JP2525166B2 - Aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nitride having high thermal conductivity, which is produced from an aluminum nitride sintered body, particularly an aluminum nitride raw material powder obtained by direct nitriding of metallic aluminum. The present invention relates to an aluminum sintered body.

(Problems to be Solved by Conventional Techniques and Inventions) In recent years, with the development of LSIs, insulation with high thermal conductivity for mounting semiconductor elements with high heat generation such as highly integrated circuits, power transistors, laser diodes, etc. Materials are needed.

As such a ceramic material having high thermal conductivity,
Beryllium oxide (BeO) -based sintered bodies have been used in the past, but their range of use is limited due to their toxicity.

Therefore, aluminum nitride (A1N), which has high thermal conductivity, stability, high temperature strength, and good electric insulation, has been used as a highly heat conductive substrate material that can replace beryllium oxide.

Aluminum nitride has characteristics suitable for semiconductor substrates as described above, and although the theoretical value of its thermal conductivity is very high at about 300 W / m · k, at present, the thermal conductivity is generally about 100 W.
An aluminum nitride sintered body having a low value of / m · k or less has not been obtained, and improvement of the thermal conductivity of the aluminum nitride sintered body is desired.

Since aluminum nitride powder is difficult to sinter and is difficult to sinter by itself, a sintering aid is added to the aluminum nitride raw material powder to produce a sintered body. As the auxiliary agent, a group IIa metal (alkaline earth metal) or a group IIIa metal (Y and rare earth metal) of the periodic table is used.
Have been proposed, such as Y ₂ O ₃ , CaO, and CaC ₂ . (See JP-A-59-207814, JP-A-60-60910, JP-A-60-71575) As a typical method for producing aluminum nitride powder,
(1) Method of directly nitriding metallic aluminum powder with nitrogen or ammonia gas (direct nitriding method), and (2) Mixing alumina powder with carbon powder and firing in nitrogen or ammonia gas to reduce alumina by carbon. The method of doing (carbon reduction method) is known. Among them, in the direct nitriding method, in the step of pulverizing metallic aluminum as a raw material in order to increase the nitriding efficiency, or in the step of finely pulverizing the produced aluminum nitride powder to a particle size suitable for the firing raw material, a pulverizing container or pulverizing medium Usually, several percent by weight of cation impurities are inevitably mixed, and further, the powder surface is oxidized in the above fine pulverization step, and the oxygen content in the aluminum nitride raw material powder by the direct nitriding method is 2% by weight or more, Reaches over 3% by weight. The aluminum nitride powder containing a large amount of oxygen and cation impurities is not suitable as a raw material for obtaining a high-quality aluminum nitride sintered body, and in fact, it has been conventionally burned from the raw material powder obtained by the direct nitriding method. It has not been generally performed to produce a sintered body having a high thermal conductivity using a binder.

On the other hand, in the carbon reduction method, since alumina is pulverized to a desired particle size in advance and carbon reduction and nitriding are performed, the content of cationic impurities in the produced aluminum nitride powder is as low as 0.5% by weight or less, and the content of oxygen is reduced. Usually about 3
%, Which is relatively small, and a high-purity fine powder having an average particle diameter of 2 μm or less can be easily obtained. Since this fine powder can be used as a raw material for sintering without further crushing treatment, in the production of an aluminum nitride sintered body, the fine powder of aluminum nitride obtained by the carbon reduction method is used for firing. The method of sintering with a co-agent is widespread.

However, even with such fine powder, the thermal conductivity of the obtained aluminum nitride sintered body is still 100 W / m · k or less, which is significantly lower than the theoretical value of about 300 W / m · k. It was

The yttrium compound is used as a sintering aid at 100 W / m.
A method for producing an aluminum nitride sintered body having a high thermal conductivity of k or more is disclosed in JP-A-60-178688 and 61-
Although disclosed in Japanese Patent No. 91068, it is not suggested to use the raw material powder obtained by the direct nitriding method in any of the methods, and the method described in JP-A No. 61-91068 discloses sintering. In order to reduce the oxygen content of the body and improve the thermal conductivity, free carbon or a carbonaceous substance is present in addition to the aluminum nitride raw material powder and the sintering aid at the time of sintering to achieve deoxidation, A troublesome manufacturing method is used.

Comparing the aluminum nitriding process of direct nitriding method and carbon reduction method, the manufacturing process of direct nitriding method is simple, only the step of heating metal aluminum powder in nitrogen or ammonia gas, while carbon reduction method Requires multiple steps of (1) mixing alumina powder and carbon powder, (2) heating the mixed powder in nitrogen or ammonia gas, and (3) removing residual unreacted carbon by oxidation. .
As a result, the manufacturing cost of the aluminum nitride powder produced by the direct nitriding method is 1/4 to 1/6 that of the carbon reduction method.
Very low with the degree.

