  In the direct nitridation method, AlN powder with few impurities can be obtained by using high-purity aluminum, but there is contamination with impurity metals (particularly Fe) in the subsequent pulverization step. For example, an AlN powder having a total of 5 ppm by weight or less of Ca, K, and Na is disclosed (see, for example, Patent Document 1). However, nothing is mentioned about the reduction of impurities (for example, Fe) other than these components.

  In the reductive nitriding method, by using fine alumina powder, a pulverization step in which impurities are likely to be mixed can be omitted. However, it is industrially difficult to nitrify the entire amount of fine alumina, and unreacted alumina remains as an impurity. In particular, oxygen contained in alumina greatly reduces the thermal conductivity and contaminates the silicon wafer. On the other hand, for example, a method of adding at least one metal or metal oxide selected from the group consisting of alkaline earth metals, yttrium and lanthanum group metals (see, for example, Patent Document 2), adding a calcium compound Methods (for example, see Patent Document 3), methods for adding at least one compound selected from alkaline earth metals and rare earth metals (for example, see Patent Document 4), and the like are disclosed.

  However, in these methods, since additives such as alkaline earth metals remain as impurities, it is difficult to obtain high-purity AlN.

  As a method other than the direct nitriding method and the reductive nitriding method, there is a method in which an organoaluminum compound and ammonia are reacted in a gas phase to obtain a high-purity AlN powder having a total of Fe, Si, Ca, Mg and Ni of 77 ppm by weight or less. Known (for example, see Patent Document 5).

However, it is difficult to handle a large amount of organoaluminum compound and ammonia, and it is difficult to say that it is suitable for production on an industrial scale.
JP 2000-191308 A JP-A-60-65768 JP-A-2-160610 JP-A-5-221618 JP-A-7-33412

  Accordingly, the main object of the present invention is to produce a higher purity aluminum nitride powder on an industrial scale.

  As a result of intensive studies in view of the problems of the prior art, the present inventor has found that the above object can be achieved by producing aluminum nitride powder by a specific process, and has completed the present invention.

That is, the present invention relates to a high purity aluminum nitride powder powder manufacturing how below.

1. A method for producing an aluminum nitride powder from a mixed powder containing an aluminum component by a reduction nitriding method,
(A) The mixed powder is: (1) powder of at least one aluminum-based material of metal aluminum and aluminum compound (excluding aluminum nitride powder), (2) at least one carbon of carbon and carbon compound A powder of a system material (excluding aluminum carbide) and (3) an aluminum nitride powder as a nitriding reaction accelerator,
(B) The mixed powder has a composition of 0.4 to 5 parts by weight (converted to carbon) of carbon-based material and 0.05 to 20 parts by weight of aluminum nitride with respect to 1 part by weight of aluminum-based material (converted to metal aluminum). And
(C) The aluminum-based material is Fe, Ti, K, Na and rare earth elements are each 15 ppm by weight or less, Si and alkaline earth metal is 50 ppm by weight or less,
(D) The reduction nitriding method includes a step of nitriding the mixed powder at 1620 to 1900 ° C. in a nitrogen-containing atmosphere and then decarburizing at 600 to 800 ° C. in an oxidizing atmosphere.
A method for producing a high-purity aluminum nitride powder characterized by the above.

  The high-purity aluminum nitride powder of the present invention has a very low impurity content, and thus can exhibit excellent thermal conductivity as compared with the prior art. For this reason, it can use suitably for the use as which higher thermal conductivity is requested | required.

  Aluminum nitride powder with such characteristics is a material (sintered body) used for semiconductor substrates, semiconductor manufacturing equipment components, etc., as well as fillers such as resin, rubber, and elastomer, and composite materials with metals, glass, ceramics, etc. It is also useful.

  Further, the production method of the present invention makes it possible to efficiently produce the high-purity aluminum nitride powder as described above on an industrial scale.

1. High-purity aluminum nitride powder The high-purity aluminum nitride powder of the present invention has Si and alkaline earth metal of 50 ppm by weight or less, Fe, Ti, K, Na and rare earth elements of 15 ppm by weight and oxygen of 1.5 or less, respectively. It is characterized by not more than wt% and carbon not more than 0.15 wt%.

