JPH07121829B2 - High thermal conductivity aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a dense and uniform high thermal conductivity aluminum nitride sintered body.

(Prior Art) Aluminum nitride (AlN) is used as a heat-resistant material because it has little strength deterioration even at high temperatures and is excellent in chemical resistance. It is also promising as a heat sink material and an insulating material for circuit boards. Such aluminum nitride does not have a melting point under normal pressure and decomposes at a high temperature of 2500 ° C. or higher, so it is used as a sintered body except for applications such as thin films.

Such an aluminum nitride sintered body is usually obtained by molding and sintering aluminum nitride powder. When using ultra-fine powder (about 0.3 μm or less) of AlN powder, a dense sintered body can be obtained by itself, but the oxygen in the oxide layer on the surface of the raw material powder becomes a solid solution in the AlN lattice during sintering. , Al-O-N compound is produced, and as a result, the thermal conductivity of the added sintered body is at most 100 w / m.
It is about K. Further, when AlN powder having a particle size of 0.5 μm or more is used, the sinterability is not good, so that it is difficult to obtain a dense sintered body without addition except by the hot pressing method. Therefore, when trying to obtain a sintered body at atmospheric pressure, rare earth oxides are used as sintering aids in order to increase the density of the sintered body and prevent solid solution of impurity oxygen in the AlN raw material powder into AlN grains. It is generally practiced to add an alkaline earth metal oxide or the like (JP-A-60-127267, JP-A-61-1007).
No. 1, JP-A-60-71575, etc.). These sintering aids are AlN
It reacts with the impurity oxygen of the raw material powder to generate a liquid phase and achieves the densification of the sintered body, and at the same time, the impurity oxygen is fixed as a grain boundary phase (oxygen trap) to achieve high thermal conductivity.

By adding the sintering aid in this way, the sintered body surely becomes densified and has high thermal conductivity, but on the other hand, as a result, a considerably large amount of grain boundary phase remains, so that the sintered body is It has a non-uniform microstructure, resulting in problems such as non-uniform mechanical properties and non-uniform color tone. Also, this grain boundary phase (which is the main phase
Due to the existence of (sub-phase to AlN phase) and oxygen that could not be completely trapped, that of the aluminum nitride sintered body was lower than the theoretical thermal conductivity of AlN of 320 w / mK.

Therefore, various attempts have been made for the purpose of obtaining a dense and uniform high-thermal-conductivity aluminum nitride sintered body, but none of them has been sufficiently satisfied.

(Problems to be Solved by the Invention) At present, there is a demand for a material having a higher thermal conductivity for a circuit board for mounting a semiconductor, a heat dissipation board and the like. However, oxygen and other impurities, especially non-uniformity of the sintered body due to the existence of the grain boundary phase formed at the grain boundary as a result of the addition of the auxiliary agent, and the high thermal conductivity of the obtained aluminum nitride sintered body There was a limit.

The present invention has been made in consideration of the above points, and an object thereof is to provide an aluminum nitride sintered body having excellent thermal conductivity.

[Structure of Invention]

(Means and Actions for Solving Problems) The inventors of the present invention have determined the sintering aid, the sintering conditions, the composition of the sintered body, the microstructure of the sintered body, etc., to be added to the aluminum nitride powder in order to achieve the above object. As a result of conducting experiments and studies on the relationship of thermal conductivity, the inventors have invented the following new matters and completed the present invention.

That is, when a yttrium compound was added to AlN powder as a sintering aid, embedded in carbon and fired, YC ₂ was used in place of the conventionally known Y—Al—O-based compound grain boundary phase.
It was found that a small amount of Y-C-based compound such as, etc. was formed, and the sintered body (in some cases, Y ₂ O ₃ was formed) was uniform and had improved thermal conductivity. This effect was similarly observed with other rare earth elements.

Based on this fact, the present invention is the result of various examinations on the optimum conditions for achieving the uniformity of the AlN sintered body and achieving high thermal conductivity.
C-based compound phase (or added to this (rare earth element) -O
A high thermal conductivity aluminum nitride sintered body characterized by containing a system compound phase), a rare earth element content of 4000 ppm or less, and an impurity oxygen content of 3000 ppm or less.