Therefore, if an aluminum nitride sintered body having high thermal conductivity and high strength can be manufactured by using the aluminum nitride raw material powder obtained by the direct nitriding method, it will contribute greatly to the cost reduction of the aluminum nitride sintered body. Become.
However, as described above, since the fine aluminum nitride raw material powder produced by the direct nitriding method has poor purity,
It has been the actual situation that it has not been conventionally used for producing a high thermal conductivity sintered body. Note that FIG. 2 shows an electron micrograph of the aluminum nitride powder obtained by the carbon reduction method, and FIG. 3 shows an electron micrograph of the aluminum nitride powder obtained by the direct nitriding method.

(Means for Solving the Problems) An object of the present invention is to provide an aluminum nitride sintered material having high thermal conductivity and high strength, which is manufactured at low cost from an aluminum nitride raw material powder obtained by a direct nitriding method. It is to be.

The inventors of the present invention, when the aluminum nitride raw material obtained by the direct nitriding method is used to achieve high thermal conductivity and high strength, Y ₂ O ₃ added as a sintering aid in the aluminum nitride sintered body is used.
By controlling the oxygen content remaining after subtracting the oxygen content in the Y ₂ O ₃ content from the content of and the total oxygen content in the sintered body within a specific range, at the same time high thermal conductivity is achieved, It was found that high thermal conductivity and high strength can be achieved at the same time by controlling the remaining oxygen amount so that the Al ₂ O ₃ conversion amount and the Y ₂ O ₃ amount have a specific relationship.

That is, the present invention is the following aluminum nitride sintered body.

(1) Aluminum nitride-based firing obtained by molding and firing a mixed powder in which a sintering aid made of Y ₂ O ₃ or a precursor thereof is added to an aluminum nitride raw material powder obtained by direct nitriding of metallic aluminum in body, the sintered body, the conversion of Y content of the sintered body in terms Y ₂ O ₃ content was calculated as Y ₂ O ₃ with respect to (wt%), the total oxygen content of the sintered body Y ₂
The point plotting the remaining oxygen amount (% by weight) after subtracting the oxygen amount in the O ₃ content is the line segment I-J-K-N in FIG.
Within the range surrounded by -I, and the remaining oxygen content
Convert content of Al ₂ O ₃ in terms as _{Al 2 O 3 (Al 2 O} 3 wt%)
Conversion to Y ₂ O ₃ content (Y ₂ O ₃ wt%) Weight ratio (Al ₂ O 3
₃ / Y ₂ O ₃ ), and converted Al ₂ O ₃ and converted Y ₂ O ₃ contents have the following relations 0.6 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≦ 1.4 (weight ratio), 3.2 ≦ Al ₂ O ₃ Satisfies ≤7.0 (wt%), 3.9 ≤ Y ₂ O ₃ ≤7.0 (wt%), has a thermal conductivity of 140 W / m · k or more, and has a three-point bending resistance strength of 40 kg / mm ² or more, relative An aluminum nitride sintered body having a density of 95% or more.

(2) In the aluminum nitride sintered body according to the item (1), the Y ₂ O ₃ content converted from the total oxygen content of the sintered body with respect to the Y content (% by weight) of the sintered body The point that plotted the remaining oxygen amount (wt%) after subtracting the oxygen amount in the
It is within the range surrounded by the line segment O-P-L-M-O in FIG. 1, and the converted Al ₂ O ₃ amount and the converted Y ₂ O ₃ amount are 0.6 ≦ Al ₂ O ₃ / Y ₂ O. Satisfies the relationship of ₃ ≤ 1.2 (weight ratio), 3.2 ≤ Al ₂ O ₃ (weight ratio%) ≤ 6.0, 4.5 ≤ Y ₂ O ₃ (weight%) ≤ 6.0, and with a thermal conductivity of 160 W / m ・ k or more. An aluminum nitride sintered body characterized by being present.

 Hereinafter, the present invention will be described in more detail.

The aluminum nitride sintered body according to the present invention, as described above, is produced from the aluminum nitride raw material powder obtained by the direct nitriding method using Y ₂ O ₃ or its precursor as a sintering aid. And is composed of an AlN phase and a Y-containing grain boundary phase, and has a thermal conductivity of at least 100 W / m · k,
Preferably 120 W / m · k or more, more preferably 140 W / m ·
k or more, most preferably 160 W / m · k or more, and the relative density is 95% or more, more preferably 97% or more, particularly preferably 98.5% or more.

When using the yttrium compound, Y ₂ O ₃ from about 2 to 12 wt% amounts are converted of the entire sintered body as, preferably from about 3.9 to 9.0 wt%, more preferably from about 3.9 to 7.0 wt%,
Particularly preferably, it is in the range of about 4.5 to 6.0% by weight.

The phase structure of the aluminum nitride sintered body produced by using the sintering aid is composed of AlN particles and the grain boundary phase connecting these particle phases.

The composition of the crystal phase existing in the grain boundary phase varies depending not only on the type of the sintering aid, but also on the purity of the raw material powder and the manufacturing conditions such as the firing temperature and the atmosphere. The thermal conductivity greatly depends on the composition of this grain boundary phase. When Y ₂ O ₃ is added as a sintering aid, the grain boundary generation phase is YAG (Y ₃ Al ₅ O ₁₂ ), YAlO ₃ , Y ₄ Al ₂ O ₉ , Y ₂ O ₃ , AlN
・ Al ₂ O ₃ spinel, YN, unknown phase, and 27R-polytype (a kind of SIALON).

