JPH062564B2 - Manufacturing method of aluminum nitride powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride powder used for producing, for example, a ceramic substrate with high thermal conductivity.

[Conventional technology]

With the progress of higher integration and higher power consumption of semiconductor elements represented by ICs and the like, along with this, electric insulating materials having good heat dissipation have been required. In response to this, various high thermal conductive substrates have been proposed. Among them, in particular, aluminum nitride ceramic substrates are being put to practical use because they are excellent in high thermal conductivity, low thermal expansion property, high electrical insulating property and the like.

However, in this aluminum nitride ceramic substrate,
It has the drawback of being expensive. The reason for the high price is that aluminum nitride powder as a raw material is expensive and that sintering requires high temperature.

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

However, it is difficult to obtain a high-purity aluminum nitride powder having a small particle size by the above-mentioned direct nitriding method of metallic aluminum, while in the carbon reduction method of aluminum oxide, a high temperature is required for the reaction, and the raw material price is high. However, there is a problem that aluminum nitride becomes expensive because of its high price.

Therefore, as an improvement of the carbon reduction method for alumina, a method of producing an aluminum nitride powder by firing a precipitate obtained from a suspension containing an aluminum source and carbon powder has been proposed. In this method, aluminum source and carbon powder are only mixed in a suspended state, and mixing on a molecular order is not performed, so that aluminum nitride is produced from the obtained precipitate. Since the reaction requires a high temperature and the firing temperature must be increased, there remains a problem that the manufacturing cost becomes high.

Therefore, the applicant has prepared an aluminum source, a carbon source, and other raw material components as an aqueous solution, removing water from the aqueous solution, and firing the obtained powder in a non-oxidizing atmosphere containing nitrogen to produce aluminum nitride. A method for producing powder has been developed, and a patent application has been filed in Japanese Patent Application No. 61-199742.

According to this manufacturing method, since the respective raw material components are mixed in the aqueous solution in a molecular order, the raw material components are homogeneously mixed in the powder obtained by removing water from the aqueous solution, and The production reaction of aluminum nitride is favorably performed. Therefore, it is possible to obtain fine-grained aluminum nitride powder with extremely high purity, and there is an excellent effect that the manufacturing cost can be reduced because the firing temperature can be relatively low.

[Problems to be Solved by the Invention]

However, as a result of examining the above method in more detail,
It was found that there is still room for improvement in the purity of aluminum nitride obtained by this method.
That is, since the purity of this aluminum nitride affects the quality of the thermal conductivity of the obtained aluminum nitride ceramic substrate, the nitriding ratio is higher, and the carbon residue is further reduced. Therefore, there is a demand for an aluminum nitride ceramic substrate having excellent thermal conductivity.

In view of the above circumstances, it is an object of the present invention to provide a method capable of efficiently and inexpensively producing aluminum nitride powder of even higher purity.

[Means for Solving the Problems]

In order to solve the above problems, the inventor has studied from various directions such as the type of catalyst component that promotes the nitriding reaction, using a water-soluble compound as a raw material component of aluminum nitride,
The present invention has been completed based on the finding that very good results can be obtained by using a water-soluble calcium salt as a catalyst component that accelerates the nitriding reaction during firing.

Therefore, in the present invention, in producing an 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, a water-soluble compound is used as a raw material component of the aluminum nitride. A water-soluble calcium salt is used as a catalyst component that accelerates the nitriding reaction during the calcination, and the calcination is performed on the powder obtained by removing water from an aqueous solution containing these. .

[Action]

If a catalyst component having the action of promoting the nitriding reaction during firing and increasing the reaction rate is added to the raw material component in advance, the nitriding rate is improved and higher purity aluminum nitride can be obtained.

Many of these catalyst components have a function of promoting the decarbonization reaction of aluminum nitride after firing, in addition to the promotion of the nitriding reaction. The acceleration of the decarbonization reaction means that the decarbonization efficiency is increased (the amount of the residual carbon is reduced) when the aluminum nitride powder after firing has residual carbon, or the decarbonization temperature is reduced (about 50 to 100 ° C.). It means to let. Since lowering the decarbonization temperature prevents the oxidation of aluminum nitride during the decarbonization process, the purity of the obtained aluminum nitride is further increased, and finally the aluminum nitride (aluminum nitride ceramics) This leads to the effect of increasing the thermal conductivity.

Calcium salt is a catalyst component that sufficiently exhibits the above two catalytic actions.

