JPH0450171A - Preparation of aln sintered product - Google Patents

Abstract

PURPOSE:To prepare an AlN sintered product having high strength and high thermal conductivity in good productivity by defatting an AlN sintered product containing Y2O3, heating the product under a specific condition in a nitrogen stream and sintering the product under ordinary pressure. CONSTITUTION:A mixture of AlN as a main component and 0.5-10wt.% of Y2O3 as a sintering auxiliary is molded, defatted, heated so as to give a linear shrinkage rate of >=0.2%/hr at temperature of >=1500 deg.C and sintered at 1750-1950 deg.C under ordinary pressure. The further addition of carbon or a com pound producing the carbon on a calcination in an amount of 0.01-0.1wt.% readily gives a high thermal conductivity of >=170W/mK.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a method for producing an AβN sintered body having a room temperature three-point bending strength of 50 kgf/mm” or more and high thermal conductivity.

[Prior Art] In recent years, as the degree of integration of semiconductor elements such as LSIs has increased, the amount of heat generated by LSIs has increased, and it has become necessary to quickly conduct and dissipate the generated heat to the outside.

Furthermore, in substrates and packages on which high-output devices such as power transistors and laser diodes are mounted, heat generated during operation of the device must be released outside the device within a short period of time.

In order to mount such semiconductor elements that generate a large amount of heat, a substrate material with high thermal conductivity is required, and conventionally, beryllium oxide (Bed) is used as an insulating substrate with high thermal conductivity.
) type sintered bodies have been used, but their range of use has been limited due to their toxicity.

Recently, AlN has attracted attention as a highly thermally conductive substrate because it is nontoxic and has high thermal conductivity, and its coefficient of thermal expansion is lower than 8β203 and comparable to that of silicon.

When AlN is used industrially, it is necessary to satisfy the following minimum characteristics. In other words, ■ The sintered body is uniform and dense, and has a high mechanical strength.

■ Thermal conductivity is as high as possible.

■ High volume resistance (>1012Ωcm).

■ The surface of the sintered body made of baked clay is smooth and flat.

■ The appearance of the sintered body is uniform in color with no unevenness or coloring.

A substrate made by bonding a copper plate to an AβN sintered body is a very useful material for removing heat generated from high-power devices.

However, repeated thermal stress occurs on the AlN side of the copper plate bonded substrate. For this reason, repeated use tends to cause problems such as peeling off of the AJ2N board and the copper plate.

To solve this problem, it has been proposed to insert an active metal between copper and AlN to form an intermediate phase in order to alleviate thermal stress (Japanese Patent Application Laid-open No. 32648/1983). In this case as well, tensile stress is generated on the AjZN side. In order to improve the reliability of the copper plate bonded substrate, it is naturally preferable that the AlN substrate itself has a strength large enough to withstand tensile stress. For this reason, a substrate with high thermal conductivity and high strength has been required.

In conventional technology, since AlN is inherently difficult to sinter, Y
A manufacturing method in which a sintering aid such as 2O3 is added has been studied (Japanese Unexamined Patent Publication No. 127267/1983). However, its room temperature three-point bending strength is 30 to 50 kgf/mr.
It was about ``n''.

[Problem to be Solved by the Invention 1] The present invention solves the above-mentioned problems of the prior art, and uses atmospheric pressure firing with excellent productivity to achieve a room temperature three-point bending strength of 50 kgf.
Aβ with high strength and high thermal conductivity exceeding /mrn”
The present invention provides a method for manufacturing a N sintered body.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a mixture in which 0.5 to 10% by weight of Y203 is added as a sintering aid to AlN as a main component, and after shaping and degreasing, 150 in a nitrogen stream
A method for producing an AβN sintered body, characterized by raising the temperature at a linear shrinkage rate of 0.2%/hour or more at 0°C or higher and firing at normal pressure at 1750 to 1950°C, and a sintering aid. The present invention provides a method for producing an AlN sintered body according to claim 1, further comprising adding carbon or a compound that produces carbon upon firing in an amount of 0.01 to less than 0.1% by weight in terms of carbon.

[Function] The present inventors conducted extensive studies to solve the above problem, and found that the starting point of most fractures in AβN sintered bodies is at a diameter of 30 mm.
It was found that the particles were abnormal grain growth particles of um or larger. Therefore, in order to increase the strength of the AlN sintered body, a sintered body composed of fine particles and free of pores is desirable.

As a result of various studies, it was found that extremely fine sintered bodies with an average grain size of about 3 to 5 μm can be obtained by increasing the temperature at a linear shrinkage rate of 0.2%/hour or more at 1500°C or higher during firing. Ta. Linear shrinkage rate is the rate of change of linear shrinkage rate over time. Therefore, the fracture of the sintered body only progresses from the processing scratches on the surface, and the 3-point bending strength at room temperature is 50 kgf/
It now has a strength greater than mrn''.

