JPS6337065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum nitride sintered body suitable for use as a substrate for integrated circuits, etc. The present invention relates to an aluminum nitride sintered body having high thermal conductivity, electrical resistivity, and a low coefficient of thermal expansion, a method for producing the same, and a method for producing the sintered body. Powder composition. In large-scale integrated circuits, circuit components such as semiconductor chips are being mounted in an increasingly dense manner, and the capacity is becoming larger and smaller. Along with this, there is an increasing demand for materials with good heat dissipation properties for the insulating substrates used. Conventionally, alumina sintered bodies have been frequently used for insulating substrates, but their heat dissipation properties are not very good, which is why there is a desire to develop materials for insulating substrates that have higher heat dissipation properties. In addition to thermal conductivity, the properties required for materials for insulating substrates include high electrical insulation, a coefficient of thermal expansion close to that of silicon, high mechanical strength, and low dielectric constant. Examples include. Taking these conditions into consideration, the present inventors focused on aluminum nitride sintered bodies. In other words, the thermal expansion coefficient of the aluminum nitride sintered body is that of the alumina sintered body (approximately 7×10 ^-6 /°C).
The value of silicon single crystal is smaller (approximately 3.3×10 ^-6 /
It has a value of approximately 5×10 ^-6 /°C, close to In addition, regarding mechanical strength, bending strength is approximately 50Kg/mm ²
The above is that of the alumina sintered body (approximately 20 kg/
mm ² ) and has superior electrical insulation properties. A dense sintered body exhibiting such properties can be produced by pressureless sintering or hot pressing. Conventionally, as methods for manufacturing aluminum nitride sintered bodies, (1) reaction sintering method, (2) pressureless sintering method, and (3) hot press sintering method are known. Among these methods, the reactive sintering method is a method in which a metal aluminum compact is sintered while undergoing a nitriding reaction in a nitrogen gas atmosphere. In this method, the nitriding reaction is rate-determined by the diffusion of nitrogen gas, so when the product becomes thick, unreacted metal remains in the center, and the product is porous, so it has not been put to practical use as an electrical insulating material. . In the pressureless sintering method, yttrium oxide and rare earth oxide, yttrium oxide and powders such as silicon dioxide, nickel, and calcium oxide are added to aluminum nitride powder, mixed, and then fired as a compact.
Furthermore, in the hot press method, powders such as aluminum oxide, yttrium oxide, and silicon dioxide are added to aluminum nitride powder, mixed, and then formed into a compact, which is then heated and sintered under pressure. Now, according to the pressureless sintering method or the hot pressing method, a dense sintered body having the above-mentioned physical properties can be obtained. However, the thermal conductivity of the sintered body is usually 0.07 cal/cm・s・℃ (room temperature),
The value is only about 0.1 cal/cm·s·°C at most, and further improvement is required as a material for insulating substrates for integrated circuits. The present invention is based on the above-mentioned viewpoint, and an object of the present invention is to provide a material having characteristics suitable for use as an insulating substrate for large-scale integrated circuits and the like. Its characteristics are that it is a sintered body mainly composed of aluminum nitride, which has a density (relative density) value of at least 90% of the theoretical density of aluminum nitride, and that it contains lithium or a lithium-containing substance. In particular, by containing 0.05 to 5% by weight of lithium, its thermal conductivity is significantly enhanced. Such a sintered body has a thermal conductivity of 0.2 cal/cm・
s・℃ or more, and volume resistivity of 10 ¹² Ω・cm or more,
Average coefficient of thermal expansion in the range from room temperature to 300℃ 5
It exhibits well-balanced characteristics of less than ×10 ^-6 /°C. The sintered body of the present invention is made of a mixture of aluminum nitride as a main component and lithium or a lithium compound added thereto, and the molded body is molded in a non-oxidizing atmosphere at a temperature of 1,600 to 2,000°C to reduce the density of aluminum nitride. can be produced by sintering for a sufficient time to exceed 90% of its theoretical density. It is preferable that the amount of lithium in the lithium or lithium-containing material is 0.05 to 5% by weight. In the present invention, aluminum nitride has an average particle size of
It is used as a powder of 20 μm or less, more preferably 10 μm or less. The lithium content is preferably 0.05% by weight or more to obtain a dense sintered body, and preferably 5% by weight or less to prevent volatilization of the lithium compound during sintering and obtain a dense sintered body. Examples of lithium compounds include lithium oxide,
Lithium halides, lithium nitrate, lithium carbonate, lithium sulfate, etc. are used and can be mixed with the aluminum nitride powder in powder or solution form. Known equipment and methods such as a ball mill can be used for mixing, and the resulting homogeneous mixture is pressure-molded into a desired shape at room temperature. The conditions for firing the aluminum nitride powder compact to which the lithium-containing compound has been added are also important. Firing must be performed in a non-oxidizing (atmospheric or reduced pressure) atmosphere. In an oxidizing atmosphere, aluminum nitride is oxidized, making it impossible to obtain the desired sintered body. The temperature during firing is preferably 1,600 to 2,000°C, and particularly effective is 1,700 to 1,900°C. temperature is 1600
If the temperature is lower than ℃, a dense sintered body cannot be obtained;
If the temperature is higher than 2000℃, over-firing will occur. Further, the firing method may be an atmospheric pressure sintering method or a hot pressing method. If a sintered body is manufactured using the uniaxial hot press method,
Shrinkage occurs only in the axial direction of pressure, resulting in high dimensional accuracy.
A sintered body having higher strength than a sintered body produced by pressureless sintering can be obtained. When sintering by hot pressing, a desired sintered body can be obtained by applying a load of 100 kg/cm ² or more. Regarding the firing time, the optimum value is determined by the particle size of the raw material powder, the amount of lithium-containing compound added, the temperature, and the presence or absence and size of a load applied during firing. In general, the particle size of the raw material powder is small, the temperature is high, and when a load is applied during firing, the greater the load, the more dense the sintered body can be obtained in a shorter time. The present invention resides in a powder composition for producing the above-mentioned sintered body, the aluminum nitride powder composition for producing the sintered body comprising a powder containing aluminum nitride as a main component and containing lithium or a lithium-containing substance. It's in things. By using the powder composition of the present invention, a dense sintered body with high thermal conductivity can be obtained. Next, examples will be shown and specifically explained. Example 1 Lithium carbonate with an average particle size of 5 μm was added to aluminum nitride powder with an average particle size of 2 μm in terms of lithium.
It was added and mixed at a concentration of 0.03 to 10% by weight. Next, a pressure of 1000 Kg/cm ² was applied to the mixed powder at room temperature to form a compact. The compact was then sintered in a firing furnace at a reduced pressure of 1×10 ⁻³ to 1×10 ⁻⁵ torr.
The furnace heats up from room temperature to 1800℃ in about 1 hour.
After holding at ℃ for 0.5 hour, it was allowed to cool. Table 1 shows the characteristics of the sintered body produced as described above. When the lithium carbonate added to the aluminum nitride powder is 0.05 to 5% by weight as lithium, 0.2 cal/cm・
It has a thermal conductivity of s・℃ or more, a volume resistivity of 10 ¹² Ωcm or more, and a thermal expansion coefficient of 5×10 ^-6 /℃ or less, and a density (relative density) of 90% or more of the theoretical density of aluminum nitride. A sintered body has been obtained that is densified by the time it becomes . Example 2 In the same manner as described in Example 1, 1% by weight of lithium carbonate was added as lithium to aluminum nitride powder to obtain a molded body from the mixed powder,
Sintered bodies were manufactured in vacuum by changing the firing conditions. Table 2 is a table showing the relationship between the manufacturing conditions of the sintered body and the relative density of the obtained sintered body. All sintered bodies densified to a relative density of 90% or more have a density of 0.2 cal/cm・
It had a thermal conductivity (room temperature) of s·°C or higher, a volume resistivity (room temperature) of 10 ¹² Ωcm or higher, and a thermal expansion coefficient (room temperature to 300°C) of 4.2 to 4.3×10 ⁻⁶ /°C.

