JPH03146471A - Production of aluminum nitride sintered body - Google Patents

Abstract

PURPOSE:To obtain a sintered body having high heat conductivity by preparing and molding aluminum nitride powder mixed with a specified sintering aid and sintering the molded body within a specified temp. range in a nonoxidizing atmosphere. CONSTITUTION:Aluminum nitride powder mixed with 0.5-6wt.% one or more kinds of oxides selected among the oxides of Y, Sc and lanthanoids as sintering aids and 0.01-3wt.% one or more among LaB6, MgB6 and CaB6 is prepd. and molded. This molded body is sintered within the temp. range of 1,600-2,000 deg.C in a nonoxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method for producing an aluminum nitride sintered body, and particularly to a method for producing a high thermal conductivity aluminum nitride sintered body, which is highly demanded in industry.

[Prior Art] High thermal conductivity AfiN sintered bodies are specifically used as insulating materials, typically semiconductor substrate materials. With the trend toward higher integration, higher speed, and higher output of semiconductors, the following problems have come into focus. In other words, ■ How to efficiently release the heat generated by the semiconductor chip to the outside of the system.

■ As operational precision improves, signal delays in the substrate or package become a problem.

■ As the chip size increases, the difference in thermal expansion coefficient between the chip and the chip increases, reducing signal reliability.

■ As the voltages used in high-power chips continue to increase, dielectric breakdown of substrates is becoming a problem.

Ceramics for substrates or packages that can replace conventional alumina and solve these problems faced by semiconductors include (a) high thermal conductivity;

(b) Excellent electrical insulation.

(c) Good high frequency characteristics (low dielectric constant, low dielectric loss) (d) The coefficient of thermal expansion is close to that of Si or GaAs.

(e) Chemically stable.

(f) High mechanical strength.

(g) Circuit formation is easy.

(h) Can be airtightly sealed.

It is desirable to have the following characteristics. Al2N is considered to be promising as a material basically having such characteristics.

However, when attempting to specifically apply Al2N ceramics, it is necessary to satisfy the following minimum characteristics. That is, (1) the sintered body is uniform and dense. It is desirable that the mechanical strength is high and the relative density is 95% or more.

(2) High thermal conductivity.

(3) Volume resistance is high (≧1Q12Ω·cm) (4) The surface of the sintered body after firing is smooth and flat.

(5) The appearance of the sintered body shall be uniform in color and without unevenness or coloring.

Although item (4) above is not required,
If the surface roughness of the fired sintered body is greater than 0.5 μm, surface processing is required.

Therefore, when manufacturing substrates in large quantities, item (4) becomes important from the viewpoint of reducing manufacturing costs. Further, item (5) is also the same as (4). That is, after forming a circuit on an AgN substrate, it is necessary to inspect the circuit. If there is an abnormality such as coloring on a part of the surface of the Al2N substrate, it not only spoils the product image but also makes circuit inspection difficult and effectively eliminates the product value. In addition, a mesh pattern may occur on the surface of the substrate. The mesh pattern is an aggregation of small pores, which also reduces the strength of the substrate.

Therefore, the Al2N substrate is required not only to have high thermal conductivity, but also to have a low surface roughness after baking, and to have a -like color tone without any abnormalities in appearance such as coloring or mesh patterns on the surface of the substrate. ing.

In conventional techniques, in order to satisfy the above characteristics (1) and (2), Y2 oa is used as a sintering aid as shown in Japanese Patent Publication No. 46-41003, or As shown in the publication, Cab, B
Using aO%SrO etc. as a sintering aid, the thermal conductivity is 1.
Ceramics with a power rating of about 00 W/m- are used.

In addition, the journal of the Ceramics Industry Association, the 25th Ceramics Industry Basics Forum, IDO3
, 3HO3 (January 1985) shows a method for obtaining an Al2N sintered body with high thermal conductivity by sintering a /MAN compact at 1850 to 1950°C for 2 to 96 hours in a reducing atmosphere. There is. This method has a problem in that the manufacturing cost is high because the once fired substrate is refilled in a graphite crucible and fired again.

