JPH0717453B2 - Aluminum nitride sintered body and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum nitride sintered body having high thermal conductivity and a method for producing the same.

(Prior Art) In recent years, the amount of heat generated by an LSI increases as the degree of integration of semiconductor elements such as an LSI increases, so that it becomes necessary to quickly transfer and dissipate the generated heat to the outside. Further, in a substrate and a package for mounting a high-power semiconductor element such as a power transistor and a laser diode, heat generated during the operation of the element must be released to the outside of the element within a short time.

A substrate material having high thermal conductivity is required to mount such a semiconductor element that generates a large amount of heat. Conventionally, a beryllium oxide (BeO) -based sintered body has been used as a material for an insulating substrate having such high thermal conductivity. Was used, but its range of use was limited because of its toxicity.

Therefore, recently, aluminum nitride (AlN) has been attracting attention as such a high thermal conductive material because of its high thermal conductivity and high mechanical strength, but AlN is inherently flame retardant. That is, since it has a strong covalent bond like SiC and Si ₃ N ₄ and is difficult to sinter by itself, a manufacturing technique of an aluminum nitride sintered body to which a sintering aid such as Y ₂ O ₃ is added has been studied. (For example, JP-A-60-127267, JP-B-47-18655,
Japanese Patent Publication No. 48-18925).

(Problems to be Solved by the Invention) However, the thermal conductivity of the known aluminum nitride-based sintered body, to which Y ₂ O ₃ is simply added, is,
As disclosed in JP-A-60-127267, about 40 W / m ° K, about 80 W / m ° K even in a yttria-added aluminum nitride sintered body using a high-purity aluminum nitride raw material, the aluminum nitride itself Has a theoretical thermal conductivity of 32
It is considerably low compared with 0 W / m ° K. (Means for Solving the Problems) The present invention has been intensively studied in view of the above problems, and in addition to the yttrium compound in the grain boundary phase of aluminum nitride, a carbide or nitride of titanium, zirconium or tantalum, or
It has been found that an aluminum nitride sintered body in which at least one kind of boron carbide coexists is sufficiently densified and has high thermal conductivity.

Therefore, in the present invention, a highly dense aluminum nitride sintered body having a higher thermal conductivity than that of the AlN—Y ₂ O ₃ binary system, that is, a thermal conductivity of at least 60 W / m ° K. Aim to get.

According to the present invention, the yttrium compound and at least one of carbides or nitrides of titanium, zirconium or tantalum and carbides of boron coexist in the grain boundary phase of aluminum nitride. A sintered body is provided. Also, aluminum nitride
85-99.8% by weight and yttrium oxide 0.1-10% by weight
Aluminum nitride characterized by being formed into a mixed powder of 0.1 to 5% by weight of at least one of carbides of boron, titanium, zirconium or tantalum, and then firing at 1600 to 2100 ° C in a non-oxidizing atmosphere. Provided is a method for manufacturing a quality sintered body.

That is, it is considered that heat conduction of aluminum nitride (AlN) is mainly performed by phonons (elastic waves), and carbides of boron (B), titanium (Ti), zirconium (Zr) or tantalum (Ta) are added. It is estimated that the grain boundary phase of the conventional AlN-Y ₂ O ₃ system sintered body is mainly composed of yttria (Y ₂ O ₃ ) compound, and the phonons are largely scattered. In the body, the above carbides or nitrides are mainly present in the grain boundary phase. Unlike the insulator such as AlN, such a carbide or nitride has electronic conductivity, and this heat conduction is mainly performed by electrons instead of phonons.

Therefore, carbides or nitrides such as Y ₂ O ₃ are present in the grain boundary phase.
When coexisting with, it is considered that phonon scattering due to grain boundaries is less likely to occur, resulting in improved thermal conductivity.

If the AlN content is less than 85% by weight, the amount of AlN, which is a high thermal conductivity component, decreases, the thermal conductivity decreases, and the flexural strength deteriorates.
If it exceeds 5% by weight, the amount of sintering aid decreases and the sintering becomes insufficient. If Y ₂ O ₃ is less than 0.1% by weight, the AlN compact containing an effective amount of carbide cannot be sufficiently densified.
On the other hand, if it exceeds 10% by weight, the grain boundary phase mainly composed of Y ₂ O ₃ increases, and the thermal conductivity decreases.

In addition, the above carbide (B ₄ C, TiC, ZnC or TaC) is 0.1% by weight.
If it is less than 5, the effect of controlling phonon scattering is small and 5
On the other hand, if the content exceeds 50% by weight, the amount of change in the grain boundaries becomes too large, and conversely the phonon scattering increases, the thermal conductivity decreases, and the relative density decreases.

If the firing temperature is lower than 1600 ° C, the sintering will be insufficient and the densification of the sintered body will not proceed, and if it is higher than 2100 ° C, sublimation will be severe and decomposition will be likely to occur. Also, the firing atmosphere must be a non-oxidizing atmosphere. In the oxidizing atmosphere, the surface of the aluminum nitride particles is oxidized, the number of oxide grain boundary phases increases, and the number of voids increases, so that it is possible to obtain a good quality aluminum nitride sintered body that is sufficiently densified and has high thermal conductivity. Disappear.

Even in a non-oxidizing atmosphere, in an argon atmosphere or the like, carbides of boron (B), titanium (Ti), zirconium (Zr) or tantalum (Ta) are generated at grain boundaries. However, it is considered that in the N ₂ atmosphere, it is converted into a nitride as shown in the following formula.

