JPH0230608A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To efficiently and inexpensively produce a highly pure aluminum nitride powder for highly heat-conductive ceramic base boards at a low temperature by adding a nitriding reaction catalyst to an aluminum-containing compound and subsequently calcining the mixture in a nitrogen-containing non-oxidizable atmosphere. CONSTITUTION:An Al-containing compound such as Al2(SO4)3 is mixed with preferably a carbon compound e.g. a saccharide such as glucose or a cellulose derivative such as methyl cellulose and catalyst components, preferably a Ca salt, Y salt and lanthanide group element salt, which accelerate a nitriding reaction on a calcination reaction and have a decarbonization action. These compound are used in forms of water-soluble salts and a powder obtained by removing water from the aqueous solution of a mixture of the components is calcined at >=900 deg.C, preferably at 1,200-1,800 deg.C in a nitrogen-containing non- oxidizable atmosphere to provide an AlN powder. The catalyst components each is preferably added in an amount of approximately 0.3-7.0wt.% converted into the non-calcined oxide on the weight of the AlN as a standard.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for producing aluminum nitride powder, which is used, for example, to produce highly thermally conductive ceramic substrates.

[Conventional technology]

BACKGROUND OF THE INVENTION As semiconductor devices such as ICs have become more highly integrated and have more power, electrical insulating materials with good heat dissipation properties have become required. In response to this demand, various highly thermally conductive substrates have been proposed. Among them, aluminum nitride ceramic substrates are particularly being put into practical use because they are excellent in terms of high thermal conductivity, low thermal expansion, high electrical insulation, and the like.

However, this aluminum nitride ceramic substrate has
The disadvantage is that it is expensive. Reasons for the high price include, in particular, the high cost of aluminum nitride powder as a raw material and the high temperature required for sintering.

Conventionally, aluminum nitride powder has been produced by a carbon reduction method in which a mixture of aluminum oxide aluminum and carbon powder is fired in a nitrogen atmosphere, a direct nitriding method in which metallic aluminum is fired in a nitrogen or ammonia gas stream, and the like.

However, with the above-mentioned direct nitriding method of metallic aluminum, it is difficult to obtain aluminum nitride powder with high purity and small particle size.On the other hand, with the carbon reduction method of aluminum oxide, the reaction requires high temperature and the raw material price is high. There were problems such as the high cost of aluminum nitride due to the high cost of aluminum nitride.

Therefore, as an improvement to the carbon reduction method of alumina, a method has been proposed in which aluminum nitride powder is produced by calcining a precipitate obtained from a suspension containing an aluminum source and carbon powder (Tokuko Showa). 61-26485), in this method, the aluminum source and the carbon powder are only mixed in a suspended state, but not in the molecular order, so aluminum nitride is not produced from the resulting precipitate. Since the reaction requires a high temperature and the firing temperature must be increased, there remain problems such as high manufacturing costs.

Therefore, the present applicant prepared an aqueous solution of an aluminum source, a carbon source, and other raw material components, removed water from this aqueous solution, and fired the resulting powder in a non-oxidizing atmosphere containing nitrogen. He developed a method for producing aluminum powder and previously filed patent applications such as Japanese Patent Application No. 199742/1986.

According to this manufacturing method, each raw material component is mixed in an aqueous solution on a molecular order, so each raw material component is homogeneously mixed in the powder obtained by removing water from this aqueous solution, and the firing process The reaction for producing aluminum nitride is carried out well. Therefore, it is possible to obtain fine-grained aluminum nitride powder with extremely high purity, and the firing temperature can also be relatively low, resulting in excellent effects such as reducing manufacturing costs.

[Problem to be solved by the invention]

However, after examining the above method in more detail,
It has been found that there is still room for further improvement in the purity of aluminum nitride obtained by this method. In other words, the purity of this aluminum nitride determines the thermal conductivity of the resulting aluminum nitride ceramic substrate. There is a need for an aluminum nitride ceramic substrate with excellent thermal conductivity.

In view of the above circumstances, it is an object of the present invention to provide a method for producing aluminum nitride powder of even higher purity at low temperatures, efficiently, and at low cost.