As a result of experiments, the present inventor has found that among these grain boundary formation phases, one or both of YAlO ₃ and Y ₄ Al ₂ O ₉ , especially Y ₄ Al ₂ O ₉
It was found that the thermal conductivity of the aluminum nitride-based sintered body becomes very high when is present as the main phase in the grain boundary. The reason is not fully understood, but probably
The predominant presence of YAlO ₃ and / or Y ₄ Al ₂ O ₉ enhances the smoothness or consistency of the edges between the aluminum nitride particles, as well as the thermal conductivity of these grain boundary forming phases themselves. It is thought that the high thermal conductivity can be obtained because the heat diffusion through the grain boundaries is promoted because of the good heat resistance. If many other crystal phases are generated at the grain boundaries, it is difficult to obtain smoothness or consistency of the sides between the aluminum nitride particles.
(Y ₃ Al ₅ O ₁₂ ) has a low thermal conductivity of about 12 W / m · k, and Y ₂ O ₃ has a low thermal conductivity of about 27 W / m · k, which deteriorates the thermal diffusivity at grain boundaries. .

The above preferred grain boundary forming phase YAlO ₃ and Y ₄ Al ₂ O ₉ are
AlN and Y ₂ O ₃ sintering aids during firing, its precursors or, although the oxygen inevitably present as impurities in the aluminum nitride raw material powder is one which produced by the reaction,
In order that the grain boundary generation phase is mainly composed of such a crystal phase, the ratio of Y atoms and Al atoms in the grain boundary phase of the sintered body may be within a certain range.

In most cases, yttrium is present as an oxide in the sintered body, so the measured yttrium amount can be converted to Y ₂ O ₃ amount by multiplying it by 1.27 times.

In addition, it is considered that in the aluminum nitride sintered body, most of all oxygen in the sintered body exists as oxides at the grain boundaries, and the other oxygen is solid-dissolved in the AlN lattice. A part of oxygen existing in the grain boundary is made of Y ₂ O _{3 which} is a sintering aid or a precursor thereof.
The rest is oxygen existing in the aluminum nitride raw material powder or bound to the cation impurities mixed in in the manufacturing process. In the present invention, the total oxygen content and the Y content in the sintered body are measured, the measured Y content is converted to Y ₂ O ₃ , and an amount is calculated. From the total oxygen content, the Y content is calculated as Y ₂ O _3. The remaining oxygen amount is obtained by subtracting the oxygen amount in the amount converted as. That is, the remaining oxygen amount = total oxygen amount− (converted Y ₂ O ₃
Amount) x 0.212.

The present inventor prepared a number of aluminum nitride sintered body samples by using aluminum nitride raw material powder obtained by the direct nitriding method, and set the Y content of the sintered body to Y ₂ O as described above. _The value converted as ₃ (referred to as the converted Y ₂ O ₃ content) and the remaining amount (referred to as the remaining oxygen content) obtained by subtracting the oxygen content in this converted Y ₂ O ₃ content from the total oxygen content of the sintered body As a result of investigation of the tendency of thermal conductivity as a relation, it was found that these values must be within a certain range in order to obtain a sintered body having high thermal conductivity.

That is, FIG. 1 is a composition diagram in which the horizontal axis represents the converted Y ₂ O ₃ content (wt%) of the aluminum nitride sintered body and the vertical axis represents the remaining oxygen amount (wt%). , Thermal conductivity is 10
For the aluminum nitride sintered body of 0 W / m · k or more, the remaining oxygen amount is plotted against the converted Y ₂ O ₃ amount of the sintered body,
It is obtained when it is within the range surrounded by the line segment QRS-TQ shown by the broken line in this figure (however, not included on the line).

A sintered body showing a thermal conductivity of 120 W / m · k or more has a line segment A-
It can be obtained when it is within the range surrounded by B-C-D-E-F-G-H-A (including the line, but not including the point C).

The plot of the aluminum nitride sintered body showing a thermal conductivity of 140 W / m · k or more according to the present invention has a line segment I-J-K-N-I.
It can be obtained when it is within the range surrounded by (including on the line). Furthermore, in the most preferred embodiment of the present invention, the plot is within the range surrounded by the line segment O-P-L-M-O (including the line), and in this case, the sintered body is 160 W / m.・ It shows very high thermal conductivity of k or more. In addition, in FIG. 1, the line segment shown by the solid line means that the line is included, and the broken line means that the line is not included.

In FIG. 1, the horizontal axis of points A to T (converted Y ₂ O ₃ content,
The values of (% by weight) and the vertical axis (remaining oxygen content,% by weight) are as follows.