Further, by selecting a catalyst component that also has a performance as a sintering aid, a high-purity aluminum nitride powder containing a component that is both a catalyst and a sintering aid can be obtained. This sintering aid promotes the sintering of aluminum nitride, which is difficult to sinter, when firing aluminum nitride powder to produce aluminum nitride ceramics that will serve as an insulating substrate, etc. Is an additive required for obtaining. That is, the sintering aid plays a role of reacting with aluminum nitride to generate a liquid phase, facilitating the sintering of aluminum nitride, and keeping oxygen and the like that hinder the heat dissipation at grain boundaries.

Here, if a water-soluble catalyst component having a performance as a sintering aid is selected and added to an aqueous solution containing a raw material component of aluminum nitride, the raw material component of aluminum nitride and the same catalyst component can be obtained. And will be uniformly dispersed and mixed in the molecular order. Therefore, the mixed powder obtained by removing water from this aqueous solution contains the catalyst components in a homogeneously mixed state, and the aluminum nitride powder obtained by firing the mixed powder also has (catalyst component Especially when a large amount of is used), the sintering aid component is homogeneously contained at the same time as the catalyst component. as a 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 for adding and mixing a sintering aid powder as in the conventional case. Can be eliminated.

That is, conventionally, when manufacturing aluminum nitride ceramics from aluminum nitride powder, Y ₂ O ₃ , CaO or the like in a solid powder state is used as a sintering aid, and these are stirred and mixed with the aluminum nitride powder, followed by an appropriate process. However, there is a problem that it is difficult to uniformly mix the sintering aid powder and the aluminum nitride powder by stirring and mixing them. If the sintering aid and aluminum nitride are not mixed homogeneously, the sintering aid does not work effectively, the aluminum nitride cannot be sintered sufficiently, and the quality performance of the manufactured aluminum nitride ceramics deteriorates. Therefore, this mixing work is very troublesome, and a mixing device for that purpose is also required, which has been a cause of increasing the manufacturing cost of the aluminum nitride ceramics.

However, the presence of excessive catalyst residues in the obtained aluminum nitride powder may adversely affect the electrical characteristics of the aluminum nitride ceramics used as the circuit board, the wiring pattern (electric circuit) adhesion, and the like. However, when the catalyst component is a calcium salt, it works well as a catalyst,
By reducing the addition amount, it is possible to reduce the remaining amount of the catalyst component which becomes an impurity after firing. The addition amount may be increased a little when the calcium salt also serves as the sintering aid, but the addition amount is larger than when the salt is also used as the sintering aid, such as yttrium salt or lanthanide group element. The amount is small and the remaining amount of the catalyst component can be suppressed.

〔Example〕

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

First, as a raw material component of aluminum nitride, a water-soluble aluminum-containing compound and a water-soluble calcium salt as a catalyst component that promotes a nitriding reaction during firing are indispensable, and if necessary, a carbon-containing compound and / or A nitrogen-containing compound or the like is used. That is, when the carbon element or the nitrogen element is contained in the aluminum-containing compound,
It is not necessary to use the carbon-containing compound and the nitrogen-containing compound together.

The aluminum-containing compound serves as a supply source of aluminum which is a main component of aluminum nitride. Therefore, it is not particularly limited as long as it is a compound containing aluminum, but examples thereof include aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum lactate, aluminum polynuclear complex, and aluminum alkoxide. Examples of the polynuclear aluminum 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, aluminum ethoxide, aluminum propoxide, aluminum isopropoxide, and aluminum butoxide are preferably used, but other alkoxides can also be used. These aluminum-containing compounds may be used alone or in combination of two or more.

The carbon-containing compound has a function of removing the oxygen element contained in the mixed powder of the aluminum-containing compound and the like in the form of CO and CO _{2 in} the reaction for producing aluminum nitride in the firing step. Therefore, it is particularly important when the aluminum-containing compound contains a large amount of oxygen element. The carbon-containing compound may be a compound containing a large amount of carbon element, and specifically, sugars such as glucose (glucose), cellulose derivatives of methylcellulose sugar, lignin, polyethylene oxide, polyvinyl alcohol, water-soluble acrylic compounds, Carbon black and the like can be preferably used. These may be used alone or in combination of two or more.

The nitrogen-containing compound has a function of forming a nitrogen source in the mixed powder in the firing step, thereby locally forming a reducing atmosphere with nitrogen inside the mixed powder, and promoting the nitriding of aluminum from the inside of the mixed powder. Fulfill Since the firing atmosphere also contains nitrogen, aluminum nitride can be produced without a nitrogen-containing compound. The nitrogen-containing compound is not particularly limited as long as it contains nitrogen, and examples thereof include water-soluble amino acids such as urea, melamine, and glycine, carbonylhydrazide, ethylenediamine, and the like. In addition to the above, a plurality of kinds may be used in combination.