[Means to solve the problem]

As a result of repeated studies to solve the above problems, we found that it is sufficient to use a catalyst component that promotes the nitriding reaction of the raw material aluminum-containing compound during sintering, and that some of these catalyst components have the ability to act as a sintering aid. They discovered that there are some products that also have the following properties, and completed this invention.

Therefore, the present invention provides a method for producing aluminum nitride powder by firing a raw material component of aluminum nitride containing at least an aluminum-containing compound in a non-oxidizing atmosphere containing nitrogen, which promotes the nitriding reaction during the firing. A catalyst component is added to the aluminum nitride raw material component.

As the catalyst component, it is preferable to use at least one of a calcium salt, a, thorium salt, and a salt of a lanthanide group element.

Furthermore, a water-soluble compound is used as a raw material component of aluminum nitride, and a water-soluble compound that also has performance as a sintering aid is used as a catalyst component, and the powder obtained by removing water from an aqueous solution containing these compounds is fired. Aluminum nitride powder can also be produced by this method.

[Function] If a catalyst component that has the effect of accelerating the nitriding reaction during calcination and increasing the reaction rate is added to the raw material components in advance, the nitriding rate can be improved and aluminum nitride of higher purity can be obtained. can.

In addition to promoting the nitriding reaction, many of these catalyst components also have the effect of promoting the decarbonization reaction of aluminum nitride after firing. Promotion of this decarbonization reaction means increasing the decarbonization efficiency (reducing the amount of residual carbon) or lowering the decarbonization temperature (by about 50 to 100°C) when there is residual carbon in the aluminum nitride powder after firing. It means to let. Lowering this decarbonization temperature prevents oxidation of aluminum nitride during the decarbonization process, which further increases the purity of the obtained aluminum nitride and ultimately improves the purity of aluminum nitride (aluminum nitride ceramics). This leads to the effect of increasing thermal conductivity.

Here, calcium salts, yttrium salts, and salts of lanthanide group elements are all good examples that exhibit particularly excellent two catalytic actions.

Furthermore, by selecting a catalyst component that also has the performance as a sintering aid, a highly purified aluminum nitride powder containing a component that is both a catalyst and a sintering aid can be obtained. This sintering aid is used to promote the sintering of aluminum nitride, which is difficult to sinter, and to create a dense sintered body when aluminum nitride powder is fired to produce aluminum nitride ceramics for use as insulating substrates. It is an additive needed to obtain That is, the sintering aid reacts with aluminum nitride to produce a liquid phase, which facilitates the sintering of aluminum nitride, and plays the role of keeping oxygen and the like that inhibit heat dissipation in the grain boundaries.

Here, if a water-soluble catalyst component that also has the performance as a sintering aid is selected and added to the aqueous solution containing the aluminum nitride raw material component, the same catalyst component as the aluminum nitride raw material component can be added. This means that they are evenly dispersed and mixed on the molecular order. Therefore, the mixed powder obtained by removing water from this aqueous solution contains the catalyst component in a homogeneous state, and the aluminum nitride powder obtained by firing the mixed powder also contains the catalyst component (catalyst component (especially when a large amount of sintering agent is used), the sintering aid component is homogeneously contained at the same time as the catalyst component. the result,
The obtained aluminum nitride powder has the advantage that it can be used as it is for the sintering production of aluminum nitride ceramics without the need to add or mix sintering aid powder as in the conventional method. can also be resolved.

That is, conventionally, when producing "aluminum quaternide ceramics" from aluminum nitride powder, solid powder Yt Oi, Ca O, etc. were used as sintering aids, and after stirring and mixing these with aluminum nitride powder,
Although firing was carried out using an appropriate process, there was a problem in that it was difficult to homogeneously mix the sintering aid powder and aluminum nitride powder by simply stirring and mixing them. If the sintering aid and aluminum nitride are not homogeneously mixed, the sintering aid will not work effectively, and the aluminum nitride may not be sintered sufficiently, and the quality and performance of the manufactured aluminum nitride ceramics will deteriorate. This mixing operation is very troublesome and requires a mixing device for that purpose, which also causes an increase in the manufacturing cost of aluminum nitride ceramics.