In another preferred embodiment of the present invention, there is provided an aluminum nitride sintered body which exhibits high thermal conductivity and high bending strength. The sintered body with high bending strength was obtained by converting the remaining oxygen amount (that is, the oxygen amount obtained by subtracting the oxygen amount in the converted Y ₂ O ₃ amount from the total oxygen amount) into Al ₂ O ₃ (% by weight). ) (Hereinafter referred to as the converted Al ₂ O ₃ amount) and the converted Y ₂ O ₃ amount, and the ratios thereof, were found to be obtainable. That is, the above converted Al ₂ O
₃ amount and converted Y ₂ O ₃ amount (all are weight%), 0.2 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≦ 2.4 (weight ratio), 1.1 ≦ Al ₂ O ₃ ≦ 12.0, 2.0 <Y ₂ O ₃ If the relationship of <12.0 is satisfied, it is possible to obtain an aluminum nitride sintered body having a thermal conductivity of 100 W / m · k or more and a bending strength (3-point bending test, the same applies below) of 30 kg / mm ² or more. .

The above converted Al ₂ O ₃ amount and converted Y ₂ O ₃ amount are 0.2 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≦ 1.7 (weight ratio) 1.1 ≦ Al ₂ O ₃ ≦ 11.0 3.9 ≦ .Y ₂ O ₃ ≦ 9.0 If the relationship of
It can show a thermal conductivity of 120 W / m · k or more and a bending strength of 35 kg / mm ² or more. Furthermore, in the sintered body of the present invention, the converted Y ₂ O ₃ amount of the converted Al ₂ O ₃ amount is 0.6 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≦ 1.4 (weight ratio), 3.2 ≦ Al ₂ O ₃ ≦ The relationship of 7.0, 3.9 ≦ Y ₂ O ₃ ≦ 7.0 is satisfied, and in this case, the sintered body exhibits a thermal conductivity of 140 W / m · k or more and a bending strength of 40 kg / mm ² or more.

In particular, the above converted Al ₂ O ₃ content and converted Y ₂ O ₃ content are 0.6 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≦ 1.2 (weight ratio), 3.2 ≦ Al ₂ O ₃ ≦ 6.0, 4.5 ≦ Y ₂ O _When the relationship of ₃ ≤ 6.0 is satisfied, the thermal conductivity of the sintered body is 160 W / m ・
The bending strength is 40 kg / mm ² or more, which is a very high value.

The grain boundary phase is mainly composed of a crystal phase formed by Y and Al being heated at a high temperature during firing as described above. However, the grain boundary phase is an unavoidable cation impurity that may be present in the aluminum nitride sintered body, and then a large amount. It is generally silicon (Si) that is present. Silicon is inevitably mixed in, but if the ratio of Si to Y is too high in the aluminum nitride sintered body,
Even if the amount of oxygen is kept low, it is difficult to improve the thermal conductivity. As will be described later, Si causes a solid solution in AlN particles or reacts with AlN to cause deterioration of the thermal conductivity of the sintered body. However, the Y component present as a sintering aid is a solid solution of Si or AlN. It is thought to suppress the reaction of. However, if the ratio of Si to Y is too large, this effect of Y is not sufficiently exerted,
Therefore, it is considered that the thermal conductivity cannot be improved. In a preferred embodiment of the aluminum nitride sintered body of the present invention,
Content of Y atoms and Si atoms contained in the sintered body (% by weight)
However, if Si / Y ≦ 1.32 (weight ratio), Si ≦ 1.3, 1.6 <Y <9.4 (the last formula is expressed as Y ₂ O ₃ , 2.0 <Y ₂ O ₃ <12.0), then The sintered body can exhibit a thermal conductivity of 100 W / m · k or more.

Further, the content (% by weight) of Y atoms and Si atoms is Si / Y ≦ 0.21 (weight ratio), Si ≦ 0.9, 3.1 ≦ Y ≦ 7.1 (the last formula is expressed as Y ₂ O ₃ , 3.9 ≦ Y ₂ O ₃ ≦ 9.0) is satisfied, the sintered body becomes 12
It exhibits a thermal conductivity of 0 W / m · k or more.

Furthermore, more preferably, the content (% by weight) of Y atoms and Si atoms is Si / Y ≦ 0.12 (weight ratio), Si ≦ 0.5, 3.1 ≦ Y ≦ 5.5 (when the last formula is expressed as Y ₂ O ₃ , 3.9 ≦ Y ₂ O ₃ ≦ 7.0)
The sintered body of the present invention has a thermal conductivity of 0 W / m · k or more.

And most preferably, the content (% by weight) of Y atom and Si atom is Si / Y ≦ 0.05 (weight ratio), Si ≦ 0.2, 3.5 ≦ Y ≦ 4.7 (corresponding to 4.5 ≦ Y ₂ O ₃ ≦ 0.6) When the above condition is satisfied, the sintered body can exhibit a very high thermal conductivity of 160 W / m · k or more.

