JPS6236989B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel silicon carbide sintered body with high thermal conductivity. In recent years, the semiconductor industry has made remarkable progress, and circuit components such as semiconductor chips are increasingly mounted on insulating substrates used in large-scale integrated circuits and the like at an increasingly high density. Furthermore, there is a growing demand for larger capacity and smaller size, and the insulating substrate used is now required to be made of a material with good heat dissipation properties.
Conventionally, alumina sintered bodies have been used as the material for such insulating substrates, but alumina substrates do not have very good heat dissipation, so in order to achieve this purpose, it is necessary to develop an insulating substrate with higher heat dissipation. It has started to be requested. As an insulating substrate material, it has (1) high electrical insulation, (2) high thermal conductivity, (3) thermal expansion coefficient close to that of silicon, and (4) high mechanical strength. The following are required. By the way, the thermal expansion coefficient of silicon carbide sintered body is about 4×10 ^-6 /℃, which is about 8× that of alumina.
10 ^-6 /°C, and close to the thermal expansion coefficient of silicon, approximately 3.3×10 ^-6 /°C. It also has a mechanical strength of ^over 50Kg/mm2 in terms of bending strength, which is about 20% higher than that of alumina.
It is known to have extremely high strength compared to Kg/mm ² . Thermal conductivity of silicon carbide sintered body is 0.1~
It has a value of 0.3 cal/cm・sec・℃, which is about three times higher than that of alumina. From these points, if silicon carbide with high electrical insulation properties is developed, it will be extremely useful as a material for insulating substrates such as large-scale integrated circuits. Silicon carbide is a - group compound semiconductor consisting of carbon and silicon. For this reason, it is considered difficult to obtain a high-density sintered body having electrical insulation properties, and in fact, such a body has not been found to date. Because silicon carbide is a compound with strong covalent bonds, it is well known that it is hard and strong, and is a stable substance with excellent oxidation and corrosion resistance even at high temperatures of 1500°C or higher. Therefore, it was a difficult material to sinter at high density. Therefore, various sintering aids have been used to obtain high-density silicon carbide sintered bodies. For example, by adding aluminum or iron and hot pressing, silicon carbide has a theoretical density of 98%.
% [Alliegro et al. J. Am. Ceram. Soc., 39 ,
386-389 (1956)]. In addition, a method is known that uses boron and carbon to obtain a high-density sintered body using a hot press method or a non-pressure method (Japanese Unexamined Patent Application Publication No. 49-118).
No. 99308). All of these are intended to provide heat-resistant structural materials such as gas turbine parts. The thermal conductivity of silicon carbide sintered bodies using these sintering aids is 0.4 cal/cm・
sec・℃ or less. In addition, silicon carbide with Be added and sintered is shown in JP-A-53-67711, JP-A-55-32796, and their corresponding U.S. Pat. No. 4,172,109; 0.5 in silicon carbide powder
The present invention relates to a high-strength material sintered using a material containing up to 5% by weight of excess carbon. I got it. An object of the present invention is to provide a silicon carbide sintered body with high thermal conductivity. In the present invention, beryllium oxide has a beryllium content.
The silicon carbide sintered body is comprised essentially of 0.1 to 3.5% by weight, 0.1% by weight or less of aluminum, 0.1% by weight or less of boron, 0.4% by weight or less of free carbon, and the remainder essentially silicon carbide. By controlling the impurities to be 0.1% by weight or less of aluminum and 0.1% by weight or less of boron, it is possible to further obtain a thermal conductivity of 0.6 cal/cm·sec·°C or more. It is preferable that the density of the sintered body is 90% or more of the theoretical density. The sintered body of the present invention contains silicon carbide as a main component in the fired state, contains 0.1 to 3.5% by weight of beryllium, and has a thermal conductivity of 0.4 cal/cm・sec・
It is obtained by firing a mixed powder of silicon carbide powder containing impurities controlled to a predetermined amount above .degree. C. and beryllium oxide to a high density.
In particular, a hot press method in which pressure firing is performed at a high temperature is preferred. If the amount of beryllium is less than 0.1% by weight, at room temperature
It is not possible to obtain a thermal conductivity of 0.4 cal/cm・sec・℃ or higher. On the other hand, if the amount exceeds 3.5% by weight, the coefficient of thermal expansion of the sintered body becomes greater than 4×10 ⁻⁶ ° C., which poses a problem particularly when used as a support for silicon semiconductor devices. The above beryllium is added as BeO. Addition involves mixing BeO powder into silicon carbide powder. At this time