〔Example〕

Next, embodiments of the present invention will be described in detail.

First, as raw material components for aluminum nitride, an aluminum-containing compound is essential, and if necessary, a carbon-containing compound and/or a nitrogen-containing compound, etc. are used. In other words, when the aluminum-containing compound contains a carbon element or a nitrogen element, it is not necessary to use the carbon-containing compound or the nitrogen-containing compound together.

The aluminum-containing compound serves as a source of aluminum, which is the main component of aluminum nitride. Therefore, as long as it is a compound containing aluminum, there are no particular limitations, such as alumina 9 aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum lactate.

Good examples include aluminum polynuclear complexes and aluminum alkoxides. Examples of the aluminum polynuclear complex include basic aluminum chloride, basic aluminum lactate, and basic aluminum nitrate. As the aluminum alkoxide, aliphatic alkoxides having 10 or less carbon atoms, such as aluminum methoxide, 5-aluminum ethoxide, aluminum proboquine, aluminum isopropoxide, and aluminum butoxide, are preferably used, but other alkoxides can be used as well. These aluminum-containing compounds may be used alone or in combination.

The carbon-containing compound functions to remove the oxygen element contained in the mixed powder of the aluminum-containing compound and the like in the form of co and co□ in the aluminum nitride production reaction in the firing process.

Therefore, it is particularly important when the aluminum-containing compound contains a large amount of oxygen element. The carbon-containing compound may be any compound containing a large amount of carbon element, and specifically includes sugars such as glucose, cellulose derivatives of methylcellulose sugar, lignin, polyethylene oxide, polyvinyl alcohol, water-soluble acrylic compounds, Carbon black and the like can be suitably used. These can be used alone or in combination.

The nitrogen-containing compound has the effect that by including a nitrogen source in the mixed powder during the firing process, a reducing atmosphere due to nitrogen is locally formed inside the mixed powder and promotes the nitridation of aluminum from inside the mixed powder. Fulfill. Note that since the firing atmosphere also contains nitrogen, aluminum nitride can be produced even without a nitrogen-containing compound.

The nitrogen-containing compound may be any compound containing nitrogen, and is not particularly limited, for example, urea.

Good examples include water-soluble amino acids such as melamine and glycine, carbonyl hydrazide, and ethylene diamine.
These may be used alone or in combination.

Next, regarding the catalyst component, any catalyst component may be used as long as it has the effect of promoting the nitriding reaction of the aluminum-containing compound during firing. Furthermore, it is desirable that it also has the effect of promoting the decarbonization reaction of aluminum nitride after firing.
In particular, compounds (salts) containing calcium, yttrium, and lanthanide group elements can be preferably used.

However, it is not limited to these, and for example, C
It is similarly preferable to use a compound containing an alkaline earth metal other than a or a metal of the Ma group other than Y. Specifically, calcium salts include calcium nitrate, calcium carbonate, calcium oxide, calcium lactate, calcium acetate, calcium chloride, and the like. Yttrium salts include yttrium nitrate, yttrium acetate, yttrium oxide, yttrium lactate, yttrium chloride, etc.
Examples of salts of lanthanide group elements include lanthanum chloride and the like. These catalyst components may be used alone or in combination.

Some of the catalyst components in this invention also have performance as a sintering aid. Therefore, by using such a catalyst component, it is possible to obtain an aluminum nitride powder containing a sintering aid component. However, in that case, as described below, it should be added in a larger amount than when used as a catalyst. In other words, when used as a catalyst, it is sufficient to add a so-called catalytic amount, but in order to use it as a sintering aid at the same time as a catalyst and leave the sintering aid component in the aluminum nitride powder, it is necessary to evaporate and disappear during firing. It is necessary to set a large amount including minutes.

