JP2628598B2 - Manufacturing method of aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for producing a high thermal conductivity aluminum nitride sintered body, which aims to obtain a high thermal conductivity aluminum nitride sintered body by effectively removing impurities in a raw material aluminum nitride. The aluminum nitride powder compact is fired in a nitrogen gas stream under a negative pressure, and then subjected to a HIP treatment to produce a method for producing an aluminum nitride sintered body.

[Industrial applications]

The present invention relates to a method for producing an aluminum nitride sintered body,
In particular, the present invention relates to a method for manufacturing an aluminum nitride sintered body having a high thermal conductivity suitable as a semiconductor chip mounting substrate.

[Problems to be solved by conventional technology and invention]

The thermal conductivity of aluminum nitride (AlN) single crystal is 320 W / mK in theory, which is higher than that of metallic aluminum (Al). However, the thermal conductivity of the sintered body (polycrystal) actually obtained is
140 to 260 W / mK, which is about half of the theoretical value. This is attributed to impurities contained in the raw material powder, particularly oxygen impurities, and metals such as Si, Fe, and Ca. So far, CaO and other C that have the function of removing oxygen impurities
aAddition of a compound or Y ₂ O ₃ as a sintering aid, H ₂ or C
A device such as firing in a reducing atmosphere such as O is employed. However, in many cases, the obtained sintered body has a solid solution of impurities in AlN grains or a thick grain boundary phase formed, and thus is colored brown or has low light-projecting property. As a result, the thermal conductivity remains at 140-260 W / mK.

AlN substrates are generally manufactured by atmospheric pressure firing in a nitrogen gas flow in a tunnel furnace. However, since firing is performed at a high temperature of 1800 ° C or higher, AlN decomposition occurs in a 1 atm nitrogen flow, and warpage occurs. Problem arises. AlN to reduce decomposition
There is a method of burying and baking with powder, but in this case, AlN powder adheres to the substrate and the surface becomes rough. In addition, there is a method in which a weight member is placed and fired in order to suppress warpage. In this case, however, variation in shrinkage ratio, cracking, and the like are likely to occur.

Decomposition hardly occurs when firing in a high-pressure nitrogen atmosphere, but since the liquid phase generated by the reaction with the sintering agent does not volatilize sufficiently, it does not densify and has low thermal conductivity.

Therefore, an object of the present invention is to provide a method for significantly improving the thermal conductivity of an AlN sintered body.

[Means for solving the problem]

The present invention, in order to achieve the above object, after firing the AlN powder compact in a nitrogen stream under a negative pressure of 800 mbar or less,
The obtained AlN sintered body is further heated to a temperature of 1600 to 1900 ° C.,
Provided is a method for producing an AlN sintered body, which is characterized in that HIP processing is performed in the presence of 300 atm and aluminum vapor pressure.

The present inventors have studied to improve the thermal conductivity of the AlN sintered body by performing the HIP treatment,
In the case of pre-baking at a pressure of 1 atm or more, the liquid phase generated by the reaction with the sintering aid does not volatilize sufficiently, the densification is insufficient, and the thermal conductivity does not improve as expected. Impurity volatilization is completed when performed under negative pressure, and the effect of HIP treatment can be greatly improved.Also, the problem of decomposition of AlN by firing under negative pressure is as large as under normal pressure even under negative pressure. It has been found that this is the same, and that it can be supplemented by performing the HIP treatment in the presence of aluminum vapor pressure, and has completed the present invention.

As the AlN powder compact of the present invention, a conventional one used for producing an AlN sintered body can be used, and any of a green compact and a green sheet degreased can be used. Furthermore, according to the method of the present invention, since the calcination is performed under a negative pressure, the degreasing is performed only at a high temperature. Further, the green sheet may be one for forming a semiconductor substrate on which a metallized layer is formed.

The calcination under a negative pressure is performed in a nitrogen stream in order to effectively remove the volatilizing gas.
/ min, preferably about 20 to 40 / min.

The negative pressure here is below 800 mbar, preferably between 60 and 800 mbar. The lower the pressure, the more effectively impurities other than AlN can be removed. However, in order to prevent the decomposition of AlN, 60mba
It is desirable that the pressure be equal to or higher than r.

Firing under negative pressure N ₂ gas stream is generally 1700 to 1800 ° C., carried out over 8 hours.

By firing under negative pressure, an AlN fired body having higher transparency than before can be obtained.