This sintered body can be manufactured as follows.

a) The amount of impurities oxygen is 7% by weight or less and the average particle size is 0.
A molded product obtained by mixing aluminum nitride powder having a particle size of 05 to 5 μm with 0.01 to 15% by weight of the rare earth element in terms of weight of rare earth element, or molding, or having a rare earth element content of 0.01 to 15% by weight and oxygen content. A sintered body having a content of 0.01 to 20% by weight and having AlN as a main phase and containing a (rare earth element) -Al-O compound phase and / or a (rare earth element) -O compound is embedded in b) carbon. C) Baking for 4 to 720 hours at 1550 to 2050 ° C. in a non-oxidizing gas atmosphere.

It can be manufactured by the method.

The aluminum nitride sintered body obtained by such a method was a dense and uniform polycrystalline body and had a thermal conductivity of 180 w / mK or higher, which was higher than that of the conventional one. When observing the constituent phases of this sintered body using X-ray diffraction and an electron microscope, clean AlN crystal grains are in surface contact with each other, and three or more grains are in contact with each other and a very small number of rare earth elements (rare earth elements). ) -C compound is very uniformly present. In addition, when a component analysis was performed, it was a novel aluminum nitride sintered body containing Al and N as main components, containing a rare earth element of 4000 ppm or less, impurity oxygen of 3000 ppm or less, and other impurity cation elements of 1000 ppm or less. From the viewpoint of improving thermal conductivity, rare earth elements are 150 to 4
It is preferable that the concentration of 000 ppm and the oxygen content of impurities are 1500 ppm or less. In the sintered body of the present invention, it is desirable that the amount of impurity oxygen is as small as possible, and the impurity cations resulting from the raw material powder also cause a decrease in thermal conductivity, so it is desirable that the amount is as small as possible.
Good characteristics were obtained when the (rare earth element) -C compound phase was essential as the sub-phase.

Next, a method for producing the high thermal conductivity aluminum nitride sintered body of the present invention will be described.

The production method of the present invention is based on the purity and average particle size of the aluminum nitride raw material powder, the sintering aid, the sintering container, the sintering time and the firing atmosphere.

As the aluminum nitride raw material powder as the main component, oxygen is 7 wt% or less in consideration of sinterability and thermal conductivity, and practically
The content of 0.01 to 7% by weight and the average particle size of 0.05 to 5 μm are used.

A rare earth element compound (especially yttrium compound is preferable) is used as an additive. As the compound of the rare earth element, an oxide, a nitride, a fluoride, an oxyfluoride, an oxynitride, or a substance which becomes these compounds by firing is most suitable. Examples of the substance that becomes an oxide by firing include carbonates, nitrates, oxalates, and hydroxides of these elements.

Addition of rare earth element compound is 0 in terms of weight of rare earth element.
Add in the range of 01 to 15% by weight. If the added amount is less than 0.01% by weight, the effect of the additive is not sufficiently exerted,
The sintered body is not densified, or oxygen does not form a solid solution in the AlN crystal to obtain a high thermal conductive sintered body. Also, if the addition amount is too large, the grain boundary phase remains in the sintered body, or the volume of the grain boundary phase removed by the heat treatment is large, so pores remain in the sintered body and shrinkage occurs. The rate becomes very large, and there are disadvantages such as the shape being broken. It is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight.

In the method of the present invention, a molded body in which such an AlN powder and a rare earth element compound are mixed may be fired under the conditions described below, and a rare earth element may be prepared by a conventional method (for example, JP-A-61-117160). Content is 0.01-15% by weight, oxygen content is 0.
01 to 20% by weight, with AlN as the main phase (rare earth element) -A
A sintered body composed of the l-O compound phase and / or the (rare earth element) -O compound phase may be produced and used in place of the above-mentioned compact.