The amount of the catalyst component added above should be determined so that it is expected to have only a catalytic effect, or it also has the performance as a sintering aid, so that the same component is left behind after firing. It depends on whether or not, etc.
Depending on the usage situation, it may be set appropriately so as to obtain the most excellent effect. Specifically, if the lower limit is the amount of catalyst and the upper limit is the amount left as a sintering aid, for example,
Based on the aluminum nitride powder to be synthesized, it is preferably about 0.3 to 7.0% by weight of each oxide before firing. However, depending on the type of catalyst component, there is a more preferable usage range, and in the case of calcium salt, it should be 0.3 to 4.0% by weight in terms of CaO, based on the synthesized AIN powder. is even more preferable. In the case of yttrium salts and salts of lanthanide group elements, 1.0 to 7.0 on the same basis in terms of each oxide.
It is more preferable if it is expressed as % by weight. Note that these amounts are the amounts that are blended with the raw materials, and some of the catalyst components evaporate during firing, so the amount that actually remains with aluminum nitride after firing is less than the above amounts. Become.

Aluminum nitride powder can be obtained by firing a mixed powder consisting of the above raw material components and catalyst components in a non-oxidizing atmosphere containing nitrogen, but if each of the above components is water-soluble. It is preferable that these are mixed as an aqueous solution, and then the water is removed and the resulting mixed powder is fired.

In other words, when mixed in an aqueous solution, each component is homogeneously mixed on a molecular order, and as a result, a mixed powder in which each component is homogeneously mixed is obtained, which further enhances the catalytic effect and promotes the nitriding reaction. It works effectively. As the moisture removal means, ordinary moisture removal means used in conventional ceramic material manufacturing methods can be appropriately employed.

In particular, this aqueous solution preparation is important when the catalyst component is a water-soluble compound that also has the performance as a sintering aid as described above. can obtain good aluminum nitride powder,
In producing aluminum nitride ceramics, the -layer can be a preferred raw material.

The firing conditions are not particularly limited, but for example, the temperature is 900°C or higher, preferably 1200°C or higher.
-1800°C is selected. Further, as the non-oxidizing atmosphere, in addition to argon, -carbon oxide, and nitrogen gas, a gas containing nitrogen such as ammonia, a mixed gas of nitrogen and hydrogen, etc. can also be used. In this firing process, nitrogen and aluminum are combined to produce aluminum nitride, and impurities such as oxygen elements are burned off.

After the above firing step, if there is residual carbon in the aluminum nitride powder, it can be removed by heat treatment in an oxidizing atmosphere at 500 to 700°C.

In addition to the above-mentioned steps, the manufacturing method of the present invention is not limited to the above examples, as other steps used in ordinary ceramic powder manufacturing methods can be added as necessary.

Below, more detailed examples of the present invention will be described together with comparative examples. First, we will describe the different types when focusing on catalytic performance. All of the catalyst components used also have performance as sintering aids, and by adjusting the amount added, sintering aids can be Easily sinterable aluminum nitride powder that can be sintered without the addition of agents is obtained.

Example 1 - Calcium nitrate was added as a catalyst component to an aqueous solution of aluminum sulfate and methylcellulose mixed at a C/Al (element blending molar ratio) of 3.0.
The mixture was mixed at a concentration of 0.5% by weight in terms of CaO based on the IN powder. Water was evaporated from the resulting aqueous solution to obtain a mixed powder, which was then calcined at 1600° C. for 5 hours in a nitrogen stream to obtain aluminum nitride powder. Furthermore, the obtained aluminum nitride powder was heat treated in air at 600° C. for 6 hours to remove unreacted residual carbon.

After molding the above aluminum nitride powder in a mold, 1
It was fired at 700°C for 6 hours to obtain an aluminum nitride sintered body (ceramics).

Example 2 - Carbon black on α-alumina, C/A I of 3.
Calcium chloride was added to the above Example 1.
Similarly, the amount of CaO was 0.5% by weight based on the AIN powder to be synthesized. Thereafter, aluminum nitride powder was obtained by firing in the same manner as in Example 1, and an aluminum nitride sintered body was further produced.

Example 3 - A solution of aluminum propoxide dispersed in isopropyl alcohol was added with a C/AI of 3.0 and 0.5% by weight in terms of CaO based on the AIN powder to be synthesized. A mixed aqueous solution of glucose and calcium nitrate was added and thoroughly stirred. Note that the amount of glucose added was calculated excluding the amount of carbon contained in aluminum propoxide. After water was removed from this mixed solution to obtain a mixed powder, it was fired in the same manner as in Example 1 to obtain aluminum nitride powder, and further an aluminum nitride sintered body was manufactured.

