JP2560438B2 - Method for manufacturing aluminum nitride substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A method for manufacturing an aluminum nitride substrate, for the purpose of manufacturing an aluminum nitride substrate having high purity and excellent mass productivity, placing and firing a green sheet made of aluminum nitride. The firing jig was made by nitriding a firing jig made of fused alumina, and the surface of which was altered to aluminum nitride was used.The green sheet was placed on the alteration jig and fired in a nitrogen stream. This constitutes the method for manufacturing the aluminum nitride substrate.

[Industrial applications]

 The present invention relates to a method for manufacturing an aluminum nitride substrate.

Information processing devices have been downsized and increased in capacity because of the need to process a large amount of information quickly, and the semiconductor devices that make up the main components of these devices are becoming more integrated, and LSIs and VLSIs are being put to practical use.

Here, the integration is performed by miniaturizing the unit transistor, and the minimum width of the conductor line is about 1 μm.

On the other hand, the current of the unit transistor is
Since it is turned off, the amount of heat generated increases as the degree of integration increases, and the power consumption reaches 10 W for a 10 mm square chip.

Therefore, the amount of heat generated by a multilayer wiring board on which a large number of such LSI chips are arranged and mounted is enormous.

Here, in order to operate the semiconductor device reliably and stably, the temperature of the semiconductor chip should be 85 ℃ or less, 100 ℃ at the maximum.
It is necessary to keep below.

Therefore, it is necessary that the substrate constituting the multilayer wiring board has excellent heat resistance and thermal conductivity.

[Conventional technology]

An alumina (α-Al ₂ O ₃ ) ceramic substrate has been conventionally used as a substrate on which a semiconductor chip such as an LSI or VLSI is mounted, and a cooling structure is considered based on this substrate.

That is, LSI chips are arranged in a matrix on a multilayer ceramic substrate made of alumina, and bellows are provided on each chip instead of fins provided for air cooling, and water is circulated in the bellows to form the chips. It is being cooled.

Further, a method of making a sealed structure having a multilayer ceramic substrate as a bottom surface and circulating a low boiling point refrigerant in the structure to forcibly cool it has been attempted.

Here, the thermal conductivity of alumina ceramic substrates is superior to that of glass ceramic substrates.
It is about W / mk, and in order to prevent the temperature rise of the semiconductor chip, it is necessary to change the substrate material and increase the heat radiation amount through the substrate.

Here, aluminum nitride (AlN) is a ceramic with excellent heat resistance and thermal conductivity.

This AlN has the property of sublimating at high temperatures, and its melting point is 3000 ° C or higher when measured under ultrahigh pressure conditions, and it is a stable nitride.

The thermal conductivity is 260 W / mk (theoretical value 320 W / mk) and α-Al ₂ O
The thermal conductivity of ₃ is 20 W / mk, which is significantly higher than that of 3.

Therefore, AlN ceramic substrates are being put into practical use.

Next, as a method of making an AlN ceramic substrate, there is a hot press method in which AlN powder is molded and is baked under high pressure. However, this method is inferior in mass productivity and has a high accuracy in terms of pattern accuracy. It is impossible to make a substrate.

Therefore, a method in which a sintering aid is added to AlN powder to make a green sheet and fired is practical, and this method has been studied.

As a result of further research, yttrium oxide (Y ₂ O ₃ ) and calcium oxide (CaO) are suitable as sintering aids, and since sintering is performed at a high temperature of over 1900 ° C, the purity and density are high. It is well known that the selection of a firing jig (hereinafter abbreviated as a setter) and the method of arranging the green sheets are important in order to obtain a ceramic substrate that does not warp.

That is, when firing a material having a firing temperature of more than 1800 ° C., it is preferable to use a furnace in which a heat insulating material, a heating element, etc. are fired using graphite (graphite) and to fire the fired sample in a graphite container. As is customary, when the AlN green sheet is fired using this method, the sintering aid contained in the green sheet is reduced by graphite.

Therefore, a method of covering the inside of the graphite container with powder of AlN or boron nitride (BN) is adopted.

In addition, as a method to obtain a flat AlN substrate, BN setter and A
lN green sheets are alternately stacked, placed in a BN container and fired.

However, in this method, BN is diffused on the surface of the AlN substrate to cause contamination, and it is easy to produce a substrate with warpage or "waviness" due to large shrinkage at the four corners of the green sheet. There's a problem.

[Problems to be Solved by the Invention]

As mentioned above, AlN substrates are attracting attention because of their high thermal conductivity and excellent heat resistance, and they are being put into practical use, but to develop a method for obtaining flat substrates that are free from contamination and deformation. Is an issue.

[Means for solving the problem]

As a setter for mounting and firing a green sheet made of AlN, the above-mentioned problem uses a furnace in which a firing jig made of fused alumina is nitrided and the surface of which is changed to AlN.
The green sheet is placed on top of the setter, N ₂
This can be solved by firing in an air stream to produce an AlN substrate.