Regarding the baking container, aluminum nitride, alumina, Mo, etc. are sufficient for the purpose of simply densifying the molded body (JP-A-61-146769, etc.). However, with these containers, a large amount of (rare earth elements)
The -Al-O compound phase and the like remain inhomogeneously present in the sintered body, and an AlN sintered body with high thermal conductivity cannot be obtained. In the present invention, it is embedded in carbon and fired. As such a method, it is possible to bury the entire container in carbon powder, carbon fiber, or carbon fiber. This carbon has an effect of reducing aluminum nitride during firing. More specifically, the grain boundary phase such as (rare earth element) -Al-O ternary compound is removed from the sintered body, and the balance Acts as a (rare earth element) -C compound at the ridges or triple points of the AlN grains, and the aluminum nitride sintered body changes to a uniform and highly heat-conductive sintered body.

Regarding the sintering time, a large amount of (rare earth element) -Al-O-based compound phase is present even if fired in the above-mentioned carbon in a short time which is generally less than 4 hours, and a uniform and high thermal conductivity is obtained. AlN sintered body cannot be obtained. Further, when the firing container that does not provide the carbon atmosphere as described above is used, the effect of the present invention cannot be obtained regardless of the firing time. Although it depends on the sintering temperature and the amount of auxiliary agent added, the present invention requires firing for 4 to 720 hours.

The firing temperature is preferably 1550 to 2050 ° C. 1550 ° C
If fired at a lower temperature, a dense sintered body cannot be obtained. Also
When fired at a temperature higher than 2050 ° C, the vapor pressure of AlN itself increases and it becomes difficult to densify it. More preferably the firing temperature
It is 1700-2000 ℃. Furthermore, 1750-1950 degreeC is preferable.

The firing atmosphere is preferably one or more non-oxidizing atmospheres selected from the group consisting of vacuum, hydrogen gas, carbon monoxide, argon and the like. When firing in an oxidizing atmosphere, not only the effect of purifying the grain boundaries of carbon does not work, but also high thermal conductivity cannot be obtained due to solid solution of oxygen and generation of different phases. The firing is performed under atmospheric pressure including vacuum, reduced pressure, increased pressure and normal pressure.

Next, an example of the method for producing the aluminum nitride sintered body of the present invention will be described below.

First, a predetermined amount of a rare earth element compound as a sintering additive is added to AlN powder and then mixed using a ball mill or the like. An atmospheric pressure sintering method is used for sintering. In this case, a binder is added to the mixed powder, kneading, granulating and sizing are performed, and then molding is performed. As a forming method, a die press, a hydrostatic press, a sheet forming or the like can be applied. Subsequently, the molded body is heated in a non-oxidizing atmosphere, for example, in a nitrogen gas stream to remove the binder, and then sintered under normal pressure. At this time, it is embedded in carbon and fired.

The sintering temperature is set to 1550 to 2050 ° C and the sintering time is set to 4 to 720 hours. The sintered body of the present invention can be obtained by such a method.

Next, the effect of improving the uniformity or thermal conductivity of the aluminum nitride sintered body of the present invention and the formation of the (rare earth element) -C compound and the (rare earth element) -O compound will be described. The exact mechanism has not been completely clarified at present, but according to the study by the present inventors, it is presumed as a factor of the homogenization and the high thermal conductivity as follows.

First is the effect of trapping impurity oxygen in the AlN raw material powder by adding a rare earth element. That is, by adding a rare earth element compound as a sintering aid, the impurity oxygen is fixed to the edges and triple points of the AlN grain boundary in the form of (rare earth element) -Al-O compound, etc. The solid solution of oxygen is prevented, and the formation of Al oxynitride (AlON) and AlN polytype (27R type) is prevented. According to the results of research conducted by the inventors, it is known that the sintered bodies produced by AlON and 27R type have low thermal conductivity. Suppressing such a cause of the low thermal conductivity is one of the causes of the high thermal conductivity.

If you choose Y as the rare earth element impurities oxygen raw material _{powders, 3Y 2 O 3 · 5Al 2} O 3, Y 2 O 3 · Al 2 O3,2Y 2 O 3 · Al 2 O 3, Y 2
It is trapped as a compound such as O ₃ . This state occurs at the initial stage of sintering, that is, usually within 0 to 1 hour of the sintering time.

In the subsequent sintering process, carbon reduces the grain boundary phase and further begins to remove the grain boundary phase. Gradually, the grain boundary phase does not exist in the aluminum nitride sintered body and moves out of the system of the sintered body. And finally, the sintered body contains a trace amount (rare earth element)
The -C type compound or the (rare earth element) -O compound phase is uniformly contained, and the thermal conductivity and the uniformity are improved. This is because the grain boundary phase, which has small thermal conductivity and worked as thermal resistance, is removed.

