JPS6236069A - Manufacture of aluminum nitride sintered body - 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] Industrial Application Field The present invention relates to a method for producing 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 and insulation (permittivity).

Conventional technology Semiconductor devices, devices and equipment using these 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 from the standpoint of noise margin, there is a tolerance range for temperature differences within the device or between devices. exist.

Therefore, in order to operate these elements stably and reliably, it is extremely important 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, a highly thermally conductive beryllia substrate is being considered as an alternative to this alumina substrate, but beryllia is not only highly toxic and difficult to handle, but also is not practical because it is scarce and expensive.

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

However, when producing the sintered body from AIN powder, the relative density of the AIN sintered body obtained by sintering after powder compaction (Af
(based on the theoretical density of fiN 3.26 g/cj) is
Although it depends on the sintering conditions, it is only about 70-80% at most.
Moreover, it has a large number 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 AzNfi compacts that are dense and have good thermal conductivity, attempts have been made to add various sintering aids to AJN powder and perform hot pressing or pressureless sintering. It has become possible to obtain A1N sintered bodies.

For example, calcium oxide (Cab), barium oxide (B
ad), a method in which strontium oxide (SrO) or the like is added to AIN powder in a proportion of 0.1 to 10% by weight and sintered is disclosed in Japanese Patent Publication No. 58-49510. According to this method, the relative density is 98% or more, the thermal conductivity is 0.1 to 0.13 cal/c+m, sec, deg.
(42 to 54 W/m, k) (room temperature) product has been obtained. However, with this level of value, future IC,
It cannot be said that it can sufficiently cope with the large amount of heat generated due to the increase in the degree of integration of LSIs and the like.

In addition, as a hot press method, CaO, BaO, SrO
There is a method of adding 0.01 to 1.0% by weight of AIN powder to AIN powder and sintering it. (Unexamined Japanese Patent Publication No. 59-50077
However, even with this method, only a thermal conductivity of about 60 to 70 W/kg can be obtained.Furthermore, with this hot pressing method, the shape of the obtained sintered body is Due to the limitations and furthermore, this process is an expensive process, the above-mentioned IC.

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

Problems to be Solved by the Invention As mentioned above, as semiconductor devices become more highly integrated, I
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, AfN, which is attracting attention as a high-temperature structural material with high heat resistance, has thermal conductivity, electrical insulation,
Because it is excellent in both, it is expected to be used as an insulating material and a packaging material in the semiconductor industry, but the actual situation is as described above, and so far, AIN sintered bodies with excellent physical properties that can withstand practical use are not available. It has not been done.

Therefore, an object of the present invention is to provide an economically advantageous method for manufacturing an AIN sintered body with good thermal conductivity.
Of course, it is also an object of the present invention to provide a novel dense AJN sintered body that has a high thermal conductivity of 100 W/in or more.

Means for Solving the Problems The present inventors have developed an AIN sintered body having a high thermal conductivity of 100 W/m or more, in view of the above-mentioned conventional state of the manufacturing method for AIN sintered bodies. In order to develop a method that can obtain Aj! by an economically advantageous pressureless sintering method, we conducted detailed studies on raw material powder purity, sintering aids, sintering conditions, etc., and found that Aj! The present invention was completed based on the discovery that using N powder and adding small amounts of calcium oxide (Cab) and calcium fluoride (CaFz) as sintering additives is extremely advantageous for achieving the above object.

That is, Aj! of the present invention! The manufacturing method of N sintered body is 0.5~
AIN powder with an oxygen content rate of 1.5% by weight,
．． 01-0.07% by weight of calcium oxide and 0.1
~0.7% by weight of calcium fluoride is added, mixed, molded, and then pressureless sintered in a non-oxidizing atmosphere at a temperature within the range of 1700 to 2200°C. It is something.

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. .

In the method of the present invention, the AAN sintered body is manufactured in the same way as commonly used ceramics by following a series of steps of preparing each component, molding, and firing.

To further explain the method of the present invention, first, AIN and predetermined amounts of calcium oxide and calcium fluoride are mixed. Next, it is molded into a predetermined shape and sintered under normal pressure. There are no particular restrictions on the molding method, and conventional methods such as mold molding, rubber press,
Select and implement the most suitable method from extrusion molding, injection molding, casting molding, etc.

