JPH01239067A - Production of aluminum nitride base - Google Patents

Abstract

PURPOSE:To obtain a dense and flat AlN base having high thermal conductivity and high transparency free from warpage and undulation, by calcining green sheets of AlN or a laminate thereof under negative pressure in the presence of Al vapor. CONSTITUTION:Green sheets of AlN or a laminate thereof is calcined under especially preferably 0.2-200mbar negative pressure in the presence of Al vapor. The calcining temperature is 1,600-2,000 deg.C and retention time is preferably 6-12hr. AlN bases thus obtained are further subjected to HIP treatment under the highest pressure of >=10 atmospheric pressure at 1,600-2,000 deg.C to improve characteristics of AlN bases. Since the AlN bases are calcined under negative pressure, a liquid phase is completely vaporized and consequently sintering by treatment under high pressure is smoothly advanced.

Description

[Detailed description of the invention] [Summary] Dense, highly translucent, and flat AβN with high thermal conductivity
Regarding the manufacturing method of the substrate, warping and cracking occur in the substrate due to the decomposition of AIN under normal pressure, and to prevent this, if BN SEC- is alternately layered with AlN green sheets or laminates, the surface of the AIN sintered body will be With the aim of solving the problems of BN diffusion and variation in shrinkage rate within the substrate, and providing a flat, dense, highly transparent, and highly thermally conductive /IN substrate, we developed an AlN green sheet or its A method of firing a laminate under negative pressure and in the presence of aluminum vapor, and further comprising HI
This is configured as a method for P processing.

[Industrial application field]

The present invention relates to a method for manufacturing an aluminum nitride (Aj2N) substrate, and more particularly to a method for manufacturing an AlN substrate that is dense, highly transparent, has high thermal conductivity, and is flat (without warping).

[Prior art and problems to be solved by the invention] The thermal conductivity of AβN single crystal is 320 W/mk in theory, which is higher than that of metal A!
higher than However, the thermal conductivity of the sintered body (polycrystalline body) actually obtained is only about half of the theoretical value. This is due to impurities contained in the raw material powder, especially oxygen impurities, Si, and Fe.

It is believed that metals such as Ca are the cause. So far, Ca compounds such as CaO, which have the function of removing oxygen impurities, and y203 have been added as sintering aids, and H2
Efforts have been made such as firing in a reducing atmosphere such as or C○. However, the obtained sintered body contains impurities of AβN.
In many cases, there is solid solution within the grains or a thick grain boundary phase is formed (this results in brown coloration and low translucency. Therefore, the thermal conductivity remains at a low value as mentioned above. .

AIN substrates are generally created using the pressureless sintering method, but in addition to the firing temperature, heating rate, and firing atmosphere, it is important to consider how the green sheet or green sheet laminate is set in the furnace. be.

Usually, it is placed in a graphite container and fired, but in this case, it has been proposed to spread AIN powder inside the graphite container. However, the AfNl plate has 1
Since the firing is performed at a high temperature of 800° C. or higher, AAN decomposes in nitrogen at 1 atm, causing problems such as warping.

As far as the inventor knows, the BN setter and AβN green sheets or green sheet laminates are alternately stacked, as disclosed in JP-A-62-100479.
The method of firing in a container is highly effective in obtaining a dense AIN sintered body and in eliminating warpage and waviness. However, in this case, there are problems such as diffusion of BN being observed on the surface of the AIN sintered body and large variations in shrinkage rate within the substrate. This means that it is not possible to obtain a complex sintered body in which internal wiring or surface wiring is applied to the green sheet or green sheet laminate, or a Bayer hole is formed.

Therefore, in view of the above-mentioned problems, the present invention has been developed to provide a flat A! that is dense, has high thermal conductivity, is highly transparent, and has no warping or waviness. The purpose is to provide an IN substrate.