Due to the above reasons, a highly heat conductive aluminum nitride sintered body can be obtained. The most effective rare earth element in the present invention was yttrium. Further, the sub-phase in the present invention is a trace amount, and since the presence of a large amount is accompanied by a decrease in thermal conductivity, the density of the sintered body is 3.255 to 3.285 g / cm.
It is preferably ³ . The particle size of the sintered body is preferably 3 μm or more in consideration of thermal conductivity.

(Example) Example 1 Oxygen as an impurity was contained by 1.0% by weight, and the average particle size was 0.6.
AlN powder of μm, Y ₂ O _{3 with} an average particle size of 0.9 μm as an additive
4% by weight in terms of the weight of yttrium element was added, and the raw materials were adjusted by mixing using a ball mill. Then,
4% by weight of organic binder was added to this raw material and granulated, then press molded at a pressure of 500 Kg / cm ² to produce 38 × 38 × 10 mm
Of green compact. This green compact is 700 times in a nitrogen gas atmosphere.
The binder was removed by heating to ° C. Further, it was embedded in a carbon felt and housed in a carbon container. The shape and size of the container (A) at this time is 10 cmφ x 3.7 c
It has a volume of about 290 cm ³ and is filled with carbon felt. Using this container, atmospheric pressure sintering was carried out in an argon gas atmosphere (1 atm) at 1950 ° C. for 24 hours. Got
The AlN sintered body had a density of 3.269 g / cm ³ and a particle size of 13 μm. A disk having a diameter of 10 mm and a thickness of 3.3 mm was ground from the sintered body, and the thermal conductivity was measured by a laser flash method using this as a test piece. (Use TC-3000 manufactured by Vacuum Riko). The thermal conductivity of the sintered body was 225 w / mK (25 ° C).

Further, this sintered body was analyzed. Yttrium content is determined by ICP emission spectroscopy (Seiko Denshi Kogyo SPS-1200A
It was 1000 ppm due to use). Cationic impurities were less than 200ppm (mainly Fe and Si) by chemical analysis. The oxygen content was measured by fast neutron activation analysis.
(Using Toshiba's NAT-200-1C) The result was 650 ppm. Results of X-ray diffraction of this sintered body (Rigaku Denki rotor flex RU-200, goniometer CN2173D5, radiation source Cu50K
The presence of a YC ₂ compound phase as a sub-phase other than AlN was confirmed.

Example 2 An AlN sintered body was manufactured in the same manner as in Example 1 except that the addition amount of the sintering aid was changed to 7 Wt%. The sintered body was identified to have AlN as the main phase and YC ₂ as the subphase. The Y content in the sintered body is 1
The content was 600 ppm, the oxygen content was 550 ppm, the density was 3.275 g / cm ³ , the average particle amount was 12 μm, and the thermal conductivity was 212 W / mK.

Example 3 An AlN sintered body was manufactured in the same manner as in Example 1 except that the sintering temperature was changed to 1750 ° C. The sintered body has AlN as the main phase and Y as the sub-phase.
C ₂ , Y ₂ O ₃ were identified. The Y content in the sintered body is 2200
ppm, oxygen content was 1200 ppm, density was 3.284 g / cm ³ , average particle size was 10 μm, and thermal conductivity was 195 w / mK.

Example 4 An AlN sintered body was produced in the same manner as in Example 1 except that the sintering temperature was 2000 ° C. and the sintering atmosphere was changed to 10 atm of argon gas.
The sintered body has AlN as the main phase and YC ² is identified as the ^secondary phase, and the Y content in the sintered body is 2400 ppm and the oxygen content is 1400 pp.
m, density 3.274 g / cm ³ , average particle size 18 μm, thermal conductivity 1
It was 98 w / mK.

Example 5 An AlN sintered body was manufactured in the same manner as in Example 1 except that the sintering time was 12 hours and the sintering atmosphere was changed to 0.1 atm of hydrogen. The main body of the sintered body was AlN, and YC ₂ was identified as the subphase. The Y content in the sintered body is 2600 ppm, the oxygen content is 1200 ppm, the density is 3.275 g / cm ³ , the average particle size is 11 μm, and the thermal conductivity is 200 w / m.
It was K.

