JPS6221764A - Manufacture of aluminum nitride - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Emperor 1 Yu Makuji λ! The present invention relates to a method for manufacturing an aluminum nitride sintered body,
More specifically, the present invention relates to a method for producing an aluminum nitride sintered body that is dense and has excellent practical properties such as thermal conductivity, insulation, and dielectric constant.

Conventional technology Semiconductor devices and devices and equipment that utilize them constitute complex thermal systems due to heat generation in semiconductor elements, resistors, coils, etc. Such heat is transmitted through various heat conduction methods, e.g. It will be released outside the device by heat conduction, heat radiation, convection, etc.

In general, semiconductor devices have a maximum permissible temperature (maximum allowable temperature) from the standpoint of characteristics and reliability, and also a permissible range of temperature differences within the device or between devices from the standpoint of noise margin. do.

Therefore, it is extremely important to operate these elements stably and reliably (and to perform the best thermal design) in the design and manufacture of semiconductor devices and the like.

Furthermore, in recent years, there has been a trend toward faster speeds, higher densities, and larger sizes of semiconductor devices, and with this, an increase in the amount of heat generated by semiconductor devices has become a major problem. Therefore, there is a demand for improved heat dissipation of substrates for semiconductor devices, that is, further improvement of thermal conductivity in the thickness direction of the entire substrate. Therefore, substrates for semiconductor devices are required to have high electrical insulation and high heat dissipation properties at the same time.

As a result, the alumina sintered bodies conventionally used as IC substrates have low thermal conductivity and insufficient heat dissipation, so they are susceptible to increased heat generation due to the high integration of IC chips, etc. It is becoming increasingly difficult to respond adequately. Therefore, as an alternative to this alumina substrate, a highly thermally conductive bare IJA substrate is being considered, but beryllia is not only highly toxic and difficult to handle, but also has a limited supply and is expensive, making it impractical. Not.

On the other hand, aluminum nitride (AIN) is attracting attention as an insulating material and a packaging material in the semiconductor industry because it inherently has high thermal conductivity and high insulating properties, and is also low in toxicity.

However, when producing a sintered body from AIN powder, the sinterability of the AIN powder itself is not good, so the relative density (AI
The theoretical density of N (based on 3.26 g/cut) is only about 70 to 80% at most, depending on the sintering conditions, and has a large amount of pores. By the way, the heat conduction mechanism of insulating ceramics such as aluminum nitride sintered bodies consists of ionic and covalent bonds, and is mainly based on phonon conduction due to anharmonic interaction between lattice vibrations. When there are defects such as pores and impurities, phonon scattering is significant and only a material with low thermal conductivity can be obtained.

Therefore, in order to obtain an AIN sintered body that is dense and has good thermal conductivity, various sintering aids are added to the AIN powder.
Attempts have been made to use hot pressing or pressureless sintering, and it has become possible to obtain AIN sintered bodies of fairly good quality. For example, calcium oxide (CaO),
Barium oxide (Ban), strontium oxide (Sr)
Japanese Patent Publication No. 58-49510 discloses a method in which 0.1 to 10% by weight of AIN powder is added to AIN powder and sintered. According to this method, the relative density 9
8% or more, thermal conductivity 0.1-0.13cal 7cm
, sec, deg (42 to 54 W/m4) (room temperature). However, this level of value cannot be said to be sufficient to cope with the large amount of heat generated due to future increases in the degree of integration of IC5LSIs and the like.

In addition, as a hot press method, Can, Ban, SrO
There is a method in which 0.01 to 1% by weight of AIN powder is added to the AIN powder and sintered (see the invention in JP-A-59-50077). However, even with this method, only a thermal conductivity of about 60 to 70 W/m4 can be obtained. Moreover, with this hot pressing method, there are limitations on the shape of the sintered body that can be obtained, and furthermore, this process is an expensive process, so the above-mentioned IC.

It is economically disadvantageous to use it as a substrate for LSI or the like.

- Problems that the original article aims to solve As mentioned above, with the increasing integration of semiconductor devices,
As C-chips and other devices become larger, the amount of heat generated by these elements and devices is expected to increase significantly, but conventional substrates are no longer able to adequately cope with this increase in amount of heat generated. , the development of new substrate materials is desired. Under these circumstances, AIN, which is attracting attention as a high-temperature structural material with high heat resistance, is expected to be used as an insulating material and packaging material in the semiconductor industry due to its excellent thermal conductivity and electrical insulation properties. However, the actual situation is as described above, and a ΔIN sintered body with excellent physical properties that can withstand practical use has not yet been obtained.