  The Si content is 50 ppm by weight or less, preferably 35 ppm by weight or less. When Si content exceeds 50 weight ppm, there exists a possibility that the heat conductivity of the sintered compact obtained from this invention powder may fall. The lower limit of the Si content is not limited as long as it can be produced, but it may be about 0.01 ppm by weight in consideration of economy and the like.

  The content of alkaline earth metal (in particular, at least one of Be, Mg, Ca, Ba and Sr) is 50 ppm by weight or less, preferably 20 ppm by weight or less. When alkaline earth metal content exceeds 50 weight ppm, there exists a possibility that the heat conductivity of the sintered compact obtained from this invention powder may fall. Further, when the sintered body is used as a semiconductor manufacturing apparatus component, the silicon wafer may be contaminated with an alkaline earth metal. The lower limit of the alkaline earth metal content is not limited as long as it can be produced, but it may be about 0.01 ppm by weight in consideration of economy and the like.

  Rare earth elements (especially, at least one of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), Fe, Ti, K and Na. Each content is 15 ppm by weight or less, preferably 10 ppm by weight or less. When the content of these components exceeds 15 ppm by weight, the thermal conductivity of the sintered body obtained from the powder of the present invention may be reduced. Further, when the sintered body is used as a semiconductor manufacturing apparatus component, the silicon wafer may be contaminated by these elements. In addition, although the lower limit of these content is not restrict | limited as long as manufacture is possible, if it considers economical efficiency etc., what is necessary is just to be about 0.01 weight ppm of each.

  The oxygen content is 1.5% by weight or less, preferably 1.2% by weight or less. When oxygen content exceeds 1.5 weight%, there exists a possibility that the heat conductivity of the sintered compact obtained from this invention powder may fall. The lower limit of the oxygen content is not limited as long as it can be manufactured, but it may be about 0.3% by weight in consideration of economy and the like.

  The carbon content is 0.15% by weight or less, preferably 0.10% by weight or less. When carbon content exceeds 0.15 weight%, there exists a possibility that the heat conductivity of the sintered compact obtained from this invention powder may fall. Moreover, there exists a possibility that the color tone of the obtained sintered compact may become black. The lower limit of the carbon content is not limited as long as it can be produced, but it may be about 0.01% by weight in consideration of economy and the like.

  The aluminum nitride powder of the present invention may contain other inevitable impurities (hereinafter simply referred to as “inevitable impurities”) as long as the effect thereof is not impaired. It is desirable that it is 300 ppm by weight or less.

The average particle size of the aluminum nitride powder of the present invention is not particularly limited, and may be appropriately changed from the range of usually 0.5 to 200 μm according to the purpose of use. The shape of the powder is not particularly limited, and may be any of a spherical shape, a needle shape, a flat shape, a plate shape, a rod shape, a teardrop shape, an indefinite shape, and the like.
2. Production method of high-purity aluminum nitride powder The high-purity aluminum nitride powder of the present invention is, for example, a method of producing an aluminum nitride powder from a mixed powder containing an aluminum component by a reduction nitriding method. It can be obtained by a method for producing a high-purity aluminum nitride powder characterized by being contained in the mixed powder.

  The mixed powder should just contain an aluminum component, Preferably what contains at least 1 type of aluminum type material (however, except aluminum nitride) of metal aluminum and an aluminum compound can be used conveniently. Aluminum-based materials include Fe, Ti, K, Na and rare earth elements of 15 ppm by weight or less, Si and alkaline earth metals of 50 ppm by weight or less, respectively, and change to oxides of aluminum at the nitriding temperature If it is, it will not specifically limit.

  As the metallic aluminum, those having an Al purity of 99.8% or more can be suitably used. Examples of the aluminum compound include aluminum oxide (alumina), hydroxide, halide, inorganic acid salt (sulfate, nitrate, carbonate and the like), aluminum organic compound (aluminum alkoxide and the like), and the like. These can be used alone or in combination of two or more. Among these, in order to obtain high reactivity, it is preferable to select an aluminum compound having higher reactivity. For example, when alumina is used as the aluminum compound, it is more preferable to use γ-alumina than α-alumina.