In addition, it is also possible to obtain a target product with a complex shape by combining this molding method with machining of the dough, and this machining method can achieve uniformity while reducing the dimensional accuracy of the final product and the occurrence of surface defects. Considering these factors, it is necessary to use high-precision technology, and it is desirable to use NC grinding, laser processing, etc.

Effect-a is the dense nature of A6N, which is said 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 reducing the amount of pores, 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 maintains sufficient heat dissipation is not yet known.

By the way, according to the present invention, it has become possible to advantageously obtain a dense and highly thermally conductive AIN sintered body by using calcium oxide and calcium fluoride as sintering aids.

In the method of the present invention, a particularly targeted thermal conductivity of 10
When obtaining an AIN sintered body with high heat dissipation of 0 W/m or more, several conditions act critically.

Firstly, the oxygen content in the AIN powder must be between 0.5 and 1.5% by weight, because if oxygen is present above this upper limit, the oxygen power Al5o will be reduced during the sintering process.
z Aluminum is mixed into the Al1N sintered body in the form of Al0N(7), which causes phonon scattering as mentioned above, resulting in a product with low thermal conductivity.
This is because it is impossible to obtain an AIN sintered body with a high thermal conductivity of 00 W/m or more.

Moreover, if it is less than 0.5% by weight, Aj! The sinterability of the N powder is significantly inhibited, making it impossible to obtain a relative density of 95% or more.As a result, the thermal conductivity also drops to 1001, making it impossible to obtain a relative density of 95% or more.

Next, the amounts of calcium oxide and calcium fluoride added as sintering aids were each 0. It is necessary that O is in the range of 1 to 0.07% by weight and 0.1 to 0.7% by weight. That is, if the amount is less than the lower limit of 0.01% by weight or 0.1% by weight, a sufficiently dense pressureless sintered body cannot be obtained; If it is used in an amount exceeding 0.7% by weight, the thermal conductivity of the obtained sintered body will decrease, and the desired heat dissipation property of AfN will decrease.
A sintered body cannot be obtained.

It is known that when calcium oxide and calcium fluoride are added individually, the effect is small, and that a thermal conductivity of 100 W/m or more can only be obtained when they are added as a mixture.

In addition, it is preferable that the sintering temperature be within the range of 1700 to 2200°C, since sintering will not proceed sufficiently at temperatures below 1700°C, making it impossible to obtain a dense product with a relative density of 95% or more. First, if sintering is performed at a temperature exceeding 2200'C, the decomposition reaction of Al1N will be significantly accelerated, resulting in a large weight loss of the sintered body.

As described above, according to the method of the present invention, by using calcium oxide and calcium fluoride as sintering aids for AfN, dense A7! It becomes possible to obtain a N sintered body. In addition, in order to obtain an AIN sintered body that provides high heat dissipation properties and is useful as a packaging substrate for highly integrated semiconductor devices that generate a large amount of heat, it is necessary to rate,
It is necessary to keep the conditions such as sintering temperature within the above ranges, and this allows the atmospheric pressure sintering method, which is the most economical sintering method, to achieve high thermal conductivity (over 100 W/m). An AβN sintered body with high density (high relative density) is advantageously provided.

A mixture of calcium oxide and calcium fluoride is AIN
Although the mechanism promoting sintering of CaO and C is not clear,
It is thought that a glass-like liquid phase is generated by the reaction of aFz and AfN, and densification and granulation of the crystalline Mi texture occur due to liquid phase sintering, thereby improving thermal conductivity.

In addition, as shown in the examples below, the thermal conductivity is Ca
This shows a significant increase compared to the aluminum nitride sintered body to which O and CaFt are not added. This is considered to be because the combination of AβN powder with an optimal oxygen content, CaO, and CaFz sufficiently achieved densification and low defect concentration of the aluminum nitride sintered body. Furthermore, it is thought that the granularity of the crystal structure contributes to the improvement of thermal conductivity.

EXAMPLES Hereinafter, the present invention will be explained by examples, but these examples do not limit the scope of the present invention.