The present invention will be explained in detail below.

Add 0.5 to 0.5 Y2O3 as a sintering aid to AlN as the main component.
Add 10% by weight. When Y2O3 is less than 0.5% by weight, the amount of liquid phase generated during sintering is small, resulting in insufficient densification and a decrease in thermal conductivity of the sintered body. When the amount added exceeds 10% by weight, the amount of liquid phase is too large, which often causes a decrease in thermal conductivity, and at the same time, yellowing tends to occur in a portion of the substrate.

As a sintering aid, in addition to Y2O3, carbon or a compound that generates carbon by sintering is used as a sintering aid of 0, O1 to 0.1 in terms of carbon.
Less than % by weight can be added.

By adding 0.01 to less than 0.1% by weight of carbon to Y2O3, a high thermal conductivity of 170 W/mK or more can be easily obtained.

If the amount of carbon added is less than 0.01% by weight, virtually no effect of the addition is observed. Furthermore, if the amount of carbon added is 0.1% by weight or more, carbon remains in the sintered body after sintering, causing the sintered body to turn black and at the same time, the thermal conductivity to the contrary decreases, resulting in loss of commercial value.

The atmosphere during firing may be a nitrogen stream, but it is preferable to perform the firing in an atmosphere in which carbon is blocked, for example, in a crucible made of AJ2N. A completely dense body cannot be obtained in a reducing atmosphere such as when firing in a carbon crucible.

During firing, the temperature is increased while controlling the heating rate so that the linear shrinkage rate at 1500° C. or higher is 0.2%/hour or higher. In this case, the AffN sintered body is an extremely fine sintered body with an average grain size of about 3 to 5 μm, and a room temperature three-point bending strength of 50 k
It has a strength of more than "gf/mrn" and a linear shrinkage rate of 0.
If it is less than 2%/hour, large residual pores are generated as grain growth progresses at low temperatures, and these pores are not eliminated during sintering, making it impossible to obtain a dense sintered body. Therefore, only an Aj2N sintered body with low strength can be obtained.

The upper limit of the linear shrinkage rate is not particularly limited, but if the temperature is increased at a large linear shrinkage rate, the temperature increase rate of the compact tends to vary depending on the position in the furnace (the strength of the sintered compact within the same firing lot) It is preferable because the heating power of the firing furnace is large (which makes it uneconomical). Suitable values of 0.2%/hour or more are used.

A method for determining the heating rate so that the linear shrinkage rate during heating becomes a predetermined value will be described. Using a sintering furnace equipped with a thermal dilatometer, the change in shrinkage rate is continuously measured, and while determining the change in the measured shrinkage rate over time, if the shrinkage rate is lower than the set shrinkage rate, increase the heating power and reverse the change. If the shrinkage speed is higher than the set contraction speed, heating may be performed while performing PID control to reduce the heating power.

It is preferable to raise the temperature so that the linear shrinkage rate is constant because the crystal grain size of the sintered body becomes uniform and variations in the strength of the sintered body are reduced.

The sintering temperature is 1750-1950°C.

If the temperature is lower than 1750°C, a complete dense body cannot be obtained.

If the temperature exceeds 1950°C, the particle size of the sintered body increases and the strength deteriorates.

As for the grain boundary composition of the sintered body, it is preferable that Y4Aj2209 and Y2O3 coexist. Y4/1209 and Y2O in the grain boundary phase
When 3 coexists, the thermal conductivity becomes high and the occurrence of abnormalities in appearance is extremely small.

Grain boundary phase is Al2203, YAG phase or YAJ20
When three phases are contained, thermal conductivity decreases.

In addition, coloring tends to occur in the mesh pattern and parts of the board.

Preferable examples of carbon include carbon black and graphite, and examples of substances that generate carbon during firing include phenol resin.

It is preferable that the AlN powder used has an average particle size of about 1 to 2 μm, and the amount of oxygen contained in the powder is less than 2%. Also Y2
03 preferably has a purity of 99.9% or more and an average particle size of 5 μm or less.

〔Example〕

Example 1 Average particle size 0.8 μm, oxygen content 0.6%, purity 98%
The main component is AlN powder with an average particle size of 1. OLL
3% by weight of Y2O3 powder was added.

An appropriate amount of polyvinyl butyral (PVB) was added as a binder and molded, and the molded product was degreased in nitrogen.

Next, the obtained molded body was filled into an Aj2N crucible, and the temperature was raised at a heating rate of 500°C/hour until it reached 1500°C under normal pressure, and after it exceeded 1500°C, various constant linear shrinkage rates were applied. The temperature was raised to 1,820° C. in a nitrogen stream for 4 hours.

