JPS6110071A - High heat conductivity aluminum nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a highly thermally conductive aluminum nitride sintered body.

[Technical background of the invention and its problems]

Aluminum nitride (AJQJ) has high strength from room temperature to high temperature (the bending strength of the sintered body is usually 50 to 2/1112
Since it has excellent chemical resistance, it is used as a heat-resistant material, and its high thermal conductivity and high electrical insulation properties make it a promising material for heat sinks in semiconductor devices. Such AIN usually has no melting point, 2200℃
Because it decomposes at higher temperatures, it is used as a sintered body except for applications such as thin films.

Incidentally, AIN sintered bodies have conventionally been manufactured by the pressureless sintering method and the hot pressing method. In the hot press method,
Sintering is carried out under high temperature and high pressure using AIN alone or AA'N to which an auxiliary agent has been added. However, with the hot press method, it is difficult to manufacture a sintered body with a complicated shape, and furthermore, the productivity is low and the cost is high.

On the other hand, in the pressureless sintering method, silicon oxide or the like is added as a sintering aid for the purpose of increasing density.

Although this pressureless sintering method can solve the problems of the hot press method, the thermal conductivity of the obtained AIN sintered body is A
While the theoretical thermal conductivity of IN is 320 W/m-, it is as low as 40 W/m·K. In addition, among the A/N sintered bodies made by the hot press method, AJ to which an auxiliary agent was added
Those made from N also have a thermal conductivity of 40 W/rn・K
The degree is low.

[Purpose of the invention]

The present invention aims to provide a highly thermally conductive aluminum nitride sintered body with improved thermal conductivity compared to conventional ones.

[Summary of the invention]

The present inventors have discovered that A
As a result of various studies regarding the low thermal conductivity of the AIN sintered body, it was determined that this low thermal conductivity is due to the amount of auxiliary agent in the AIN sintered body as well as the oxygen content, which is involved in sinterability. A.I.N.
It is necessary for the raw material to contain oxygen in order to improve sinterability and obtain a dense AA'N sintered body, but when the amount of oxygen increases, it becomes a factor that inhibits high thermal conductivity. I found out that it will happen.

Therefore, the present inventors conducted further intensive research based on the above investigation results, and found that aluminum nitride containing 0.001 to 7% by weight of oxygen contains 1 selected from alkaline earth metals and their compounds that will eventually become oxides. By mixing 0.002 to 15% by weight of alkaline earth metals and sintering, a highly thermally conductive aluminum nitride sintered body with extremely high thermal conductivity compared to conventional aluminum nitride sintered bodies can be produced. I found it. It is presumed that the reason why the aluminum nitride sintered body of the present invention exhibits high thermal conductivity is due to the structure described below.

Added alkaline earth metals or compounds containing them,
When the oxygen-containing AJN raw material is shaped and sintered, the alkaline earth metal reacts with the oxygen in the AIN (usually present as aluminum oxide) to form the composition formula 6 Al2O,-MeO
,2Al2O3-Meo, 3Al2O,-5Me
OXAA! 205 ・Some of the alkaline earth metal/aluminum composite oxides expressed in the form of MeO (where Me is an alkaline earth metal) are produced, and this compound promotes sintering and ultimately forms AIN. The alkaline earth metals gather at the grain boundaries and fix the oxygen in AlN.
Which aluminum composite oxide is produced depends on the amount of oxygen in aluminum nitride, the amount of alkaline earth metal added, and the firing conditions.

However, when the amount of oxygen in the AJN raw material increases, there will be oxygen that cannot be incorporated into the alkaline earth metal/aluminum composite oxide, and that oxygen
Solid solution diffusion into N particles.

The thermal conductivity of an insulator is controlled by the diffusion of elastic waves (phonons), but A
In the IN sintered body, phonons are scattered in the solid solution diffused region, resulting in a decrease in thermal conductivity. However, AI
In consideration of the amount of alkaline earth metal added, the amount of nitrogen raw material oxygen is suppressed and fixed to the amount that constitutes the alkaline earth metal/aluminum composite oxide, and by preventing solid solution diffusion into AIN, phonon Less scattering results in improved thermal conductivity.