[Action]

The present invention is to obtain a smooth and stable setter by nitriding the surface of fused alumina as a setter and using the one whose surface is modified to AlN.

That is, by placing a green sheet made of AlN on the AlN setter, it is possible to eliminate contamination due to diffusion of different elements.

Here, it is possible to fuse the two during firing.
As described above, AlN melts for the first time at a temperature of 3000 ° C or higher under ultrahigh pressure, so that it is stable and does not cause fusion at a temperature of about 1900 ° C.

Further, since graphite and BN do not come into direct contact with the green sheet, neither contamination nor reduction of the sintering aid occurs.

The thickness of AlN formed on the fused alumina must be at least 500 μm or more, preferably 1 mm or more, because the reason is to prevent the fused alumina from diffusing to the surface during the firing treatment. The nitriding condition for making AlN is that the treatment temperature is 1800 to 2050 ° C, preferably 1900 to 2000, as a result of experiments.
℃, N _{2 as} a gas pressure of 10 Kg / cm ² preferably 100 Kg /
cm ² required.

Further, as a firing condition of the AlN green sheet to be placed and fired on the setter thus formed, the maximum temperature is 1800 to 1950 ° C, preferably 1850 to 1900 ° C,
It is advisable to perform firing while flowing N ₂ gas at a flow rate of 1 m ³ / h or more at 1 atm.

[Example] Example 1: (Manufacturing example of setter) A smooth fused alumina substrate having a size of 100 x 100 mm and a thickness of 10 mm was prepared, and BN was used as a spacer in a graphite container as shown in Fig. 2. Stacked as.

That is, a BN spacer 3 is placed on the bottom of a graphite container 2 having a plurality of holes 1 on its side surface, a fused alumina substrate 4 is placed on the BN spacer 3, and the BN spacer 3 and the fused alumina substrate 4 are placed as shown in FIG. The lid 5 made of graphite was alternately stacked in five layers, and the container 2 was set in a pressure firing furnace.

First, after thoroughly replacing the inside of the furnace with N ₂ gas, 100 K at room temperature
It was sealed until the pressure reached g / cm ² , and the temperature was raised to 1950 ° C. over 4 hours.

At this time, the pressure in the furnace at 1950 ° C was 500 Kg / cm ² .

Then, after keeping this state for 6 hours, the surface of the fused alumina substrate 4 is cooled to room temperature to a thickness of 1 mm.
Formed AlN.

Observation of the fractured surface of this nitrided fused alumina with a scanning electron microscope (SEM) and an X-ray microanalyzer (XMA) showed that Al and N were observed with a strength of 1: 1 from the surface to a thickness of about 1 mm, and oxygen was observed. The presence of (O) was not recognized.

Example 2 (Production Example of AlN Substrate) Calcium carbonate (CaCO ₃ ) was added as a sintering aid in an amount of 2% by weight in terms of CaO to AlN powder having an average particle size of 1 μm, and 100 g of this ceramic powder was mixed with an organic binder. Polyvinyl butyral (abbreviated as PVB) 12g is added as this, alcohol and acetone are added as a solvent to this, and it is kneaded with a ball mill for 50 hours to form a slurry.
A μm green sheet was formed.

Ten green sheets were laminated to form a laminated body having a thickness of 1 mm, and the laminated body was heated and degreased in wet N ₂ at 600 ° C. for 9 hours.

FIG. 1 shows a method of firing the AlN laminate formed in this way. The setter 6 made in Example 1 is placed on the bottom of the graphite container 2 via the BN spacer 3 and the AlN green sheet is placed on top of this. 7 was placed.

Then, the BN spacer 3 was placed in the corner of the setter 6, the setter 6 and the green sheet 7 were placed thereon as shown in the same figure, and this was repeated three times, and the lid 5 made of graphite was used as in the conventional case.

Then, while flowing N ₂ under the condition of 1 atm and 10 / min, 1900
A multilayer substrate was prepared by firing at 10 ° C for 10 hours.

When the density, thermal conductivity and warpage were measured, excellent values as shown in Table 1 could be obtained.

The density of 3.246 corresponds to a relative density of 99.6%.

〔The invention's effect〕

According to the present invention, it is possible to mass-produce an AlN substrate that is dense, has high thermal conductivity, is free from contamination, is flat, and has no warp.

[Brief description of drawings]

FIG. 1 is a sectional view showing a method for manufacturing an AlN substrate according to the present invention, and FIG. 2 is a sectional view showing a method for manufacturing a setter according to the present invention. In the figure, 2 is a graphite container, 3 is a BN spacer, 4 is a fused alumina substrate, 5 is a lid, 6 is a setter, and 7 is a green sheet.

Claims (1)

(57) [Claims] 1. A method for producing an aluminum nitride substrate, comprising placing a green sheet made of aluminum nitride on a firing jig of fused alumina whose surface is nitrided, and firing it in a nitrogen stream.