[Means to accomplish the task]

The present invention was obtained as a result of studying firing conditions and firing atmosphere in order to achieve the above object. Specifically, the present invention is characterized by firing under a negative pressure of 1 atmosphere or less, and furthermore, Firing is performed by increasing the partial pressure of Aβ vapor pressure. As a result, there is no warping or waviness even without a load from a BN setter, the shrinkage rate is constant within the substrate, and a dense sintered body with high translucency can be obtained. moreover,
The AIN substrate obtained by firing in this manner is subjected to HIP treatment to provide an AβN substrate with further improved properties.

That is, the present invention further provides a method for producing an aluminum nitride substrate, characterized in that an aluminum nitride green sheet or a laminate thereof is fired under negative pressure and in the presence of aluminum vapor, and a sintered body obtained by the above method. A method for manufacturing an aluminum nitride substrate, characterized by performing HIP treatment at a maximum pressure of 10 atm or more and a temperature of 1,600 to 2,000°C.

The manufacturing method of the AIN green sheet and its laminate can be the same as the conventional one, but the sintering aid included in the AβN green sheet is an aluminate that is relatively easy to form a liquid phase and easily evaporates. is desirable.

The firing may be performed at a firing temperature and under negative pressure, and it is preferable to use nitrogen gas as the atmospheric gas, but an inert gas such as argon or a mixed gas of an inert gas and nitrogen gas may also be used. By firing under negative pressure, continuous loss removal of liquid phase becomes more complete. The preferred pressure is (
That is, the initial pressure is in the range of 0.02 to 500 mbar, more preferably 0.02 to 200 mbar, even more preferably 0.2 to 200 mbar. If the negative pressure is small (high pressure), the volatilization of the liquid phase will be insufficient, and if the negative pressure is too large (pressure is small), the decomposition of AAN may not be suppressed, so a pressure within the above range is preferable.

In the present invention, the presence of aluminum vapor pressure is essential in addition to the above-mentioned firing under negative pressure. The presence of aluminum vapor pressure suppresses the decomposition of AAN even during firing under negative pressure, so warping, waviness, and even cracking of Aj2N is effectively prevented. To eliminate the presence of aluminum vapor, it is sufficient to place a powder such as AIN or AN in the furnace. However, AJN and Aβ may be added to the sample (AIN substrate) like packing powder.
It is inappropriate to bring such powders into contact with each other because such powders may adhere to the sample.

The amount of AlN, A, and ff is preferably 100 g or more per 500 β of furnace volume.

In particular, 100g or more of AIN powder per 5001 furnace volume is placed near the sample, and the initial pressure (pressure at room temperature) is 0.2.
Preference is given to firing under nitrogen pressure of ~300 mbar.

The firing temperature is generally in the range of 1,600 to 2,200°C, preferably 1,800 to 2,000°C, and the holding time is generally in the range of 1 to 2,000°C.
20 hours, preferably 6 to 12 hours.

The AIN substrate thus obtained is dense, transparent, and has high thermal conductivity, and has no warpage or waviness.

Furthermore, according to the present invention, the Aβ obtained in this way
By subjecting the N substrate (sintered body) to a maximum pressure of 10 atm or higher, preferably 100 to 1000 atm, and a temperature of 1600 to 2000°C, preferably 1700 to 1900'CT:HIP, the properties of the AffN substrate are improved. be able to. Since the AfNJJ plate fired by the method of the present invention is fired under negative pressure, the liquid phase is completely volatilized, and as a result, sintering by processing under high pressure progresses effectively. Therefore, the /IN
The initial characteristics of the substrate are those of AβN that was HIP-treated after firing using the conventional method.
It has characteristics that are significantly superior to the original characteristics of the substrate.

The atmosphere for the HIP process is preferably nitrogen gas, but even at this time, if necessary, a small amount of AIN or AN powder may be placed to make A6 vapor exist. The holding time is about 1 to 20 hours, preferably about 4 to 15 hours.

An example of how to sinter an AIN green sheet or a laminate thereof and perform HIP treatment of an AIN sintered body according to the present invention will be described with reference to FIG. As shown in the figure, AAN powder 3 and graphite powder 4 are placed in a graphite crucible 2 in a furnace equipped with a heater 1, and placed near a sample 6. Sample 6 is set using graphite safeter 5. Such a furnace is filled with nitrogen, heated and fired under negative pressure, or HIPed under excess pressure.