When the composition of the grain boundary phase was examined as the composition ratio of the metal element component, it was found that the aluminum nitride sintered body having high thermal conductivity had the composition ratio of the metal element component within the specific range. That is, in a preferred embodiment of the aluminum nitride sintered body of the present invention, the metal element component present in the grain boundary phase is based on the total weight of the metal elements, Y: 60 to 91% by weight, Al: 8 to 35% by weight. %, Si: 10% by weight or less. Such a sintered body can exhibit a high thermal conductivity of 140 W / m · k or more. Further, the ratio of this metal element component is Y: 70 to 91.
A sintered body composed of wt%, Al: 8 to 25 wt%, Si: 3 wt% or less is particularly preferable, and such a sintered body can exhibit a very high thermal conductivity of 160 W / m · k or more. If Y does not reach 60% by weight, the bending strength tends to decrease in addition to the decrease in thermal conductivity. If the Al content is less than 8% by weight, the bending strength of the sintered body decreases, and if it exceeds 35% by weight, both the thermal conductivity and the bending strength decrease, and ALON (AlN ・ Al ₂ O ₃ spinel) is generated.

On the other hand, when Si exceeds 10% by weight, the thermal conductivity is remarkably lowered, and in this case, SIALON and unknown crystallites are formed in the grain boundary phase.

The relative density with respect to the theoretical density of the aluminum nitride sintered body of the present invention is at least 95%, preferably at least 97%, particularly preferably at least 98.5%.

The aluminum nitride sintered body of the present invention is manufactured from the raw material powder obtained by the direct nitriding method. The aluminum nitride raw material powder used has an oxygen content of less than 1.8% by weight,
The average particle size is 1 to 3 μm, the Si content is 0.2 or less, and the purity is 99% or more. Here, the "oxygen content" of the aluminum nitride raw material powder is the total amount of oxygen atoms contained in the raw material powder as a compound such as an oxide or as oxygen.

The "purity" of the raw material powder is defined as the total amount (% by weight) of cationic impurities, which is the remainder obtained by subtracting Al, N, O, and adsorbed moisture from the aluminum nitride raw material powder.
It is a value obtained by subtracting this total amount of cationic impurities from 0%. That is, a purity of 99% or more means that the total amount of such cationic impurities is 1% by weight or less. Such impurities include Fe, C, Si, Ti,
V, Cr, Mn, Ca, Mg, Co, Ni, etc. may be mentioned. These cationic impurities are measured by ICP (plasma emission spectrometry) and atomic absorption spectrometry. Preferably, the content (% by weight) of each such impurity is within the following range.

Fe: 0.001 to 0.08%, C: 0.01 to 0.07%, Si: 0.2% or less, Ti, V, Ci, Mn, Ca, Mg: 0.01% or less each, Co, Ni: 0.001% or less each.

The purity of the raw material powder used in the production of the aluminum nitride sintered body of the present invention is preferably 99.5% or more, more preferably 99.7% or more. If the purity of the raw material powder is less than 99%, the main impurity in the raw material powder is Si, and if it is large, the thermal conductivity deteriorates.

Among the above-mentioned cation impurities, Si dissolves in AlN or reacts with AlN during firing, resulting in AlN polytype (SIAL
ON, Al-Si-O-N). This Al
Since N polytype promotes grain growth during firing, it is known that a fibrous composition is easily formed and thermal conductivity is deteriorated.Therefore, the content of Si in the raw material powder is set as described above.
Setting it to 0.2% or less is important for further improving the thermal conductivity of the aluminum nitride sintered body of the present invention.

When the oxygen content of the raw material powder is 1.8% by weight or more, the oxygen content of the sintered body generally mixed with Y ₂ O ₃ and fired is too high, and the sintered body showing a high thermal conductivity as intended. It becomes difficult to obtain a union. Therefore, such high-purity aluminum nitride raw material powder is produced by the direct nitriding method of heating high-purity metallic aluminum (preferably 98.5% or more in purity) powder in ammonia or nitrogen. Then, the obtained aluminum nitride powder is finely pulverized to a desired particle size in a non-oxidizing atmosphere (eg, nitrogen, argon, helium, carbon monoxide, hydrogen gas atmosphere) or in an organic solvent. Commercially available aluminum nitride powder produced by direct nitriding of high-purity metallic aluminum is also available.

The fine pulverization of the fine powder of aluminum nitride powder is preferably performed in an organic solvent because the cationic impurities tend to be less mixed. The organic solvent that can be used may be any one regardless of polarity or nonpolarity, and examples thereof include alcohols, ketones, aldehydes, aromatic hydrocarbons,
Paraffin hydrocarbons can be used. The pulverization step can be performed after mixing with the sintering aid, that is, for the mixed powder.

The average particle size of the raw material powder is suitably 1 to 3 μm or less. If the average particle size is larger than this, the thermal conductivity, the relative density, and the bending strength of the obtained sintered body decrease.

The aluminum nitride sintered body of the present invention is produced by mixing an appropriate amount of a sintering aid with the above-mentioned raw material powder, and molding and firing this mixed powder by a conventional method.

More preferred is a sintering aid consisting only of Y ₂ O ₃ or its precursor, or a mixture consisting mainly of Y ₂ O ₃ or its precursor and other sintering aids, but in some cases other firings. A co-agent and the like may be further added. Precursor of Y ₂ O ₃ is not particularly limited as long as it is thermally decomposed into Y ₂ O ₃ in the firing temperature, yttrium carbonate To exemplify [Y ₂ CO _3], yttrium acetate _{[Y (CH 3 CO 2)} 3] , yttrium nitrate _{[Y (NO 3) 3]} , oxalic yttrium _{[Y (C 2 O 4)} 3]
And so on.