The water-soluble calcium salt which is a catalyst component has a nitriding promoting action on the aluminum-containing compound at the time of firing, and further has a promoting action on the decarbonization reaction of aluminum nitride after the firing, calcium nitrate, calcium lactate, acetic acid. Examples include calcium and calcium chloride. These catalyst components may be used alone or in combination of two or more.

Some of the catalyst components in the present invention also have a performance as a sintering aid. Therefore, if such a catalyst component is used, an aluminum nitride powder containing a sintering additive component can be obtained. However, in that case, as described below, a larger amount is added than when it is used as a catalyst. That is, when used as a catalyst, it is sufficient to add a so-called catalytic amount, but in order to leave the sintering aid component in the aluminum nitride powder by using it as a sintering aid simultaneously with the catalyst, it evaporates and disappears during firing. It is necessary to set a large amount including the minutes.

The above-mentioned addition amount of the catalyst component is expected only for its effect as a catalyst, or it also has the performance as a sintering aid, and the component is positively left after firing. It depends on whether or not,
It may be appropriately set depending on the use scene so that the best effect is obtained. Specifically, the lower limit is the amount of catalyst, and the upper limit is the amount when left as a sintering aid.
Based on the aluminum nitride powder to be synthesized, it is preferably about 0.3 to 7.0% by weight in terms of each oxide before firing. In the case of calcium salt, the range of 0.3 to 4.0% by weight is more preferable in terms of CaO based on the synthesized A1N powder, and this range is smaller than that in the case of yttrium salt or lanthanide group element salt. . Note that these addition amounts are amounts to be blended with the raw materials, and since some of the catalyst components evaporate during firing, the amount that remains with the aluminum nitride after the actual firing is less than the above addition amount. Become.

In the present invention, the water-soluble raw material component and the water-soluble catalyst component described above are mixed as an aqueous solution, and then the mixed powder obtained by removing the water content is fired. In this way, when mixed in an aqueous solution, each component is homogeneously mixed in the molecular order,
As a result, a mixed powder in which the respective components are homogeneously mixed is obtained, so that the catalytic effect is further enhanced and the nitriding reaction and the like are effectively worked. As the water removing means, a usual water removing means used in the conventional ceramic material manufacturing method can be appropriately adopted.

In particular, the preparation of this aqueous solution is important when the catalyst component is a water-soluble compound that also has the above-mentioned performance as a sintering aid, which allows the sintering aid component to be mixed homogeneously and to have sinterability. It is possible to obtain a good aluminum nitride powder of
It can be a more preferable raw material for producing aluminum nitride ceramics.

The firing conditions are not particularly limited, but for example, the temperature is 900 ° C. or higher, preferably 1200 to
A range of 1800 ° C is chosen. As the non-oxidizing atmosphere, a gas containing nitrogen such as ammonia, a mixed gas of nitrogen and hydrogen, or the like can be used in addition to argon, carbon monoxide, and nitrogen gas. In this firing step, nitrogen and aluminum are combined to produce aluminum nitride, and oxygen elements, which are impurities, are burned and removed.

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

The manufacturing method of the present invention is not limited to the above-described example, and in addition to the above-described steps, other steps used in a normal ceramic powder manufacturing method can be appropriately added if necessary.

Hereinafter, more detailed examples of the present invention will be described together with comparative examples. First, we will describe each example when paying attention to the catalyst performance, but all the catalyst components used also have the performance as a sintering aid, and the sintering aid can be adjusted by adjusting the addition amount. An easily sinterable aluminum nitride powder is obtained which can be sintered without the addition of an agent.
-Example 1-A1 to be synthesized with calcium nitrate as a catalyst component in an aqueous solution prepared by mixing aluminum sulfate with methylcellulose so as to have a C / A1 (element blending molar ratio) of 3.0
The N powder was mixed so as to be 0.5 wt% in terms of CaO. Water was evaporated from the obtained aqueous solution to obtain a mixed powder, which was then baked in a nitrogen stream at 1600 ° C. for 5 hours to obtain an aluminum nitride powder. Further, the obtained aluminum nitride powder was subjected to a heat treatment in air at 600 ° C. for 6 hours to remove unreacted residual carbon.

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

-Example 2-In a solution prepared by dispersing aluminum propoxide in isopropyl alcohol, C / A1 is 0.5 and 0.5% by weight in terms of CaO based on A1N powder synthesized.
A mixed aqueous solution of glucose and calcium nitrate was added so that The amount of glucose added was calculated excluding the amount of carbon contained in aluminum propoxide. Water was removed from this mixed solution to obtain a mixed powder, which was then fired in the same manner as in Example 1 to obtain an aluminum nitride powder, and an aluminum nitride sintered body was manufactured.