By adding about 0.5 to 14% by weight of BeO, it can be contained in the sintered body in an amount of 0.1 to 3.5% by weight. However, it varies slightly depending on the atmosphere and temperature during sintering. What is important in the present invention is that the silicon carbide powder does not contain more than 0.4% by weight of free carbon. More than 0.4% by weight of free carbon significantly reduces thermal conductivity. The beryllium oxide and silicon carbide fine powders used in the present invention preferably have an average of 10μ
The particle size is preferably 2 μm or less, more preferably 2 μm or less. It is desirable that the sintered body does not contain more than a specified amount of aluminum and boron, but both are 0.1% by weight.
If the content is below, a high thermal conductivity of 0.6 cal/cm・sec・℃ or more can be obtained. If more aluminum and boron are contained than above, the thermal conductivity will be 0.6cal/
It becomes smaller than cm・sec・℃. Furthermore, when it is desired to obtain a thermal conductivity of 0.5 cal/cm·sec·°C or higher, it is preferable to sinter silicon carbide using a powder whose main component is α-type SiC. Sintering of silicon carbide powder containing beryllium oxide is preferably performed in a non-oxidizing atmosphere. In an oxidizing atmosphere, the surface of silicon carbide powder is oxidized, making it difficult to obtain a high-density sintered body. The preferred sintering temperature is 1850-2500°C, more preferably 1900-2300°C. If the temperature is lower than 1850°C, it is difficult to obtain a high-density sintered body. 2500℃
If the temperature is higher, the sublimation of silicon carbide will be intense, the sintered body will be overfired, and it will be difficult to obtain dense porcelain. In the hot press method, which presses the sample under high pressure during sintering, the pressurizing load depends on the material of the die used. Graphite dies can apply pressure up to approximately 700 kg/cm ² . However, a high-density sintered body can be obtained without applying such a large pressure. The normal pressure is
It is 100-300Kg/ ^cm2 . In addition, by using silicon carbide powder with submicron particle size,
A dense sintered body (90% of the theoretical value) can be obtained without hot pressing. The optimum value of the sintering time is determined by the particle size of the raw powder, the temperature, and the load applied during sintering. Generally, the smaller the particle size of the raw material powder, the higher the temperature, and the greater the load applied during sintering, the faster a high-density sintered body can be obtained. Example 1 0.1% beryllium oxide powder with a particle size of 10 μm or less is added to silicon carbide powder with an average particle size of 2 μm, about 0.2% by weight of free carbon, about 0.02% by weight of aluminum, and traces of boron.
~20% by weight was added and mixed. Next, a pressure of 1000 Kg/cm ² was applied to the mixed powder at room temperature to form a compact. The shaped body has a density of 1.60-1.67 g/cm ³ (relative density of 50-52% of the theoretical density of silicon carbide). Next, the molded body is placed in a graphite die and the degree of vacuum is 1×10 ^-5 ~
Sintering was performed by hot pressing in 1×10 ⁻³ torr. The sintering pressure is 300Kg/ ^cm2 , and heating starts from room temperature.
The temperature was raised to 2000°C in about 2 hours, held at 2000°C for 1 hour, and then the heating power was turned off and allowed to cool. pressure is temperature
It was lifted after the temperature dropped below 1500℃. The relationship between the characteristics of the silicon carbide sintered body produced as described above and the beryllium content is shown in FIGS. 1 to 4. From the results shown in Figures 1 to 3, when the amount of beryllium contained in the silicon carbide sintered body is in the range of 0.1 to 3.5% by weight, it has high density, high thermal conductivity, high electrical resistivity,
A sintered body having a low coefficient of thermal expansion (4×10 ^-6 /°C or less) can be obtained. Example 2 A mixed powder obtained by adding 4% by weight of beryllium oxide powder to the same silicon carbide powder as in Example 1 was used to obtain a sintered body by hot pressing. The content of beryllium contained in the sintered body at this time was about 1% by weight. In this example, sintered bodies were produced by changing hot pressing conditions. Table 1 shows the relationship between the properties of the obtained sintered body and the hot pressing conditions. By sintering at a temperature of 1850 to 2500°C and a pressure of 100 kg/cm ² or more, it has a density of 90% or more of the theoretical density.
A sintered body with a thermal conductivity of 0.4 cal/cm·sec·°C or higher, an electrical resistivity of 10 ¹¹ Ωcm or higher, and a thermal expansion coefficient of 3.3×10 ^-6 /°C was obtained.