On the other hand, Japanese Patent Application Laid-Open No. 62-52181 discloses a molded body containing 0.2 to 3.4 parts by weight of carbon and 0.1 to 10 parts by weight of yttrium oxide as sintering aids in AβN. A characterized by sintering at 1600-2100°C
A method for manufacturing a βN sintered body is disclosed. However, the maximum thermal conductivity is only about 140 W/m-.

The thermal conductivity of a single crystal of Al2N is said to be 32 ow/m-, and this thermal conductivity is not satisfactory.In addition, these prior art techniques have problems with surface roughness, which is important when handling the substrate as a product. There is almost no mention of the appearance of the board, etc.

[Problem to be solved by the invention 1 The conventional technology using Y2 os as a sintering aid (a) cannot obtain sufficient thermal conductivity (Japanese Patent Publication No. 46-41
(b) In order to obtain sufficient thermal conductivity, the manufacturing cost is high because the fired substrate must be packed back into the graphite crucible and fired again. 25th Ceramics Basics Debate I DO3,3HO
3) (c) There is a problem in that the surface roughness of the baked substrate and the appearance of the substrate surface, which determine the commercial value and manufacturing cost of the AI2N substrate, have hardly been studied.

In order to solve these problems, a new high thermal conductivity Af
An IN substrate was needed.

An object of the present invention is to provide a high thermal conductivity substrate that solves all of the problems (a) to (c) above. That is, (i) it has a thermal conductivity of 170 W/m- or more.

(ii) Adopt atmospheric pressure firing, which is excellent in mass production, and achieve high thermal conductivity through -degree heat treatment.

(iii) When using the Al2N sintered body as a substrate,
Surface roughness (Ra) of baked goods has important meaning
is 0.5 μm or less.

(There is no abnormality such as coloring on a part of the ivlAJ2N board or mesh-like color unevenness.

The present invention provides a technology for manufacturing IN substrates with high commercial value that meet all four criteria through a single heat treatment. The present invention provides a technique that does not require a new process such as polishing the surface of the obtained substrate.

[Means to solve the problem]

In view of the problems of the prior art described above, the inventors of the present invention have conducted repeated research to improve the thermal conductivity of aluminum nitride sintered bodies and provide the necessary characteristics as a substrate, and as a result, the following new matters have been discovered. This discovery led to the present invention.

That is, the present invention provides a sintering aid using one selected from the group of oxides of yttrium, scandium and lanthanoids.
0.5 to 6% by weight of the species or two or more species, and LaB5,
MgB6 and Ca13. 1 or 2 selected from
A mixed powder of aluminum nitride containing 0.02 to 3% by weight of acetic acid or more is prepared, molded, and heated to 1% in a non-oxidizing atmosphere.
This is a method for producing an aluminum nitride sintered body, which is fired in a temperature range of 600 to 2000°C.

Lanthanoids range from La with atomic number 57 to 71 with atomic number
It is a general term for 15 rare earth elements leading to Lu.

According to the present invention, a dense sintered body with excellent thermal conductivity and electrical insulation can be obtained. Also, when fired in the form of a substrate,
There are no abnormalities in appearance such as mesh color unevenness or coloring in some parts on the surface of the substrate, and the surface roughness Ra after baking is 0.
．． An Al2N sintered body with a thickness of 5 μm or less can be obtained.

[Effect]

The sintered body manufactured according to the present invention satisfied all of the items (i) to (iv) required for an insulating substrate.

Based on this fact, the present invention was completed as a result of extensive studies regarding the optimum addition range, other powders, and compounds that meet the above requirements. If the additive element or its compound and its addition range are limited and selected, the relative density will be 95% or more, the thermal conductivity will be 170 W/m or more, the baked surface roughness will be 0.5 μm or less, and the mesh-like An Al2N highly thermally conductive and electrically insulating substrate without any abnormalities in the surface appearance of the substrate such as color unevenness or discoloration of some parts of the substrate can be obtained.

Although the mechanism by which the combined addition of sintering aids according to the present invention is effective has not been fully elucidated, it is thought to be as follows.

The surface layer of Al2N has a complete /l! Even if it is not 203, some kind of AI2 oxide is present. Assuming that this oxide is Al2203, there will be a liquid phase xAff203 between the added sintering aid component, for example Y203.
Generate 3'Y2O3.