Examples 4 to 9 Aluminum nitride powder was obtained by preparing an aqueous solution, removing moisture, and firing in the same manner as in Example 1 using the raw material components and catalyst components shown in Table 1. Further, when the produced aluminum nitride powder contained a catalyst component in an amount that could be expected to function as a sintering aid, an aluminum nitride sintered body was produced in the same manner as in Example 1 above. Note that the amount of the catalyst component added was determined based on the synthesized AIN powder, converted into Y and O□ in the case of yttrium salt, and Lago in the case of lanthanum salt. Furthermore, in Example 5, the amount of glucose added was calculated in consideration of the amount of carbon contained in basic aluminum lactate.

- Comparative Example - Aluminum nitride powder was produced in the same manner as in Example 1 using the raw material components shown in Table 1, except that no catalyst component was added.

For the obtained aluminum nitride powders of Examples and Comparative Examples, the nitridation rate and carbon residual amount were determined, and the density and thermal conductivity of the sintered bodies were measured.

The above results are also shown in Table 1.

As shown in Table 1, compared to the comparative example, in the example, high purity aluminum nitride powder with a high nitriding rate and a small amount of residual carbon was obtained, and the amount of the catalyst component added is considered to be the so-called catalytic amount. It was confirmed that even a small amount is sufficiently effective. In addition, if this aluminum nitride powder contains a sufficient amount of catalyst components, ie, sintering aids,
An aluminum nitride sintered body with very low thermal conductivity was produced from the same powder.

Next, as Examples 10 to 15, specific examples will be shown in which the performance as a sintering aid is also expected from the catalyst component. All Examples were carried out by preparing an aqueous solution using each raw material shown in Table 2, and the firing conditions were as follows:
The firing temperature was 1600° C. and the firing time was 6 hours in a nitrogen atmosphere.

Similarly, Table 2 shows the nitridation rate and particle size of the produced aluminum nitride powder.

As shown in Table 2, aluminum nitride fine particles with a high nitridation rate can be obtained from these examples as well, and the aluminum nitride powder can be prepared by mixing a sintering aid in the conventional manner. It can be used as is for the sintering and exposure production of aluminum nitride ceramics.

〔Effect of the invention〕

According to the method for producing aluminum nitride powder according to the present invention as described above, the nitriding reaction is promoted by the action of the catalyst component, and depending on the type of catalyst component (in many cases)
Since decarbonization after firing is also facilitated, highly pure aluminum nitride powder can be produced at low temperatures.

Furthermore, by using a water-soluble compound that also has the performance as a sintering aid as a catalyst component and mixing it with the raw material component of aluminum nitride in an aqueous solution state, both of them can be made homogeneous on the molecular order. By mixing, it is possible to finally obtain a high purity aluminum nitride powder in which the sintering aid components are homogeneously mixed. Therefore, unlike the conventional method for producing aluminum nitride ceramics, the step of mixing the fired aluminum nitride powder and the solid powdered sintering aid one by one is not necessary. Moreover, as a result of the homogeneous dispersion mixing on the molecular order, the aluminum nitride ceramics can be sintered well, and ceramic products with excellent quality and performance can be manufactured.

Agent: Patent Attorney Takehiko Matsumoto

Claims (1)

[Claims] 1. A method for producing aluminum nitride powder by firing raw material components of aluminum nitride containing at least an aluminum-containing compound in a non-oxidizing atmosphere containing nitrogen, in which the nitriding reaction during the firing is promoted. A method for producing aluminum nitride powder, characterized in that a catalyst component is added to the aluminum nitride raw material component. 2. The method for producing aluminum nitride powder according to claim 1, wherein at least one of a calcium salt, a yttrium salt, and a salt of a lanthanide group element is used as the catalyst component. 3. Using a water-soluble compound as a raw material component of aluminum nitride and also using a water-soluble compound that also has performance as a sintering aid as a catalyst component, and firing the powder obtained by removing water from an aqueous solution containing these compounds. 3. The method for producing aluminum nitride powder according to claim 1 or 2.