【table】

【table】

[Table] Example 3 In the same manner as described in Example 1, lithium carbonate was added to aluminum nitride powder as lithium.
After obtaining a molded body from the mixed powder added in a weight percent, the molded body was fired to obtain a sintered body. However, in this example, the atmosphere during the production of the sintered body was argon gas,
Helium gas, nitrogen gas, or hydrogen gas was used. In each case, the obtained sintered body was the same as that of Example 1.
It had the same characteristics as the sintered body described in 2.1 with a lithium content of 1% by weight. Example 4 In the same manner as in Example 1, lithium oxide, lithium nitride, lithium hydride, lithium hydroxide, lithium halide, lithium nitrate, or lithium sulfate was added in an amount of 0.03 to 10% by weight as lithium to aluminum nitride. A sintered body was obtained. The obtained sintered body had almost the same characteristics as the sintered body described in Example 1 with the same amount of lithium added, even when any of the above-mentioned lithium compounds was used. Example 5 A sintered body was obtained in the same manner as in Example 1 by adding and mixing 1% by weight of lithium carbonate as lithium to aluminum nitride powders having different average particle sizes. Table 3 shows the relative density of the obtained sintered body, and if the average grain size of aluminum nitride is 20 μm or less, the relative density is
A sintered body with 90% or more densification was obtained. A sintered body with a relative density of 90% or more is
Thermal conductivity of 0.2 cal/cm・s・℃ or higher (room temperature), 10 ¹²
Volume resistivity of Ωcm or more (room temperature), 4.2 to 4.3×10 ^-6 /
It had a coefficient of thermal expansion of 300°C (room temperature to 300°C).