[For production]

By firing under negative pressure, continuous loss removal of the liquid phase is promoted, making it possible to carry out HIP treatment effectively, and A
AIN even under negative pressure by combined use of N vapor
decomposition can be suppressed.

〔Example〕

■C is added to commercially available AβN powder (manufactured by Tokuyama Sorta) as a sintering aid.
Add 4ivt% of aCO3 and mill with a resin ball using 180g of ethanol and 80g of acetone as solvents.
I went for 4 hours. Next, to 100 parts by weight of this mixed powder, polyvinyl chloride (BL-
1) 6.5 parts by weight and double parts of polyethylene glycol fatty acid ester as a dispersant were added, and milling was further performed for 24 hours.

The obtained slurry was made to a thickness of 250 mm using the doctor blade method.
It was made into a green sheet. Green sheet press pressure 6
Ten sheets were laminated at 0 MPa. This laminate was heated to N, medium 600
C. for 4 hours to remove organic components.

Next, 100 g of AlIN powder was placed in a graphite heating element furnace having an effective volume of 500 j2, and the /IN laminate was placed on a BN setter and fired without applying any load.

For firing, the temperature was raised to 1800℃ at 600'C/h, and the temperature was increased to 180℃.
0°C was maintained for 10 hours. Inside the furnace is 20mba at room temperature.
Filled with r N2 gas and heated at 1800℃ and approximately 100mbar
And so.

The substrate after firing has no warpage or waviness, and has a relative density of 99.5.
% or more, the translucency was also large. The thermal conductivity of the substrate is 220
W/mk and bending strength of 350 MPa.

■Shi = A green sheet laminate was prepared in the same manner as in Example 1, and 1800
Firing was carried out at a temperature of 10 hours. Gas filling at room temperature was between 0.002 and 200 mbar.

The results are shown in the table below.

N1 A green sheet was prepared in the same manner as in 1, and heated to 1800°C.

Firing was performed for 10 hours. Gas filling pressure at room temperature is 20r
It was @bar. Place A ff NFA powder in the furnace
~500 g. The results are shown in the table below.

↓ The sintered body obtained in Example 2 was subjected to HIP treatment. HIP condition is 12
The temperature was raised to 00° C. under vacuum, and then N2 gas was filled in at 1800° C. to a pressure of 200 atm. Further, the holding time at 1800°C was 5 hours. The sample was coated with resin-containing carbon, and a small amount of AIN powder was added into the container.

The results are shown in the figure below.

- A green sheet laminate was produced in the same manner as in Example 1 and degreased. This sample was (1) placed in a vacuum.

(2) 1 mbar Nz gas flow, (3) 1 atm N2 gas flow, (40 atm N2 gas filled, (5)
It was fired at 1800° C. for 4 hours under 10 atmospheres of N2 gas.

The results are shown in the table below. Next, after firing the above samples (2) to 5), H was heated in the same manner as in Example 4.
IP processed. However, during HIP processing, AI! No N powder was used.

The results are shown in the table below.

〔Effect of the invention〕

According to the method of the present invention, there are the following effects.

(1) A uniform and flat substrate can be obtained without applying any load.

(2) Evaporated components can be efficiently removed and decomposition of AfN can be prevented, and a sintered body that is dense, has high translucency, and high thermal conductivity can be obtained.

(3) Enables characteristics to be significantly improved by HIP processing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the firing and HIP processing according to the present invention. DESCRIPTION OF SYMBOLS 1... Graphite heater, 2... Graphite crucible, 3... AIN powder, 4... Graphite powder, 5... Graphite setter, 6... Sample.

Claims (2)

[Claims] 1. A method for producing an aluminum nitride substrate, comprising firing an aluminum nitride green sheet or a laminate thereof under negative pressure and in the presence of aluminum vapor. 2. A method for manufacturing an aluminum nitride substrate, characterized in that the sintered body obtained according to claim 1 is subjected to HIP treatment at a maximum pressure of 10 atmospheres or more and a temperature of 1,600 to 2,000°C.