-Examples 3 to 5 Using the raw material components and catalyst components shown in Table 1, an aqueous solution was prepared, water was removed, and the mixture was baked in the same manner as in Example 1 above to obtain an aluminum nitride powder. Furthermore, when the produced aluminum nitride powder contained the catalyst component in an amount that can also be expected to function as a sintering aid, an aluminum nitride sintered body was produced in the same manner as in Example 1 above. In Example 4, the glucose addition amount was calculated in consideration of the amount of carbon contained in the basic aluminum lactate.

-Comparative Example- An aluminum nitride powder was produced in the same manner as in Example 1 except that the catalyst component was not added and the raw material components shown in Table 1 were used.

With respect to the obtained aluminum nitride powders of Examples and Comparative Examples, the nitriding rate and the residual carbon amount were obtained, and the density and the thermal conductivity of the sintered body were measured.

The above results are also shown in Table 1.

As can be seen from Table 1, in the examples, as compared with the comparative examples, high-purity aluminum nitride powder having a high nitriding rate and a small carbon residual amount was obtained, and the addition amount of the catalyst component was a so-called catalyst amount. It was confirmed that the effect was sufficiently exhibited even with a small amount. When the aluminum nitride powder contains a sufficient amount of catalyst component, that is, a sintering aid,
An aluminum nitride sintered body having a very high thermal conductivity was produced from the powder.

Next, as Examples 6 and 7, specific examples will be shown in which the catalyst component is positively expected to have a performance as a sintering aid. In each of the examples, the raw materials shown in Table 2 were used to prepare an aqueous solution, and the firing conditions were a firing temperature of 1600 ° C. and a firing time of 6 hours in a nitrogen atmosphere.

Similarly, Table 2 shows the nitriding ratio and particle size of the manufactured aluminum nitride powder.

As shown in Table 2, aluminum nitride fine particles having a high nitriding rate can be obtained also from these examples, and the aluminum nitride powder is subjected to the mixing step of the sintering aid as in the conventional case. Instead, it can be used as it is for the sintering production of aluminum nitride ceramics.

〔The invention's effect〕

According to the method for producing an aluminum nitride powder according to the present invention described above, the nitriding reaction is promoted by the action of an appropriate catalyst component of calcium salt, and depending on the type of the catalyst component (in many cases), after calcination Since decarbonization is also facilitated, high-purity aluminum nitride powder can be manufactured at low temperatures.

Furthermore, by using a water-soluble compound that also has a performance as a sintering aid as a catalyst component, and mixing with a raw material component of aluminum nitride in an aqueous solution state, both are homogeneous in molecular order. By mixing, finally, a high-purity aluminum nitride powder in which the sintering additive components are homogeneously mixed can be obtained. Therefore, unlike the conventional method for manufacturing aluminum nitride ceramics, the step of stirring and mixing the fired aluminum nitride powder and the sintering aid in the form of a solid powder is not required. Moreover, as a result of the homogenous dispersion and mixing in the molecular order, the aluminum nitride ceramics is satisfactorily sintered, and a ceramic product excellent in quality performance can be manufactured.

In addition, the catalyst made of calcium salt is inexpensive and easily available, which is convenient in terms of production, and as a result, inexpensive aluminum nitride powder can be easily obtained. In the case of yttrium salt and lanthanide group elements, the price is higher than that of calcium salt.
It is disadvantageous in terms of availability.

In addition, the aluminum nitride powder obtained does not leave an excessive catalyst residue.

This is because a small amount of calcium salt has a sufficient effect and the amount of addition of the calcium salt can be reduced to reduce the residual amount of the catalyst which becomes an impurity after firing. For example, when an aluminum nitride ceramics sintered body for a circuit board is manufactured using aluminum nitride powder, if the residual amount of the catalyst is too large, the electrical characteristics will deteriorate. With this, it is possible to reduce the amount of addition of the catalyst and suppress the amount of the catalyst residue that becomes an impurity after firing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Bando 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-62-265106 (JP, A) JP-A-52-297205 ( JP, A)

Claims (1)

[Claims] 1. A method for producing an 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, wherein a water-soluble compound is used as the raw material component of aluminum nitride. A water-soluble calcium salt is used as a catalyst component for accelerating the nitriding reaction during the calcination, and the calcination is performed on the powder obtained by removing water from an aqueous solution containing these. How to make powder.