That is, the present invention uses aluminum nitride containing 0.001 to 7% by weight of oxygen, and one or more selected from alkaline earth metals and their compounds, which will eventually become oxides, in an amount of 0.002 to 7% by weight in terms of alkaline earth metals. 15% by weight and sintered.

The reason for limiting the amount of oxygen in the AIN is that the amount is o,
If it is less than o o i weight%, a tough A with high sinterability can be obtained.
However, if the amount of the lN sintered body exceeds 7% by weight, the generated compound tends to wrap around the grains, resulting in a decrease in thermal conductivity. In addition, when using the pressureless sintering method as the sintering method, the above-mentioned oxygen content is 0.05 to 5% by weight.
, more preferably 0.05 to 1% by weight, and when using the hot press method, 0.001 to 3% by weight, and even more preferably 0.001 to 1% by weight.

The alkaline earth metals include Mg, Ca1Sr,
Examples of the alkaline earth metal compounds include oxides, carbonates, oxalates, sulfates, and nitrates. These alkaline earth metals may be used alone or in a mixture of two or more. The reason for limiting the content ratio of alkaline earth metals, etc. to the above range is that if the amount is less than 0.002% by weight, a dense AJN sintered body with high sinterability cannot be obtained; When the amount exceeds 15% by weight, the absolute amount of AlN decreases, and the heat resistance and high strength, which are the inherent characteristics of the AlN sintered body, are impaired, and the thermal conductivity also decreases. In addition,
When containing these alkaline earth metals and their compounds, etc., it is desirable to increase the content within the above range (0,002 to 15% by weight) when the oxygen content in the AIN raw material is high. Further, when pressureless sintering is employed, it is desirable that the proportion of alkaline earth metals etc. be 0.1 to 15% by weight.

Next, one manufacturing method for obtaining the AIIN sintered body of the present invention will be explained.

First, alkaline earth metals and their compounds are added to AIN powder containing a predetermined amount of oxygen, and after mixing using a ball mill etc., in the case of pressureless sintering, a binder is added, cross-wiring, granulation, and sizing are performed. Then, molding is performed using a mold, isostatic press, or sheet molding. Subsequently, the molded body is heated at around 700° C. in a N2 gas stream to remove the binder. Next, the molded body was set in a graphite or aluminum nitride container, and heated at 1600 to 1900 in a N2 gas atmosphere.
Pressureless sintering is performed at ℃. At this time, relatively low temperature (1000
The above-mentioned alkaline earth metal/aluminum composite oxide is produced at a temperature of 1,300° C. to 1,300° C., melts at an even higher temperature, and undergoes pressureless sintering by its liquid phase sintering mechanism.

On the other hand, in the case of hot press sintering, the raw materials mixed in the ball mill or the like are boiled at 1600 to 1900°C.

[Embodiments of the invention]

Next, the present invention will be explained in detail.

Example 1 First, aluminum nitride powder containing 3% by weight of oxygen (
A raw material was prepared by adding 3% by weight of strontium powder powder (average particle size: 1 μm) to the powder (average particle size: 1 μm), and grinding and mixing using a ball mill. Next, this raw material was filled into a carbon mold with a diameter of 10 m, and a pressure of 300ψ-
A MN sintered body was produced by hot pressing at a temperature of 1800° C. for 1 hour.

Comparative Example 1 Example 1 except that aluminum nitride powder (average particle size 1 μm) itself containing 3% by weight of oxygen was used as the raw material.
A fi AIN sintered body was manufactured in the same manner as above.

Comparative Example 2 3% by weight of strontium powder (average particle size: 1 μm) was added to aluminum nitride powder (average particle size: 0.9 μm) containing 10% by weight of oxygen, and the raw materials were ground and mixed using a ball mill. Prepared. Next, using this raw material, hot pressing was performed in the same manner as in Example 1 to obtain AI! A N sintered body was manufactured.

Therefore, the A obtained by the above Example 1 and Comparative Example 1.2
After polishing each JN sintered body to a thickness of 3.5 mm, the thermal conductivity at room temperature was measured by a laser flash method.

As a result, in the AJN sintered body of Example 1, 58 W/i
n-, whereas the AJIN sintered body of Comparative Example 1 had a power of 36 W/im・K, and the AIN sintered body of Comparative Example 2 had a power of 36 W/im・K.
It was 2 W/rn・K.