After firing under negative pressure, the obtained AlN sintered body is greatly densified by performing the HIP treatment, the transparency is further increased, and the thermal conductivity is greatly improved.

The conditions of the HIP treatment are 1600 to 1900 ° C., preferably 1700 to 1
800 ° C, more preferably 1750-1800 ° C, 100-300
It is performed in a nitrogen atmosphere under a pressure of atmospheric pressure. Note that an inert gas such as Ar, He, or Ne or a mixed gas of these inert gases and N ₂ is also used. At this time, Al or AlN or the like is used to make aluminum vapor exist in the HIP furnace, and carbon powder is used to further increase the vapor pressure of C if necessary.
Place near the sintered body without contacting the AlN sintered body.
Further, although not limited, it is preferable to be under a vacuum up to, for example, about 1200 ° C. during the temperature rise for performing the HIP treatment since adsorbed oxygen can be removed.

(Operation)

The AlN under negative pressure of N ₂ gas stream can be effectively remove impurities by sintering, which the effect of HIP treatment is enhanced by HIP treatment in the presence of Al vapor pressure, high purity, A dense, high-thermal-conductivity AlN sintered body can be obtained.

〔Example〕

Example 1 1.5 wt% in terms of CaO. A compact of φ12 × 10 mm was formed using AlN to which CaCO ₃ was added.

The resulting green compact was placed in a batch furnace under a negative pressure of 100 mbar and N ₂
The firing was carried out at 1800 ° C. for 6 hours under a flow of a gas of 20 / min. This fired body was excellent in transparency.

This sintered body was subjected to HIP processing. Under HIP conditions, the temperature was raised in a vacuum up to 1200 ° C., and then N ₂ gas was sealed at 1800 ° C. to 200 atm. The holding time at 1800 ° C. was 5 hours. At this time, in the HIP furnace, graphite and AlN powder were placed near the sample in order to increase the partial pressure of C and Al. The situation at this time is shown in FIG. In FIG. 1, reference numeral 1 denotes a graphite heater. Reference numeral 2 denotes a graphite crucible containing an AlN powder 3 and a graphite powder 4. 5 is a grite setter,
The AlN sintered body sample 6 is placed on the graphite setter 5. By performing HIP processing in such a furnace, the vapor pressures of Al and C are maintained in the furnace.

The thermal conductivity of the obtained sintered body was measured by a laser flash method. The results were as follows.

Example 2 (Comparative Example) The same sample as in Example 1 was fired at 1 atm in a N ₂ gas flow of 20 / min. Also in this case, the holding time at 1800 ° C. was 4 hours.

 The HIP conditions were the same as in Example 1.

 The thermal conductivity of the obtained sintered body is as follows.

Comparison between Example 1 and Example 2 shows that firing under negative pressure caused HI
It is recognized that the effect of the P treatment has been enhanced.

Example 3 The same sample as in Example 1 was fired under the same conditions as in Example 1. However, the holding time at 1800 ° C. was 9, 18 and 36 hours.

 The thermal conductivity of the obtained sintered body is as follows.

It is recognized that the thermal conductivity of AlN is improved by 25% or more by performing the HIP treatment after firing under negative pressure instead of the conventional firing under normal pressure.

〔The invention's effect〕

AlN can greatly improve the thermal conductivity of the AlN by HIP treatment after firing with N ₂ gas stream negative pressure, also can be enhanced compactness and purity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state of HIP processing in an embodiment of the present invention. 1 ... graphite heater, 2 ... graphite crucible, 3 ... AlN powder, 4 ... graphite powder, 5 ... graphite setter, 6 ... AlN fired body sample.

Continued on the front page (72) Inventor Table Koji 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Nobuo Kamehara 1015 Uedanaka, Nakahara-ku, Nakazaki-ku Kawasaki City, Kanagawa Prefecture Fujitsu Limited (56) Reference Document JP-A-1-167279 (JP, A)

Claims (1)

(57) [Claims] After firing an aluminum nitride powder compact in a nitrogen stream under a negative pressure of 800 mbar or less, the obtained aluminum nitride sintered body is further heated to a temperature of 1600 to 1900 ° C. and 100 to 3900 ° C.
HIP under the pressure of 00 atm, in the presence of aluminum vapor pressure
A method for producing an aluminum nitride sintered body, characterized by performing a treatment.