When the sintering aid consists of Y ₂ O ₃ or its precursor,
The compounding amount to be added is selected so that the converted Y ₂ O ₃ amount in the sintered body falls within the predetermined range shown in FIG. That is, since it is considered that Y atoms do not substantially escape from the compact during the composition, the weight ratio of Y ₂ O ₃ to the weight of the mixed powder of the aluminum nitride raw material powder and the firing aid is within the range specified in FIG. It should be. Specifically, the converted Y ₂ O ₃ based on the mixed powder is 3.9 to 7.0% by weight (point K to point N in FIG. 1).
Point), most preferably 4.5 to 6.0% by weight (point L to point M), and the Y ₂ O ₃ or its precursor is adjusted and used.

Further, in consideration of the oxygen contents of the aluminum nitride raw material powder and the sintering aid, the above-mentioned "remaining oxygen content" in the sintered body should be within the range specified in FIG. Select the type and blending amount of. Since firing is performed in a non-oxidizing atmosphere (including in vacuum) as described below, the oxygen content in the mixed powder of the aluminum nitride raw material powder and the firing aid is
It can be considered to be substantially the same as the oxygen content in the sintered body with almost no increase. Therefore, make sure that the remaining oxygen content, which is obtained by subtracting the oxygen content in the Y ₂ O ₃ content (or its precursor) from the total oxygen content in the mixed powder, falls within the range specified in Fig. 1. Good. Specifically, the range of the remaining oxygen content varies depending on the compounding amount of Y ₂ O ₃ , but is 0.38 to 6.69 wt% (S point to Q in FIG. 1).
Points), preferably 0.38 to 4.92% by weight (points C to A), more preferably 1.28 to 3.67% by weight (points K to I), most preferably 1.41 to 3.15% by weight (points L to O). is there.

The above range of the remaining oxygen content is converted into the amount of Al ₂ O ₃ assuming that the remaining impurities are all Al ₂ O ₃ (that is, expressed as the converted Al ₂ O ₃ content). , 2.72 ~ 7.80
%, Most preferably 3.00 to 6.69% by weight.

In order to secure a high bending strength of the sintered body, as described above, the ratio of the converted Al ₂ O ₃ content / converted Y ₂ O ₃ content, and Al ₂ O ₃ and Y ₂ O _{3 are used.} Since it is preferable that the respective converted contents of the above are within a certain range, in that case, in the mixed powder of the raw material powder and the sintering aid, the converted Al ₂ O ₃ content /
The raw material powder purity and the blending amount of the sintering aid are selected so that the ratio of the converted Y ₂ O ₃ contents and the respective converted contents of Al ₂ O ₃ and Y ₂ O ₃ are within a predetermined range.

Further, as described above, the amount of Si in the mixed powder also greatly affects the thermal conductivity of the sintered body, so the Si atom in the mixed powder is
It is preferable that the weight ratio of / Y atoms and the content of each of these atoms fall within the ranges described above for the sintered body.

As the sintering aid, it is preferable to use one having an average particle size of about 0.5 to 3 μm.

The aluminum nitride raw material powder and the sintering aid are mixed by dry mixing in a non-oxidizing atmosphere or by wet mixing using an organic solvent. Wet mixing using organic solvents such as aromatic hydrocarbons, ketones and alcohols is preferable. If the average particle size of the mixed powder is too large,
As mentioned above, it is also possible to simultaneously pulverize the mixed powder during this mixing. For the firing of the mixed powder, a small amount of an appropriate binder (for example, one or more kinds of paraffin wax, stearic acid, polyvinyl butyral, ethyl cellulose, a copolymer of methyl methacrylate and ethyl acrylate, etc.) is added to the mixed powder. By a suitable molding means such as a dry pressing method, a rubber pressing method, an extrusion method, an injection method, a doctor blade sheet molding method, a casting molding method, etc. It can be carried out by firing at a high temperature in a non-oxidizing atmosphere under pressure or pressure (for example, an inert atmosphere such as nitrogen, argon, helium gas, or an inert atmosphere further containing hydrogen). Or
Molding and firing can be performed simultaneously by the hot pressing method.

The firing temperature varies depending on the firing method, but is generally 1500-
It is preferably in the range of 2100 ° C, and if it is lower than 1500 ° C, sufficient densification cannot be achieved, and if it exceeds 2100 ° C, sublimation decomposition of aluminum nitride is likely to occur. When the normal pressure firing is adopted, the firing temperature is preferably 1750 to 1950 ° C, more preferably 1860 ° C or less, and most preferably 1840 ° C.

Firing by hot pressing is preferably performed at 1600 to 1800 ° C. When the firing is performed under pressure (that is, a gas pressure of 1 atm or less), the firing temperature is preferably in the range of 1880 to 1970 ° C. Firing of the hot isostatic press (HIP) is preferably performed at a temperature within the range of 1500 to 2000 ° C.