In addition, when the constituent phases of each AA'N sintered body were investigated by X-ray diffraction, it was found that the A/N phase and the
03-8rO% 2k120. -8rO phase is Comparative Example 1
In addition to the AJi'N phase, there was a large amount of oxynitride phase, and in Comparative Example 2, there was an AlN phase and Al2O5.Sr0, 2A1
20. In addition to the -8rO phase, an amount of oxynitride phase of Kana 9 was detected.

Example 2 Raw materials were prepared in the same manner as in Example 1, except that calcium carbonate powder was used in place of the strontium powder, and the raw materials were hot pressed to produce an AIN sintered body.

After polishing the obtained AIN sintered body to a thickness of approximately 3.5 m, the thermal conductivity at room temperature was measured using the laser flash method, and it showed an extremely high thermal conductivity of 75 W/in・K. . In addition, when the structure of the A/N sintered body was examined by X-ray diffraction, it was found that the structure was A7N phase, Az2o, ・cao, 2AJ
A zOs·CaO phase was detected.

Examples 3 to 8 Calcium carbonate powder (average particle size 1 μm) was added to aluminum nitride powder (average particle size 09 μm) containing 3% by weight of oxygen.
0.1% by weight, 0.5% by weight, 1% by weight, 2% by weight,
After adding 3% by weight and 5% by weight, they were milled using a mail mill for 10 hours and mixed to prepare 5 types of raw materials each weighing 2,009 yen. Next, 7% by weight of Noya rough-in was added to each of these raw materials, and after granulation, 300 kg 7 cm2
It was cold-formed at a pressure of 37 m x 37 m x 6 crn to form a plate-shaped body. Next, these plate-shaped bodies were heated to 200°C in a nitrogen gas atmosphere, held for 10 hours to degrease them, and then placed in an aluminum nitride container and sintered at 1800°C under nitrogen gas atmosphere for 2 hours under normal pressure. Six types of AlN sintered bodies were manufactured.

Each AI obtained! The density and thermal conductivity of the N sintered body were investigated. The results are shown in Table 1 below.

In Table 1, an AlN sintered body produced in the same manner as in Example 3 is also listed as Comparative Example 3, except that aluminum nitride powder without calcium carbonate was used as the raw material.

Table 1 Also, the structures of the AlN sintered bodies of Examples 3 to 7 were examined by X-ray diffraction. As a result, Izushi 4 A#J phase, 6k1203-CaO% 2AA! 20. -ChO%
3A1203 '5CaO1A120. - A CaO phase and a slight oxynitride phase were detected, but as the amount of CaCO3 added increased, the oxynitride phase decreased and the alkaline earth metal/aluminum composite oxide phase increased. Moreover,
Among the composite oxide phases, as the amount of Ca C03 added increases, the proportion of the oxide phase with a high CaO/All 205 ratio increases.

Examples 9 to 12 MgCO3 and CaCO with an average particle size of 1 μm were added to aluminum nitride powder (average particle size 1 μm) containing 1% by weight of oxygen.
5,5rCO5 and BaCO5 were added in an amount of 3% by weight, wet-pulverized using a mail mill, and mixed to prepare four types of raw materials. Subsequently, pressureless sintering was performed in the same manner as in Example 3 using these raw materials.

The thermal conductivity of each of the obtained AA'N sintered bodies of Examples 9 to 12 was examined. The results are shown in Table 2 below. In addition, Table 2 also shows as a reference example an AA'N sintered body hot-pressed at the same temperature using aluminum nitride powder as a raw material with no additives added.

Table 2 Also, each of the A7N sintered bodies of Examples 9 to 12 was 3.211
It had a density of 7 cm3 or more.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a highly thermally conductive aluminum nitride sintered body which has extremely high thermal conductivity compared to conventional ones and is effective for heat sinks of semiconductor devices and the like.

Claims (1)

[Claims] aluminum nitride containing 0.001 to 7% by weight of oxygen;
One or more selected from alkaline earth metals and their compounds that will eventually become oxides with an alkaline earth metal equivalent of 0.0
A highly thermally conductive aluminum nitride sintered body obtained by mixing and sintering 02 to 15% by weight of aluminum nitride.