Example 6 An AlN sintered body was manufactured in the same manner as in Example 1 except that a carbon container filled with carbon powder was used. The main body of the sintered body was AlN, and YC ₂ was identified as the subphase. The Y content in the sintered body is 2100 ppm, the oxygen content is 900 ppm, the density is 3271 g / cm ³ , the average particle size is 12 μm, and the thermal conductivity is 205 w / mK.
Met.

Example 7 Example 1 except that a carbon container was used for the entire inside.
An AlN sintered body was manufactured in the same manner as in. The main body of the sintered body was AlN, and YC ₂ was identified as the subphase. In addition, Y in the sintered body
Content is 1500ppm, oxygen content is 700ppm, density is 3.270
The particle size was g / cm ³ , the average particle size was 13 μm, and the thermal conductivity was 199 w / mK.

Example 8 An AlN sintered body was produced in the same manner as in Example 1 except that CeO ₂ was used instead of Y ₂ O ₃ . The sintered body has AlN as the main phase,
There was a phase presumed to be a CeC ₂ compound as a subphase. Also, the Ce content in the sintered body is 2300 ppm, the oxygen content is 6
The density was 50 ppm, the density was 3.280 g / cm ³ , the average particle size was 10 μm, and the thermal conductivity was 180 w / mK.

Example 9 An AlN sintered body was produced in the same manner as in Example 1 except that La ₂ O ₃ was used instead of Y ₂ O ₃ . The sintered body had AlN as a main phase and a phase presumed to be a LaC ₂ compound as a subphase. The La content in the sintered body was 1600 ppm, the oxygen content was 600 ppm, the density was 3.270 g / cm ³ , the average particle size was 12 μm, and the thermal conductivity was 188 w / mK.

Comparative Example 1 An AlN degreased body obtained in the same manner as in Example 1 was manufactured in the same manner as in Example 1 using a container whose entire inside was made of AlN. The sintered body has AlN as the main phase and Y-Al-O as the sub-phase.
There was a large amount of ternary compound phase. The Y content in the sintered body is 19000 ppm, the oxygen content is 14000 ppm, and the density is 3.
It had a low value of 352 g / cm ³ , an average particle size of 12 μm, and a thermal conductivity of 160 w / mK.

Comparative Example 2 An AlN degreased body obtained in the same manner as in Example 1 was manufactured in the same manner as in Example 1 using a container whose entire inside was made of tungsten to manufacture an AlN sintered body. The sintered body had AlN as a main phase and a large amount of Y-Al-O ternary compound phase as a sub-phase. The Y content in the sintered body is 20000 ppm, the oxygen content is 15000 ppm,
Density is 3.360g / cm ³ , average particle size is 11μm, thermal conductivity is 152w
It was a low value of / mK.

The importance of firing in carbon can be seen from such a comparative example.

〔The invention's effect〕

As described above, the aluminum nitride sintered body of the present invention is AlN
Phase and main phase, (rare earth element) -C based compound phase and /
Alternatively, it contains a trace amount of (rare earth element) -O-based compound phase and has excellent properties such as high purity and uniformity and high thermal conductivity, and its industrial value is extremely large. .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiko Sato 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Within Toshiba Research Institute, Inc. (56) References JP 62-252374 (JP, A) JP 62-246867 (JP, A)

Claims (3)

[Claims] 1. An AlN phase as a main phase, containing a rare earth element-C-based compound phase as a subphase, the rare earth element content is 4000 ppm or less, the impurity oxygen content is 3000 ppm or less, and the density is 3.255.
g / cm ³ at ~3.285g / cm ^3, the high thermal conductivity of aluminum nitride sintered body thermal conductivity, characterized in that it is 180 W / m · k or more. 2. The high thermal conductivity aluminum nitride sintered body according to claim 1, wherein the AlN crystal grain size of the sintered body is 3 μm or more. 3. The high thermal conductivity aluminum nitride sintered body according to claim 1, wherein the total amount of impurity cation elements excluding rare earth elements is 1000 ppm or less.