(Example) Example 1: As a raw material powder for manufacturing a sintered body, various aluminum nitride raw material powders were prepared with an aluminum nitride powder obtained by direct nitriding of metallic aluminum. Oxygen content of the obtained aluminum nitride raw material powder, Si content,
The purity and average particle size are shown in Table 1 below.

To these aluminum nitride raw material powders, Y ₂ O ₃ powder (average particle size 1.3 μm) was added as a sintering aid in a ratio shown in Table 2 (A-1) and (A-2) below. Al ₂ O ₃ powder (average particle size 1.5 μm) or Si ₃ N ₄ (average particle size
0.9 μm) was added, and this mixture was mixed and finely ground by wet ball milling in methanol or toluene to obtain a mixed powder.

The compositions of the aluminum nitride raw material powder and the additive components are shown in Table 2 (A-1) and (A-2).

6% by weight of paraffin wax and 13% of stearic acid as a binder to the mixed powder of each sample of No. 1 to 13, 8 "and 14 to 50
The mixture added with wt% was pressed at a molding pressure of 1000 kg / cm ² to form a green compact having a diameter of 12 mm. This green compact was fired in a nitrogen atmosphere at a temperature of 1600 to 1800 ° C. for 0.5 hour to obtain a sample of an aluminum nitride fired body.

Although there are powders obtained by adding Al ₂ O ₃ or Si ₃ N ₄ powder to the above-mentioned mixed powder, the reason is that these are the components that are mixed as impurities from the raw material powder or in the manufacturing process such as the pulverization process. , Was intentionally added to evaluate the effect of the presence of these impurities on the thermal conductivity.

For the sample thus obtained, thermal conductivity (measurement by laser flash method: error due to thickness of measured sample was corrected), relative density (Archimedes method), and bending strength (3-point bending bending test, JIS R1601) Was measured, and the test results showing Tables (B-1) and (B-2) were obtained.

Table 2 (A-1) and (A-2) also show the average particle diameter of the aluminum nitride raw material powder in the mixed powder and the additive mixed powder used for the preparation of the powder mixture, the firing temperature of the compact, Then, in Tables 2 (B-1) and (B-2), the Y element content in the obtained sintered body and the converted Y ₂ O ₃ content obtained by converting this into Y ₂ O ₃ are shown. the remaining oxygen content obtained by subtracting the oxygen content of Y ₂ O ₃ content converted from the total oxygen content, and in terms content of Al ₂ O ₃ This was calculated as Al ₂ O _3, Si element content of the sintered body Amount (below, all weight%),
The weight ratio of converted Al ₂ O ₃ / converted Y ₂ O ₃ and the element weight ratio of Si / Y are also shown.

The oxygen content of the aluminum nitride raw material powder and the sintered sample was measured by infrared absorption analysis (LECO TC-136), and the Si content was measured by ICP (emission spectroscopy, Seiko Denshi Kogyo). did. As a result of measuring the Y ₂ O ₃ content of the raw material mixed powder, the remaining oxygen content, the Al ₂ O ₃ conversion content, the Si element content, etc., it was found to be almost the same as the composition in the sintered body.

FIG. 4 is a plot of the converted Y ₂ O ₃ amount and the remaining oxygen amount in each of the sintered body samples in Tables (B-1) and (B-2) in the same composition diagram as FIG. 1. The value in parentheses next to the sample No. is the thermal conductivity of the sintered sample (unit: W / m
k). It can be seen from Fig. 4 that the thermal conductivity does not reach 100 W / m ・ k on the line of the quadrilateral formed by the line segment QRS-T-Q, but inside the quadrilateral 100 W / m ・ k In addition, the thermal conductivity of the sintered body is 120 W within the range surrounded by the line segment A-B-C-D-D-E-F-G-A (including the line segment).
/ m · k or more, which is the sintered body of the present invention, the line segment I-J
Within the range surrounded by -K-N-I (including the line), the thermal conductivity is 140 W / mk or more, and the line segment O-P-L-M-O
It can be seen that a very high thermal conductivity of 160 W / m · k or more can be obtained within the range surrounded by (including the line).

In FIG. 4, sample Nos. 7, 12, and 13 are not plotted because the remaining oxygen amount is unknown. Sample Nos. 8 to 11 and 30 to 34 are omitted because they are plotted at points very close to other samples, but these are all omitted by the line segment O-P-L-M.
It is in the range surrounded by -O and exhibits a thermal conductivity of 160 W / m · k or more.

Moreover, from the results of Table 2 (B-1) and (B-2), the ratio of converted Al ₂ O ₃ / converted Y ₂ O ₃ and each converted Al ₂ O ₃ and Y ₂ O _{3 are shown.}
It is also understood that when the amount is within a certain range as described above, not only the thermal conductivity but also the bending strength can be improved.