[Table] Example 6 As a specific application example of the electrically insulating substrate of the present invention, a semiconductor power module using the aluminum nitride sintered body containing 1% by weight of lithium obtained in Example 1 as an insulating substrate will be explained. do. FIG. 1 is an assembled sectional view of a conventional structure. conductor 4
and the heat sink 6 and between the heat sink 6 and the metal support plate 8 with the organic insulator 5 and the alumina substrate 7, respectively, and in order to alleviate the strain caused by the difference in thermal expansion coefficient between the silicon element 1 and the heat sink 6. A molybdenum spacer 3 is interposed therebetween. FIG. 2 is an assembled sectional view of a module using an insulating substrate according to the present invention. The insulating substrate 10 is directly brazed to the silicon element 1, and has an extremely simple structure. The above semiconductor device was subjected to a heat cycle in which the temperature was held at -60°C for 30 minutes, then at room temperature for 5 minutes, and then the temperature was raised to 125°C and held for 30 minutes. In the semiconductor device using the conventional method (Figure 1), peeling occurred at the soldered points after 20 heat cycles. No abnormality was observed in the semiconductor device of the present invention (FIG. 2) even after 150 heat cycles. Comparative Example Yttrium oxide was added in an amount of 10% by weight to aluminum nitride powder having an average particle size of 2 μm, and the mixture was mixed to form a compact. The molded body was hot pressed in a vacuum of 1×10 ⁻⁴ torr at a temperature of 1800° C. and a load of 300 kg/cm ² for 0.5 h to obtain a sintered body. The sintered body has a relative density of 99%
It was elaborated to. Other properties of the sintered body include thermal conductivity of 0.07 cal/cm・s・℃ (room temperature), electrical resistivity of 10 ¹¹ Ω・cm (room temperature)), and thermal expansion coefficient of 5×.
10 ^-6 /°C (room temperature to 300°C). As is clear from the above examples, the aluminum nitride sintered body of the present invention is dense and has the characteristics of high thermal conductivity, high electrical resistivity, and low coefficient of thermal expansion. Therefore, as mentioned above, it is not only useful as a substrate material for electrical insulation, but also for materials that require heat resistance, oxidation resistance, chemical resistance, thermal shock resistance, and high strength at high temperatures. This material is also suitable for use as a member.

[Brief explanation of the drawing]

FIG. 1 is an assembled sectional view of a silicon semiconductor device according to a conventional method, and FIG. 2 is an assembled sectional view of a silicon semiconductor device using a substrate according to the present invention. DESCRIPTION OF SYMBOLS 1... Silicon element, 2... Lead wire, 3... Molybdenum spacer, 4... Conductor, 5... Organic insulator, 6
...Heat sink, 7. Alumina substrate, 8. Support plate, 9. Solder, 10. Aluminum nitride sintered body substrate.

Claims (1)

[Claims] 1 The main component is aluminum nitride, which contains lithium or a lithium-containing substance, and has a theoretical density of 90%.
An aluminum nitride sintered body characterized by having a density of % or more. 2. Claim 1, wherein the amount of lithium in the lithium or lithium-containing material is 0.05 to 5% by weight.
The aluminum nitride sintered body described in . 3 Thermal conductivity at room temperature is 0.2 cal/cm・s・℃
The aluminum nitride sintered body according to claim 1, which is the above. 4. The aluminum nitride sintered body according to claim 1, which has a volume resistivity of 10 ¹² Ωcm or more at room temperature. 5 Claim 1 in which the average coefficient of thermal expansion is 5×10 ^-6 /°C or less in the range from room temperature to 300°C
The aluminum nitride sintered body described in . 6. The aluminum nitride sintered body according to claim 1, on which a semiconductor element is mounted. 7 A powder containing aluminum nitride as a main component and lithium or a lithium-containing substance is formed into a compact, and the compact is heated in a non-oxidizing atmosphere at a temperature sufficient to cause the density to exceed 90% of the theoretical density. A method for producing an aluminum nitride sintered body, which is characterized by sintering. 8. The method for producing an aluminum nitride sintered body according to claim 7, wherein the aluminum nitride sintered body is sintered by hot pressing at a temperature of 1600 to 2000°C and a pressure of 100 kg/cm ² or more. 9. A method for producing an aluminum nitride sintered body according to claim 7 or 8, which uses aluminum nitride powder having an average particle size of 20 μm or less. 10. An aluminum nitride powder composition for producing a sintered body, comprising a powder containing aluminum nitride as a main component and lithium or a lithium-containing substance therein.