  The aluminum-based material is desirably used in powder form. The particle size in this case may be appropriately set according to the type of compound to be used. However, when high reactivity is desired, it is preferable to use a powder having a particle size as small as possible. In general, an aluminum compound powder having an average particle size of 30 μm or less may be used.

  The mixed powder may contain a reducing agent. As the reducing agent, at least one carbon-based material (except aluminum carbide) of carbon and carbon compounds can be suitably used. The carbon-based material changes to carbon at the nitriding temperature, and Fe, Ti, K, Na and rare earth elements are each 15 ppm by weight or less, and Si and alkaline earth metal are each 50 ppm by weight or less. If there is no particular limitation. Examples of carbon include graphite, carbon black, acetylene black, and amorphous carbon. Examples of the carbon compound include resins such as phenol resin and polyacrylonitrile. These can be used alone or in combination of two or more.

  The reducing agent is preferably used as a powder. The particle size in this case can be determined as appropriate according to the type of reducing agent used. For example, when a carbon-based material is used, the average particle size is preferably 1 μm or less.

  The amount of reducing agent used varies depending on the type of aluminum component used, nitriding conditions, etc., but is usually 0.4 to 5 parts by weight (carbon equivalent. The same applies hereinafter) relative to 1 part by weight of aluminum-based material (metal aluminum equivalent). ), In particular, 0.6 to 3 parts by weight is desirable. If the amount is less than 0.4 parts by weight, the reduction reaction (that is, nitriding reaction) of the aluminum compound becomes insufficient, the oxygen content increases, and the thermal conductivity of the resulting AlN sintered body may be lowered. Moreover, when it exceeds 5 weight part, there exists a possibility that much time may be required for a decarburization process, and there exists a possibility that carbon may remain | survive as an impurity.

  The aluminum nitride powder used as the nitriding reaction accelerator is not limited in its kind, and any product obtained by any manufacturing method can be used, and a commercially available product can also be used. Such a powder, the composition of the resulting aluminum nitride powder is such that Fe, Ti, K, Na and rare earth elements are each 15 ppm by weight or less, and Si and alkaline earth metal are each 50 ppm by weight or less. May be selected as appropriate.

  The particle size of the aluminum nitride powder is not particularly limited, but it is generally desirable to use an aluminum nitride powder having an average particle size of 10 μm or less.

  The amount of aluminum nitride powder used can be appropriately determined depending on the composition of the mixed powder to be used, but is usually 0.05 to 20 parts by weight, particularly 0.1 to 1 part by weight of aluminum-based material (in terms of metallic aluminum). It is desirable to set it to 10 weight part. Within this range, the composition of the obtained aluminum nitride powder may be adjusted so that Fe, Ti, K, Na and rare earth elements are each 15 ppm by weight or less, and Si and alkaline earth metal are each 50 ppm by weight or less. it can. If the amount is less than 0.05 parts by weight, the reduction reaction (that is, nitriding reaction) of the aluminum-based material becomes insufficient, the oxygen content increases, and the thermal conductivity of the resulting AlN sintered body may be lowered. On the other hand, when the amount exceeds 20 parts by weight, the amount of the aluminum-based material is relatively decreased, the productivity may be lowered, and the amount of impurities may be increased.

  By mixing these uniformly, a mixed powder can be obtained. The mixing may be either dry or wet, but is preferably dry mixing from the viewpoint that productivity can be further improved. For mixing, a known mixing apparatus such as a ball mill, a vibration mill, or an attritor can be used. Among these, it is desirable to use a container and a ball made of high-purity alumina or plastic in that impurities can be avoided from mixing members as much as possible.