Furthermore, comparing sample Nos. 1 and 2 in Table 2 (B-1) and (B-2) with sample Nos. 8 to 11, the Y content was the same, and the remaining oxygen content was the same as sample No. 1.93 for .1 and 2
˜2.30% by weight, and in Sample Nos. 8-11, it is approximately equal to or less than 1.95-1.09% by weight, but the sintered bodies of Samples No. 8-11 have high Si content and therefore have high thermal conductivity. It can be seen that it will decrease. From sample Nos. 30 to 34, the thermal conductivity is affected not only by the oxygen content but also by the Si content, and it is effective to improve not only the oxygen content but also the Si content to improve the thermal conductivity. I know there is.

In addition, from the results of Table 2 (B-1) and (B-2), Si
It can also be seen that an improvement in thermal conductivity can be obtained when the element weight ratio of / Y and the weight% of each of these elements are within a certain range as described above.

As shown in Table 1, sample Nos. 49 and 50 have an oxygen content of more than 1.8% in the raw material powder, but these show that the thermal conductivity of the sintered body is 100 W / mk or less. There is.

Example 2: For the sample Nos. 1 to 34 obtained in Example 1, the grain boundary crystal phase generated at the grain boundaries was confirmed by the powder X-ray diffraction method. The results are shown in Table 3 below. The numerical values in Table 3 were examined by the ratio of the crystal phase having the highest peak height of X-ray intensity as 100% and the other crystal phases.

Judging from the results of Table 2 (B-1), (B-2) and Table 3, those containing Al ₂ Y ₄ O ₉ as the main phase were 167 W except for those with a large Si content in sample No. 10. / m ・ k or more, those with AlYO ₃ as the main phase are about 138 W / m ・ k or more, and those with Al ₅ Y ₃ O ₁₂ as the main phase are all except sample No. 7 which has a large oxygen content. It can be seen that it has a thermal conductivity of 102 W / m · k or more.

Although the above-mentioned sintered body was subjected to the atmospheric pressure method, the test results with the same tendency were obtained by the hot pressing method, and the density of the sintered body was further increased, so that the thermal conductivity was also increased.

(Effects of the Invention) As described above, where a high thermal conductivity aluminum nitride-based sintered body could not be obtained even by using conventional high-purity aluminum nitride powder raw materials and various sintering aids, in the present invention, It is possible to provide an aluminum nitride-based sintered body that has much higher thermal conductivity and higher mechanical strength than conventional products.

[Brief description of drawings]

FIG. 1 is a composition diagram showing a suitable range of the converted Y ₂ O ₃ amount and the remaining oxygen amount in the aluminum nitride sintered body of the present invention.
The figure is an electron micrograph of the aluminum nitride raw material powder obtained by the carbon reduction method of alumina, FIG. 3 is the electron micrograph of the aluminum nitride raw material powder obtained by the direct nitriding method of metallic aluminum, and FIG. FIG. 3 is a drawing in which the converted Y ₂ O ₃ amount and the remaining oxygen amount of the aluminum nitride-based sintered body samples obtained in Examples are plotted on the composition diagram of FIG. 1.

Claims (2)

(57) [Claims] 1. An aluminum nitride obtained by molding and firing a mixed powder in which a sintering aid made of Y ₂ O ₃ or its precursor is added to an aluminum nitride raw material powder obtained by direct nitriding of metallic aluminum. in quality sintered body, the sintered body is converted Y ₂ O ₃ content was calculated as the Y content of the sintered body Y ₂ O ₃ with respect to (wt%), from said total oxygen content of the sintered body The point plotting the remaining oxygen amount (wt%) after subtracting the oxygen amount in the converted Y ₂ O ₃ content is the line segment I-J- in FIG.
Converted Y ₂ O ₃ content of converted Al ₂ O ₃ content (Al ₂ O ₃ wt%) within the range surrounded by KNI and converting the remaining oxygen content as Al ₂ O ₃ . The weight ratio (Al ₂ O ₃ / Y ₂ O ₃ ) to (Y ₂ O ₃ wt%), and the converted Al ₂ O ₃ and converted Y ₂ O ₃ contents are in the following relationship 0.6 ≦ Al ₂ O ₃ / Y ₂ O ₃ ≤ 1.4 (weight ratio), 3.2 ≤ Al ₂ O ₃ ≤ 7.0 (wt%), 3.9 ≤ Y ₂ O ₃ ≤ 7.0 (wt%), and a thermal conductivity of 140 W / m ・ k or more. However, an aluminum nitride sintered body having a three-point bending resistance of 40 kg / mm ² or more and a relative density of 95% or more. 2. The residual oxygen content (weight) obtained by subtracting the oxygen content in the converted Y ₂ O ₃ content from the total oxygen content of the sintered body with respect to the Y content (weight%) of the sintered body. %) Is plotted within the range surrounded by the line segment O-P-L-M-O in FIG. 1, and the converted Al ₂ O ₃ amount and the converted Y ₂ O ₃ amount are 0.6%. Satisfies the relationship of ≤ Al ₂ O ₃ / Y ₂ O ₃ ≤ 1.2 (weight ratio), 3.2 ≤ Al ₂ O ₃ (weight%) ≤ 6.0, 4.5 ≤ Y ₂ O ₃ (weight%) ≤ 6.0, and conducts heat The aluminum nitride sintered body according to claim 1, characterized in that the rate is 160 W / m · k or more.