Therefore, the purpose of the present invention is to provide an economically advantageous method for manufacturing an AI sintered body with good thermal conductivity, and of course has a high thermal conductivity of 100 W/m4 or more and is dense. It is also an object of the present invention to provide a novel AIN sintered body of high quality.

Means for Solving the Problems In view of the above-mentioned conventional state of the art for manufacturing AIN sintered bodies, the inventors have developed an AIN sintered body having a high thermal conductivity of 100 W/m or more. In order to develop a method by which the body can be obtained by an economically advantageous pressureless sintering method,
As a result of a detailed study of raw material powder purity, sintering aids, sintering conditions, etc., we decided to use AIN powder with a low oxygen content, and use yttrium (Y) and/or cerium (Ce) alkoxide as the sintering additive. The present invention was completed based on the discovery that adding a small amount of is extremely advantageous for achieving the above objective.

That is, in the method for producing an AIN sintered body of the present invention, at least one solution selected from the group consisting of NY and Ce alkoxides is added to AIN powder having an oxygen content of 1.8% by weight or less. Add 0.1 to 10% by weight in terms of Ce, mix and decompose, then mold, then 1700 to 22
It is characterized by being sintered under normal pressure in a non-oxidizing atmosphere at a temperature of 00°C inside an egg.

In the method of the present invention, the non-oxidizing atmosphere means a vacuum or an atmosphere composed of at least one selected from the group consisting of nitrogen gas, hydrogen gas, -carbon oxide gas, argon gas, helium gas, etc. .

Further, in the alkoxide of Y or Ce that can be advantageously used in the method of the present invention, the alkoxide preferably has an alkyl group having 1 to 4 carbon atoms. Such metal alkoxides generally have a low boiling point (100 to 200°C), and therefore can be purified to high purity at low temperatures by vacuum distillation or the like.

In the method of the present invention, an AIN sintered body is manufactured by following a series of steps of blending each component, molding, and firing in the same way as commonly found ceramics. Since it is used as a chemical, it includes a step of hydrolysis after preparation.

To further explain the method of the present invention, first, AIN and a predetermined amount of metal alkoxide or a mixture thereof are mixed, and the alkoxide is hydrolyzed. At this time, the metal alkoxide decomposes into fine powder, which is highly pure and highly active. Next, it is molded into a predetermined shape and sintered under normal pressure. There are no particular restrictions on the molding method, and the most suitable method may be selected from conventionally known methods such as mold molding, rubber press, extrusion molding, injection molding, and casting molding, depending on the shape and dimensions of the desired product. Select and implement.

In addition, it is possible to obtain a target product with a complex shape by combining such a forming method and machining of the dough, and this machining method can produce a uniform product while also improving the dimensional accuracy and surface defects of the final product. Considering the occurrence of such problems, it is necessary to use high-precision technology, and it is desirable to use NC grinding, laser processing, etc.

The dense nature of AIN, which is generally considered to have poor sinterability,
In order to obtain a sintered body with high thermal conductivity, a particular problem was the large amount of pores remaining in the final product. Therefore, by eliminating this porosity, AIN with high thermal conductivity
Methods using various sintering aids have been proposed to produce sintered products, but the ones that have been used in the past are still insufficient, and are suitable for semiconductor devices that are becoming larger and more integrated. A substrate that ensures sufficient heat dissipation is not yet known.

By the way, according to the present invention, Y and/or are used as sintering aids.
Alternatively, by using a Ce alkoxide solution, mixing it with AIN powder, and then hydrolyzing it, a finely powdered high-purity oxide can be obtained, which makes it possible to advantageously obtain a dense and highly thermally conductive AIN sintered body. Ta. In this hydrolysis, the metal alkoxide is added to the AIN powder as a solution in a solvent such as e.g. Hydrolysis is carried out in the presence of water, generally by heating to 0° C. or higher, and the desired fine particulate metal oxide can be obtained.

In the method of the present invention, the target thermal conductivity is particularly 10.
Several conditions act critically when obtaining an AIN sintered body with high heat dissipation of 0 W/+n4 or more. First, AIN
The oxygen content in the powder must be below 1.8% by weight. This is because if oxygen is present in excess of this upper limit, the sintering process will cause oxygen to become ^1203 or Al0
If N is mixed into the AIN sintered body in the form of N, it will cause phonon scattering as mentioned above, resulting in a product with low thermal conductivity, and the desired high thermal conductivity of 100 W/m or more will be obtained. This is because it is not possible to obtain an AIN sintered body with a high yield.