Example 1 A mixture of 0.05% calcium oxide and 0.4% calcium fluoride was added to various aluminum nitride powders with an oxygen content in the range of 0.5 to 1.5% by weight, and milled in a ball mill for 12 hours.
A mixed powder was prepared by mixing for a period of time. 2 tons/cat of this
It was molded under a pressure of 1 atm of N at 1900°C for 3 hours.
Normal pressure sintering was performed in a 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 of more than 1.5% by weight or aluminum nitride powder with an oxygen content of less than 0.5% by weight, and adding calcium oxide and calcium fluoride in the same manner as in Example 1.・Comparative samples were prepared by mixing, molding, and sintering. Relative density and thermal conductivity were similarly measured and the results are shown in Table 1.

This result also shows that the oxygen content of AIN needs to be 0.5 to 1.5% by weight in order to increase the thermal conductivity to 100 W/m or more. 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 has significantly improved porosity.

Example 2 Calcium oxide was added to aluminum nitride powder with an oxygen content of 1.2% by weight in various amounts ranging from 0.01 to 0.07% by weight and calcium fluoride in the range from 0.1 to 0.7% by weight. - The materials were mixed, molded and sintered in the same manner as in Example 1 to produce an aluminum nitride sintered body of the present invention.

The relative density and thermal conductivity of the obtained sintered body are as follows: The results were as shown in Table 2.

Comparative Example 2 A comparative sample was prepared by adding and mixing calcium oxide and calcium fluoride in amounts outside the range of the present invention to aluminum nitride powder containing 1.2% by weight of oxygen-containing N, and then treating the mixture in the same manner as in Example 1. . Table 2 shows the measurement results of relative density and thermal conductivity.

The results in Table 2 show that by using calcium oxide in an amount of 0.01 to 0,607% by weight and calcium fluoride in an amount of 0.1 to 0.7% by weight, a high thermal conductivity of 100 W/m or more can be obtained by nitriding. This shows that aluminum sintered bodies can be advantageously obtained.

Example 3 0.05% by weight of calcium oxide and 0.5% by weight of calcium fluoride were added to aluminum nitride powder with an oxygen content of 1.2% by weight.
A sintered body sample was obtained in the same manner as in Example 1 by adding a mixture of % by weight. Incidentally, the sintering was carried out at a temperature within the range of 1,700 to 2,200° C. for 3 hours in a N2 gas atmosphere of 1 atm according to an atmospheric pressure sintering method. Table 3 shows the measurement results of the properties of the obtained sintered body.

Comparative Example 3 0.05% by weight each of calcium oxide and calcium fluoride in aluminum nitride powder containing 1.2% by weight of oxygen-containing N
and 0.5% by weight were added and mixed, 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. Table 3 shows the measurement results of physical properties.

Example 3 and Comparative Example 3 were conducted 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 clearly show that sufficient thermal conductivity and relative density cannot be secured if the temperature is lower than Shimoken's 1,700°C.

Effects of the Invention As explained in detail above, according to the method of the present invention, 0.01-0.07% by weight of calcium oxide and 0.1 to 1.5% by weight of oxygen-containing aluminum nitride powder are added to 1005 to 1.5% by weight of oxygen-containing aluminum nitride powder. By mixing and adding 0.7% by weight of calcium fluoride, molding, and then sintering under normal pressure at a temperature of 1.700 to 2,200°C in a non-oxidizing atmosphere, ¥1tIf!
It is useful as a heat dissipation material or packaging material for semiconductor devices because it is inexpensive and has particularly excellent thermal conductivity.

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

[Brief explanation of the drawing]

FIG. 1 is an optical micrograph showing a typical example of the crystal structure of an aluminum nitride sintered body obtained by the manufacturing method according to the present invention at a magnification of xzoo.

Claims (1)

[Claims] Aluminum nitride powder with an oxygen content of 0.5 to 1.5% by weight is mixed and molded with 0.01 to 0.07% by weight of calcium oxide and 0.1 to 0.7% by weight of calcium fluoride, A method for producing an aluminum nitride sintered body, which is then sintered under normal pressure in a non-oxidizing atmosphere at a temperature of 1700 to 2200°C to generate a granular crystal structure.