  Next, the mixed powder is processed by a reduction nitriding method. For the reduction nitriding method, the conditions of a known reduction nitriding method can be employed. In particular, in the present invention, the mixed powder is preferably nitrided at 1600 to 1900 ° C. in a nitrogen-containing atmosphere and then decarburized at 600 to 800 ° C. in an oxidizing atmosphere. By treating under the above conditions, a high-purity aluminum nitride powder with a controlled amount of impurities can be obtained more reliably.

  The nitriding treatment is preferably performed at 1600 to 1900 ° C. (particularly 1650 to 1850 ° C.) in a nitrogen-containing atmosphere. The treatment time varies depending on the treatment temperature and the like, but is usually about 3 to 10 hours. The nitrogen-containing atmosphere includes not only a nitrogen gas atmosphere but also an atmosphere in which nitrogen gas is diluted with an inert gas (helium gas, argon gas, etc.).

The decarburization treatment is preferably performed at 600 to 800 ° C. (particularly 650 to 750 ° C.) in an oxidizing atmosphere. The treatment time varies depending on the treatment temperature and the like, but is usually about 2 to 24 hours. The oxidizing atmosphere includes not only the atmosphere or oxygen gas atmosphere but also an atmosphere obtained by diluting these gases with an inert gas (helium gas, argon gas, etc.).
3. High purity aluminum nitride sintered body The high purity aluminum nitride sintered body of the present invention is obtained by sintering the high purity aluminum nitride powder of the present invention. The sintering temperature is usually in the range of about 1650 to 2100 ° C. The sintering atmosphere is preferably a nitrogen atmosphere. Also, the sintering method is not limited, and any of normal pressure sintering and pressure sintering can be employed.

  In the present invention, high-purity aluminum nitride powder can be formed into a desired shape prior to sintering. The molding method may be a known molding method such as a press molding method, an extrusion molding method, or a CIP method. In this case, a known binder (acrylic binder, polyvinyl alcohol binder, polyvinyl butyral binder, etc.) and an organic solvent (isopropyl alcohol, ethanol, methanol, butanol, hexane, etc.) may be added as necessary. Further, the raw material powder can be granulated in advance before molding. For example, a slurry made of high-purity aluminum nitride powder may be prepared and granulated using this slurry. The granulation method and the like can be performed according to a known method.

Examples and comparative examples will be shown below to clarify the features of the present invention. However, the scope of the present invention is not limited to these examples. Each physical property was measured as follows.
(1) Carbon content Measured by combustion in an oxygen stream-infrared absorption method.
(2) Oxygen amount Measured by dissolution in an inert gas-infrared absorption method.
(3) Nitrogen amount Measured by dissolution in an inert gas-heat conduction method.
(4) Metal impurity content Measured by ICP emission spectrometry or flame analysis.
(5) Thermal conductivity It measured by the laser flash method.

Examples 1-11
(1) Production of aluminum nitride powder Using the aluminum-based material, carbon-based material, and nitriding reaction accelerator (additive) shown in Table 1, dry mixing was performed for 20 minutes with a vibration mill with the composition shown in Table 2. The obtained mixed powder was transferred to a high-purity graphite crucible and subjected to nitriding by heating at a nitriding temperature shown in Table 2 for 5 hours while supplying nitrogen gas at 3 liters / minute. The reaction product after the nitriding treatment was decarburized by heating in the atmosphere at the temperature shown in Table 2 for 8 hours.

When the obtained powder was analyzed by X-ray diffraction, the pattern showed only the diffraction pattern of AlN, and no pattern of other aluminum compounds was observed. Further, the carbon content, oxygen content, nitrogen content and metal impurity content of the powder were measured. The results are shown in Table 3.
(2) Manufacture of sintered body A A sintered body was manufactured using each aluminum nitride powder obtained in (1) above. A graphite die (diameter 20 mm) coated with boron nitride (BN) is filled with 2 g of aluminum nitride powder, and pressure-fired under a pressure of 9.8 MPa in nitrogen gas at 2000 ° C. for 3 hours using a high-frequency induction heating furnace. Yui was carried out. The thermal conductivity of the obtained sintered body was measured. The results are shown in Table 4. The values shown in Table 4 are shown as a ratio to Comparative Example 13 (the same applies hereinafter).
(3) Production of sintered body B 100 parts by weight of the aluminum nitride powder obtained in (1) above, 5 parts by weight of Y 2 O 3 (sintering aid) and 2 parts by weight of an acrylic binder (binder) were mixed with an organic solvent (isopropyl alcohol). ) 50 parts by weight was mixed with a wet ball mill, and the resulting slurry was granulated and dried to obtain granules for molding. The granules for molding were formed into pellets by a uniaxial press, and then further pressed by the CIP method. The obtained molded body was degreased at 450 ° C., and then sintered at 1800 ° C. for 3 hours in a nitrogen atmosphere to obtain a sintered body. The thermal conductivity of the obtained sintered body was measured. The results are shown in Table 4.