Next, the amount of the metal alkoxide that decomposes to become a sintering aid needs to be in the range of 0.1 to 10% by weight in terms of Y and/or Ce. That is, if it is used in an amount less than the lower limit of 0.1% by weight, a sufficiently dense pressureless sintered body cannot be obtained, and conversely, if it is used in an amount exceeding the upper limit of 10% by weight. In this case, the thermal conductivity of the obtained sintered body decreases, and the desired AIN sintered body with good heat dissipation properties cannot be obtained.

As already mentioned, the alkoxide of Y and the alkoxide of Ce can be added individually or as a mixture, and both can be expected to have the same effect, and in the case of combined addition, the properties of the respective effects are simply added. is known to show.

Moreover, it is preferable that the sintering temperature be within the range of 1700 to 2200°C. This is because sintering does not proceed sufficiently at temperatures below 1,700°C, making it impossible to obtain a dense product with a relative density of 95% or more, and when sintering at temperatures exceeding 2,200°C, AIN decomposes. The reaction is significantly accelerated,
This is because the weight reduction of the sintered body becomes large.

As described above, according to the method of the present invention, a dense AIN sintered body can be obtained by using metal alkoxides as AIN sintering aids and hydrolyzing them after addition. In addition, in order to obtain an AIN sintered body that provides high heat dissipation and is useful as a package substrate for highly integrated semiconductor devices that generate a large amount of heat, the amount of metal alkoxide added, the oxygen content in AlN, the sintering It is necessary to keep the temperature and other conditions within the above ranges, and this allows the pressureless sintering method, which is the most economical sintering method, to have high thermal conductivity (100 W/m4 or more) and high density (more than 100 W/m4). Advantageously, an AIN sintered body with a high relative density is provided.

Although the mechanism by which Y alkoxide, Ce alkoxide, or a mixture thereof promotes sintering of AIN is not clear, finely and uniformly dispersed Y or Ce compounds react with AIN to form a glass-like liquid phase. However, it is thought that as a result, densification and thermal conductivity are improved by liquid phase sintering.

EXAMPLES Below, the present invention will be explained with reference to Examples, but these Examples are not intended to limit the scope of the present invention.

Example 1 A solution of yttrium methoxide, cerium methoxide, or a mixture thereof (solvent: methanol) was added to various aluminum nitride powders with an oxygen content in the range of 0.5 to 1.8% in terms of Y or Ce. Mix 0.6% by weight with 60
After heating to 0° C. to decompose, the mixture was sufficiently mixed in a mortar to prepare a mixed powder.

This was molded under a pressure of 2 tons/cnf, and normal pressure sintered at 1900° C. for 3 hours in a 1 atm N gas atmosphere.

The relative density and thermal conductivity of each obtained sintered body sample were measured, and the results are shown in Table 1 below.

Comparative Example 1 Using aluminum nitride powder with an oxygen content exceeding 1.8% by weight, yttrium methoxide and cerium methoxide were added and mixed in the same manner as in Example 1, followed by decomposition, molding,
A comparative sample was prepared by sintering.

Relative density and thermal conductivity were similarly measured and the results are shown in Table 1. Incidentally, since yttrium methoxide and cerium methoxide have almost the same effect, Table 1 shows the results for only yttrium.

From this result, yttrium has almost the same effect as cerium, and the thermal conductivity is LOQ W/m4
In order to achieve the above, the 0 content of AIN is approximately 1.8% by weight.
It is understood that the smaller this value is, the higher the effect of improving thermal conductivity is.

Furthermore, it can be easily seen that the sintered body obtained by the method of the present invention has an extremely high relative density (99% or more), and the porosity is greatly improved.

Example 2 A solution of yttrium methoxide, cerium methoxide or a mixture thereof (solvent dixylene) was added to aluminum nitride powder with an oxygen content of 1.6% (1.1 to 10% by weight in terms of Y or Ce). The aluminum nitride sintered body of the present invention was produced by adding and mixing various amounts in the range of , decomposing at 550°C, and then molding and sintering in the same manner as in Example 1. The relative density and thermal conductivity of the sintered bodies were as shown in Table 2 below.