On the other hand, all LaB6, MgB6, and CaB6 are compounds that are extremely easily oxidized, in other words, they have a strong reducing effect. For this reason, in a system in which LaB6 is added to Y2 oa, which reacts with and removes impurities in Al2N, firing was performed at 1850° C. for 2 hours so that some liquid phase remained at the grain boundaries. As a result of powder X-ray diffraction, the grain boundary phase of the sintered body was mainly composed of Al22 Y4 os, with a small amount of Y2 oa coexisting. When Y203 is added alone, the grain boundary layer consists of YAG (Ya Al25012) and YAI20.
3 had almost the same X-ray diffraction intensity. From this, the liquid phase composition during sintering is higher in the Y203-LaB6 system than in the Y2
It can be seen that the composition is rich in Y2 oa compared to the oa type. This means that LaB6 is Aff2 o on the surface of AfiN powder.
It acts effectively as a reducing agent in the a-layer, and Aff203 in the liquid phase
This seems to be the result of fewer layers.

Due to the reduction action of LaB6, MgH2, and CaBs during sintering, oxygen on the Al2N surface is reduced and reduced in size during the stages from liquid phase generation to grain growth.
Purify the fN powder. The resulting sintered body is ideal as a highly thermally conductive, electrically insulating substrate.

The effects of adding LaB6, MgH2, and CaB6 are that their own reducing power effectively acts on sintering, resulting in high thermal conductivity, and it is also possible to obtain a substrate with excellent electrical insulation and no uneven coloring.

The details of this effect are not clear.

The addition of LaB6, MgH2, and CaBs effectively acted as reducing agents for Aβ203 on the surface layer of AflN powder, resulting in
It is thought that it will be 203. Since this B2 oa lowers the viscosity of the liquid phase, the liquid phase is uniformly diffused into the sintered body. As a result, the distribution of the liquid phase in the substrate becomes uniform, and it is thought that the sintering of Al2N itself becomes homogeneous. Therefore, sintering progresses uniformly on the inner surface of the substrate, and color unevenness, coloring, etc. are thought to be eliminated.

The amount of one or more selected from the group of oxides of yttrium, scandium and lanthanoids is 0.
．． If it is less than 5% by weight, the thermal conductivity will be low and the properties required for the substrate will not be met.

On the other hand, if it exceeds 6% by weight, the amount of grain boundary phase will be too large and the thermal conductivity will decrease.

Further, if the amount of one or more selected from LaB6, MgH2 and CaB6 is less than 0.01% by weight, a high thermal conductivity of 170 W/m- or more cannot be obtained. In addition, mesh-like color unevenness or coloring tends to occur in a part of the substrate, and the surface roughness after baking is often 0.5 μm or more. On the other hand, if the amount added exceeds 3% by weight, YN remains as a grain boundary phase, and some parts of the substrate are observed to be colored yellow. Furthermore, the shrinkage rate during sintering is so low that it may not be possible to obtain a relative density of 95% or more.

[Example J Example-■ Aj2N powder with an average particle size of 1 μm, Y2O3 powder with an average particle size of 1 μm and LaB with an average particle size of 2 gm in the amounts shown in Table 1
6. MgH2 and CaB6 were added together with a toluene-ethanol mixed solvent, thoroughly mixed and crushed in a ball mill, and then a polyvinyl butyral resin was added as a binder to prepare a /IN slurry.

Using this, a green sheet was created by a doctor blade method and punched into a 65 x 65 mm square to obtain a green molded body.

After degreasing these in N2 at 700°C, they were fired at 1900°C for 3 hours under normal pressure in N2 atmosphere to obtain an AβN substrate.

Appearance and relative density of the obtained A4N board.

Properties such as thermal conductivity, insulation resistance, and surface roughness were measured. The results are shown in Table 1. In particular, when the appearance of the substrate had a mesh-like color unevenness, it was indicated as "mesh", and when coloration occurred in some parts of the substrate, it was indicated as "colored".

According to Examples 1 to 14, 0.5 to 6% by weight of y2oa, L
aB6 to 0. By blending 1 to 3% by weight of O, the thermal conductivity is 170w/m or more, and the insulation resistance is 1Q14Ω'
cm or more, surface roughness Ra < 0.5 μm, relative density 9
A dense sintered body with a density of 5% or more was obtained. Further, when used as a substrate, no abnormalities such as mesh-like uneven coloring or discoloration of some parts of the substrate were observed.