B ₄ C + 2N ₂ → 4BN + C 2TiC + N ₂ → 2TiN + 2C 2ZrC + N ₂ → 2ZrN + 2C In this case, carbon (C) serves as free carbon, for example, to remove impurity oxygen in AlN as CO ₂ .
Moreover, it is considered that TaC is unlikely to be converted into a nitride.

For the above reason, when a mixed powder containing a carbide of boron (B), titanium (Ti), zirconium (Zr) or tantalum (Ta) is fired in an N ₂ atmosphere, the above-mentioned in the grain boundary phase of the AlN sintered body Since the above metals exist as nitrides other than carbides, it was considered that they were added as nitrides from the beginning.
However, in this case, as described above, the impurity oxygen in AlN is changed to CO ₂
It is considered that the same result as the addition of the carbide cannot be obtained because there is no C component to be removed as.

The composition of the aluminum nitride sintered body obtained in the present invention is a large number of fine AlN crystals (average grain size: 1.5 to 10 μm), and the grain boundary phase thereof is an yttrium (Y) compound, boron (B), titanium ( Ti), zirconium (Zr) or tantalum (Ta) at least one compound coexists.

In the present invention, in addition to yttria as a sintering aid,
It is essential that a specific amount of carbide is blended,
This carbide does not always have to be positively added from others, and may be contained in the aluminum nitride powder raw material in advance.

As a result, a highly heat conductive aluminum nitride sintered body can be obtained.

Although this theory has not been elucidated yet, according to the present invention, an aluminum nitride sintered body using an aluminum nitride raw material powder having a relatively high purity even if an aluminum nitride raw material powder having a relatively high purity is used, Equivalent high thermal conductivity can be obtained, and the manufacturing cost can be reduced. Of course, if a high-purity material is used, the high thermal conductivity will be further improved.

(Example) Aluminum nitride (Al) having an average particle size of 1.2 μm and a purity of 97.0%
N) powder (oxygen content 1.5% by weight) as a main component, Y ₂ O ₃ powder (3% by weight) with an average particle size of 0.8 μm and B ₄ C, TiC ZrC with an average particle size (3 μm or less) , And TaC were added and mixed in the respective amount ratios (0.5 and 3% by weight) shown in Table 1, and 6% by weight of paraffin wax was further added as a binder.
And 1% by weight of stearic acid were added and mixed, and press-molded at a molding pressure of 1000 kg / cm ² .

Next, after debinding the obtained molded body by a conventional method,
An aluminum nitride sintered body was obtained by heating and firing at 1860 ° C. for 30 minutes in a nitrogen atmosphere (1 atm). Further, 3% by weight of Y ₂ O ₃ powder was simply added to and mixed with the main component of the same aluminum nitride powder as described above (the amount of carbide added was 0% by weight), which was used as a comparative example of the above-described inventive examples.

When the bulk density of these sintered bodies was measured by the Archimedes method and the thermal conductivity thereof was measured by the laser flash method, the results shown in Table 1 were obtained.

Further, each sample described in the above table is illustrated by adding a sample number to FIG.

As can be understood from Table 1 and FIGS. 1 to 4, AIN-
The Y ₂ O ₃ system with a small amount of carbide added only has the AlN-Y ₂ O ₃ system (heat conductivity of 80 W / m ° K) with an improvement in the heat conductivity (heat conductivity of 0.5 Wt% of the amount of carbide added). The effect of 80 W / m ° K or more) is recognized, and the bulk density is 90% or more.

The above-mentioned sintered body was based on the atmospheric pressure method, but a test result with a similar tendency can be obtained by performing the hot pressing method. In that case, since the density of the sintered body is further increased, the thermal conductivity is generally To rise.

The green body may be formed by press molding, tape molding, or cast molding.

(Effects of the Invention) As described above, according to the present invention, a high thermal conductivity aluminum nitride sintered body could not be obtained unless the conventional high-purity aluminum nitride powder raw material and various sintering aids were used. By using a simple sintering aid of Y ₂ O ₃ -carbide in the above-mentioned specific range, a highly heat-conductive aluminum nitride sintered body can be obtained from an aluminum nitride powder raw material having a relatively low purity.

Therefore, the present invention is extremely advantageous as compared with the conventional method.

[Brief description of drawings]

The drawings are plots of Examples and Comparative Examples of the present invention shown in Table 1. FIG. 1 is a B ₄ C-added system, FIG. 2 is a TiC-added system, and FIG. 3 is a ZrC-added system. The figure is a graph showing the thermal conductivity and the bulk density of the TaC-added system.

Claims (2)

[Claims] 1. A yttrium (Y) compound in a grain boundary phase of aluminum nitride (AlN) and a carbide or nitride of titanium (Ti), zirconium (Zr) or tantalum (Ta) and a carbide of boron (B). An aluminum nitride-based sintered body characterized in that at least one kind thereof coexists. 2. Aluminum nitride (AlN) 85-99.8% by weight
And 0.1 to 10% by weight of yttrium oxide (Y ₂ O ₃ ) and 0.1 to 5% by weight of at least one kind of carbide of boron (B), titanium (Ti), zirconium (Zr) or tantalum (Ta). 1600 in a non-oxidizing atmosphere after molding
A method for producing an aluminum nitride-based sintered body, which comprises firing at ~ 2100 ° C.