Comparative Example 2 Yttrium methoxide and cerium methoxide were added and mixed in an amount outside the range of the present invention to aluminum nitride powder with an oxygen content of 1.6%, and then treated in the same manner as in Example 1 to obtain a comparative sample. Created. Table 2 shows the measurement results of relative density and thermal conductivity.

The results in Table 2 show that by using at least one of Y alkoxide and Ce alkoxide in an amount of 0.1 to 10% by weight, an aluminum nitride sintered body with a high thermal conductivity of 100 W/m4 or more can be advantageously obtained. It shows that it is possible.

Example 3 Yttrium methoxide and cerium methoxide were mixed with Y and C into aluminum nitride powder with an oxygen content of 166%.
Added 0.4% by weight and 0.2% by weight respectively in terms of e,
A sintered body sample was obtained in the same manner as in Example 1. In addition, sintering was performed at a temperature within the range of 1.700 to 2.200°C for 3 hours.
It was carried out according to the pressureless sintering method in a N2 gas atmosphere at atmospheric pressure. Table 3 shows the measurement results of the properties of the obtained sintered body.

Comparative Example 3 Yttrium methoxide and cerium methoxide were added to aluminum nitride powder with an oxygen content of 1.6% in Y and C
After adding and mixing 0.4% by weight and 0.2% by weight of each in terms of e, they were decomposed and molded in the same manner as in Example 1, and then sintered at a sintering temperature outside the range of the present invention to obtain a comparative sample. Obtained. Table 3 shows the measurement results of physical properties.

Example 3 and Comparative Example 3 were carried out to demonstrate that the sintering temperature is a critical condition in order to obtain a sintered body with predetermined characteristics in the method of the present invention. The results in the table clearly show that sufficient thermal conductivity and relative density cannot be ensured when the temperature is below the lower limit of 1700°C.

Example 4 One of yttrium ethoxide, cerium ethoxide, yttrium propoxide, cerium propoxide, yttrium butoxide, and cerium butoxide was added to aluminum nitride powder with an oxygen content of 1.6% as Y or Ce. The aluminum nitride sintered body of the present invention was obtained by adding 5% by weight in terms of conversion and mixing, decomposition, molding, and sintering according to Example 1.

Table 4 shows the measurement results of physical properties.

Example 4 was conducted to confirm the conditions for the length of the anoyl chain in the alkoxide additive,
As is clear from the results in Table 4, there is a tendency for thermal conductivity to decrease as the number of carbon atoms increases;
It has been found that metal alkoxides having alkoxide groups up to 10% give products with sufficient properties as contemplated by the present invention.

Effects of the Invention As explained in detail above, according to the method of the present invention, aluminum nitride powder with an oxygen content of 0.5 to 1.8%,
A solution of at least one of yttrium alkoxide and cerium alkoxide is 0.1 to 1O in terms of Y or Ce.
After mixing by weight% and waiting for hydrolysis, molding, and then 1.
By sintering under normal pressure in a non-oxidizing atmosphere at a temperature of 2.200° C., it is useful as a heat dissipation material or package material for semiconductor devices, which has excellent thermal conductivity in a dense chamber.

The aluminum nitride sintered body obtained by the method of the present invention can be used not only for IC substrates such as circuit boards, server boards, and hybrid IC boards, but also as heat sinks for power transistors, power diodes, and laser diodes. It can be suitably used as an oscillator component or as an insulating thin plate to replace mica, and is expected to have excellent practical effects.

Claims (4)

[Claims] (1) At least one solution selected from the group consisting of yttrium alkoxide and cerium alkoxide is added to aluminum nitride powder having an oxygen content of 1.8% by weight or less in an amount of 0.1 to 10% by weight in terms of yttrium or cerium. , a method for producing an aluminum nitride sintered body, which comprises mixing and decomposing these materials, molding them, and then sintering them under normal pressure in a non-oxidizing atmosphere at a temperature within the range of 1700 to 2200°C. (2) The method for producing an aluminum nitride sintered body according to claim 1, wherein the decomposition is performed by heating to a temperature within a range of 100 to 1,200°C. (3) The method according to claim 2, wherein the solvent in the alkoxide solution is benzene, xylene, toluene, methanol, ethanol, or propanol. (4) The method according to any one of claims 1 to 3, wherein the alkoxide has an alkyl group having 1 to 4 carbon atoms.