The obtained sintered body was made into a test piece 5 with a size of 3 x 4 x 40 mm.
The sintered body was ground to zero and subjected to a three-point bending test in accordance with JISR1601, and the strength variation of the sintered body was expressed as a Weibull coefficient. In addition, thermal conductivity was measured using a laser flash method. Table 1 summarizes the thermal conductivity, strength, and Weibull coefficient of the sintered body. In addition, the thermal conductivity, strength, and Weibull coefficient of the sintered body are summarized in Table 1, which was measured by the laser flash method.

In No. 1, since the linear shrinkage rate was less than 0.2%/hour, large residual pores were generated at the same time as grain growth progressed at low temperatures, so a dense sintered body could not be obtained and the strength was low.

-2 to 6, if the linear shrinkage rate at 1500°C or higher during firing is constant in the range of 0.2%/hour or more and 8%/hour or less, the heat transfer rate is high and the strength of the sintered body is high. 50kgf/mr
It can be seen that the value is r1'' or more, and the variation thereof is small.

In No. 7.8, when the linear shrinkage rate exceeds 8%/hour, the temperature increase rate increases (as a result, the temperature distribution in the firing furnace increases, which tends to cause variations in quality within the same lot. Although the strength was 50 kgf/mm'' or more, the Weibull coefficient was small at 5 to 6, and the strength varied widely.

Example 2 Average particle size 0.8 μm, oxygen content 0.6%, purity 98%
The main component is AlN powder with an average particle size of 1.04t.
m of Y203 powder and carbon black were added in the amounts shown in Table 2. BoJ vinyl butyral (
A suitable amount of PVB) was added to form a molded body, and the molded body was degreased in nitrogen.

The obtained molded body was filled into an AffN crucible and heated under normal pressure for 1
The temperature is raised at a rate of 500°C/hour up to 500°C.
After the temperature exceeded 1500°C, the temperature was increased to achieve various constant linear shrinkage rates, and firing was performed at 1820°C for 4 hours in a nitrogen stream.

The obtained sintered body was ground into a test piece with a size of 3 x 4 x 40 mm, and a three-point bending test was conducted in accordance with J I SRl 601. Thermal conductivity was also measured using the laser flash method.

Table 2 summarizes the raw material blending ratio, thermal conductivity, strength, grain boundary phase, appearance, etc. of the sintered body. In addition, the rate at which abnormalities in the appearance of the sintered body occur when the sintered body is fired 20 times under the same conditions is also shown.

In descriptions 1 to 19, Y2 is added as a sintering aid to AlN as the main component.
O30.5-IO wt%, or Y2O30.5-10
Along with weight%, carbon or a compound that produces carbon upon firing is added in an amount of 0.01 to 0.1% in terms of carbon, and after molding and degreasing, the linear shrinkage rate at 1500°C or higher during firing is 0.2%/ If the temperature is raised constant over time, the strength of the sintered body will be 165W/m at 50kgf/mrn' or more.
High thermal conductivity of K or higher is achieved. It is also shown that when the grain boundary phase of the AβN sintered body is composed of Y4AJ2209 and Y2O3, the incidence of abnormalities in the appearance of the sintered body surface such as graining and coloring is extremely small. Also,
With this additive combination, the grain boundary phase is Y4AJ2209 and YA
Even in Flood 03, the occurrence rate of appearance abnormalities will be as low as 10% or less.

In No. 20.21, if the amount of Y2O3 added is 0.5% by weight or less, the amount of liquid phase generated during sintering is small, so it is not sufficiently densified and the strength is low. Therefore, the thermal conductivity is low (the grain boundary phase is YAG+YAff03), and the occurrence of abnormal appearance on the surface of the net-like sintered body is high.

For N022 to 26, when the carbon content is 0.1% by weight or more, the strength of the sintered body is high, but carbon remains in the sintered body after sintering, and the sintered body tends to turn black (becomes difficult to conduct heat). The rate of occurrence of appearance abnormalities is also high, and the product value is lost.

In case 27, when Y2O3 exceeds 10% by weight, the amount of liquid phase in the sintered body is too large, and the thermal conductivity decreases on the contrary.
At the same time, yellowing tends to occur in a part of the board. Furthermore, the incidence of appearance abnormalities is also high.

[Effects of the Invention] According to the present invention, an Aj2N substrate with high strength, high thermal conductivity, and good appearance can be easily manufactured using pressureless sintering, which has excellent productivity.

Claims (1)

[Claims] 1. A mixture of AlN as the main component and Y_2O_30.5 to 10% by weight as a sintering aid,
After molding and degreasing, the AlN sintered body is heated in a nitrogen stream at a linear shrinkage rate of 0.2%/hour or more at 1500°C or higher, and then sintered at normal pressure at 1750 to 1950°C. manufacturing method. 2. The method for producing an AlN sintered body according to claim 1, wherein carbon or a compound that generates carbon upon firing is further added as a sintering aid in an amount of 0.01 to less than 0.1% by weight in terms of carbon.