Comparative example! However, when the amount of Y2O3 was less than 0.5% by weight, the thermal conductivity was as low as 135 w/m-. Comparative example 2
When the amount of Y2O3 was more than 6% by weight, the thermal conductivity was low, and in some cases, mesh-like uneven coloring was observed.

In Comparative Example 3.4.5, when the blending amount of LaB6 was less than 0.01% by weight, the thermal conductivity decreased to 170 W/m- or less, and mesh-like coloring unevenness appeared. Also, the surface roughness is 0.5
The thickness was larger than μm, and polishing was required to use it as a substrate.

In Comparative Examples 6 to 11, when the amount of LaB6 exceeded 3% by weight, the appearance of the substrate was colored and some parts of the substrate were colored yellow.

In Examples 15 to 23 and Comparative Examples 12 to 17, MgBs was used instead of LaB6, but it was shown to have exactly the same effect as LaB6.

In Examples 24 to 32 and Comparative Examples 18 to 23, examples were shown in which CaB6 was used instead of LaB5.

These were also shown to have exactly the same effect as LaBe.

Examples 33 to 35 show examples in which two or three of LaBe, MgH2, and CaB6 were added. These also showed excellent properties.

Example-■ In place of the Y2O3 powder in Example-■, 5 with an average particle size of 1 μm was used.
c203 was treated in the same manner as in Example-■, and Al2N
I got the board.

Properties such as appearance, relative density, thermal conductivity, insulation resistance 1 and surface roughness of the obtained AffN board were measured. The results are shown in Table 2. In particular, when the appearance of the substrate had a mesh-like color unevenness, it was indicated as "mesh", and when coloration occurred in some parts of the substrate, it was indicated as "colored". Examples 1 to 32 are excellent in thermal conductivity, relative density, surface roughness, and appearance, while Comparative Examples 1 to 23 are inferior in these.

That is, the use of 5c203 also has the same effect as Y2O3.

Example-■ Using CeO2 powder in place of the Y2O3 powder in Example-4, the same process as in Example-■ was carried out to obtain an Al2N substrate.

Properties such as appearance, relative density, thermal conductivity, insulation resistance, and surface roughness of the obtained Al2N plate were measured. The results are shown in Table 3. "Mesh J" and "Coloring" are the same as in Example-■. Examples 1 to 32 of Example-III, Comparative Example 1
It can be seen that Samples 23 to 23 show almost the same numerical values as Example-2.

Example-■ In place of the Y2O3 powder in Example-I, N with an average particle size of 1 μm was used.
Properties such as appearance, relative density, thermal conductivity, insulation resistance, and surface roughness were measured for the AβN plate treated in the same manner as in Example-■ using d2O3, and the results are shown in Table 4.
It is clear that the use of 03 also produces excellent effects.

Example-V As other sintering aids, D3'203 and Yb2O3, which are oxides of other lanthanoids, were investigated to see the interaction when two or more sintering aids are combined. Two to three kinds of mixed powders were treated in the same manner as in Example-■ to obtain an Al2N substrate.

Appearance and relative density of the obtained Al2N plate.

Properties such as thermal conductivity, insulation resistance, and surface roughness were measured, and the results are shown in Table 5.

All of these characteristics of the IN board showed excellent performance.

〔Effect of the invention】

According to the present invention, the pressureless sintering method with excellent mass productivity is adopted, and 1
High thermal conductivity of more than 170W/m- after firing twice, 1
It is now possible to inexpensively produce an AIN board with high commercial value, which has both high insulation properties of 0.14 Ω·cm or more, is dense, and has no mesh-like color unevenness or coloring in its appearance. According to the method of the present invention, there is no need to provide any other process such as substrate polishing other than honing.

Claims (1)

[Claims] 1. As a sintering aid, 0.5 to 6% by weight of one or more selected from the group of oxides of yttrium, scandium, and lanthanoids, and from among LaB_6, MgB_6, and CaB_6. 0.0% of the selected one or more types.
1. A method for producing an aluminum nitride sintered body, which comprises preparing an aluminum nitride mixed powder containing 0.01 to 3% by weight, molding the powder, and firing it in a non-oxidizing atmosphere in a temperature range of 1600 to 2000°C.