比較例１、２、４、７、８及び１０
表２に示す組成としたほかは、実施例１と同様にして粉末及び焼結体を製造した。各粉末についてＸ線回折分析したところ、いずれの回折パターンにもＡｌＮの回折ピークとともにアルミニウム酸化物及びアルミニウム酸窒化物（ＡｌＯＮ）の回折ピークも認められた。各粉末の、酸素量、窒素量及び金属不純物含有量を表３に示す。また、焼結体の熱伝導率を表４に示す。

Comparative Examples 1, 2, 4, 7, 8, and 10
A powder and a sintered body were produced in the same manner as in Example 1 except that the composition shown in Table 2 was used. As a result of X-ray diffraction analysis of each powder, the diffraction peak of aluminum oxide and aluminum oxynitride (AlON) was observed in each diffraction pattern as well as the diffraction peak of AlN. Table 3 shows the oxygen content, nitrogen content and metal impurity content of each powder. Table 4 shows the thermal conductivity of the sintered body.

Comparative Examples 3, 5, 6, 9 and 11
A powder and a sintered body were produced in the same manner as in Example 1 except that the composition shown in Table 2 was used. When X-ray diffraction analysis was performed on each powder, only the diffraction peak of AlN was observed in any diffraction pattern, and there was no diffraction peak of the aluminum compound. Table 3 shows the oxygen content, nitrogen content and metal impurity content of the powder. Table 4 shows the thermal conductivity of the sintered body.

Comparative Example 12
Table 3 shows the oxygen content, the nitrogen content, and the metal impurity content of commercially available high-purity AlN powder (product number H grade, manufactured by Tokuyama Corporation) synthesized by the reduction nitriding method. Table 4 shows the thermal conductivity of a sintered body produced using this powder in the same manner as in Example 1.

Comparative Example 13
Table 3 shows the oxygen content, the nitrogen content, and the metal impurity content of commercially available high-purity AlN powder (part number UF grade, manufactured by Toyo Aluminum Co., Ltd.) synthesized by the direct nitriding method. Table 4 shows the thermal conductivity of a sintered body produced using this powder in the same manner as in Example 1.

Claims (1)

A method for producing an aluminum nitride powder from a mixed powder containing an aluminum component by a reduction nitriding method,
(A) The mixed powder is: (1) powder of at least one aluminum-based material of metal aluminum and aluminum compound (excluding aluminum nitride powder), (2) at least one carbon of carbon and carbon compound A powder of a system material (excluding aluminum carbide) and (3) an aluminum nitride powder as a nitriding reaction accelerator,
(B) The mixed powder has a composition of 0.4 to 5 parts by weight (converted to carbon) of carbon-based material and 0.05 to 20 parts by weight of aluminum nitride with respect to 1 part by weight of aluminum-based material (converted to metal aluminum). And
(C) The aluminum-based material is Fe, Ti, K, Na and rare earth elements are each 15 ppm by weight or less, Si and alkaline earth metal is 50 ppm by weight or less,
(D) The reduction nitriding method includes a step of nitriding the mixed powder at 1620 to 1900 ° C. in a nitrogen-containing atmosphere and then decarburizing at 600 to 800 ° C. in an oxidizing atmosphere.
A method for producing a high-purity aluminum nitride powder characterized by the above.