【table】

[Table] FIG. 4 is a diagram showing the relationship between relative density and thermal conductivity from Examples 1 and 2. As shown in the figure, the thermal conductivity can be improved by setting the relative density to 90% or more.
A value of 0.4cal/cm・sec・℃ or more can be obtained. % in the figure is beryllium content. Example 3 The same silicon carbide powder as in Example 1 was used, and the sintered body of silicon carbide was made in the same manner as in Example 1, with the amount of beryllium oxide added being 3% by weight, and the atmosphere during sintering being argon gas and helium. Manufactured using gas and nitrogen gas. The content of beryllium in the obtained sintered body was 0.9% by weight. Its properties were almost the same as those of the sintered body of Example 1 with a beryllium content of 1% by weight. Example 4 After adding and mixing 2% by weight of beryllium oxide to the silicon carbide powder of Example 1 having an average particle size of 0.2 to 2.0 μm, a sintered body was produced by hot pressing in the same manner as in Example 1. Table 2 shows the relationship between the average particle size of the silicon carbide raw material powder and the relative density of the obtained sintered body. If the average particle size of the silicon carbide raw material powder is 10 μm or less, the sintered body will be densified to a relative density of 95% or more. Further, the sintered body whose relative density was densified to 95% or more showed characteristics similar to those of Example 1 with a beryllium content of 0.4% by weight. In a sintered body in which the average particle size of the silicon carbide raw material powder is larger than 10 μm and densification has not progressed sufficiently, the thermal conductivity is 0.2 cal/
The mechanical strength was 10 Kg/mm ² or less, which was a small value.

[Table] Example 5 2% by weight of beryllium oxide powder was added to the same silicon carbide powder as in Example 1, and carbon black (fine powder with a particle size of 0.1 μm or less) was added as an impurity by 0.3 to 1 weight per silicon carbide. % was added to form a mixed powder, and a sintered body was obtained by hot pressing.
Table 3 shows the relationship between the amount of carbon black added and the characteristics of the sintered body. When the amount of carbon black added exceeds 0.5% by weight, the thermal conductivity decreases rapidly and the electrical resistivity decreases to 10 ⁶ Ω.・It becomes cm.

[Table] Example 6 In this example, in place of the carbon black added as an impurity in Example 5, aluminum nitride powder (fine powder with a particle size of 2 μm or less) was added to silicon carbide to prepare a mixed powder. Table 4 shows the relationship between the aluminum content and the properties of the sintered body. When the aluminum content exceeds 0.1% by weight, the thermal conductivity decreases to 0.6 cal/cm・sec・℃ and the electrical resistivity decreases. becomes significantly smaller.

[Table] Example 7 In this example, in place of the carbon black added as an impurity in Example 5, boron nitride powder (fine powder with a particle size of 5 μm or less) was added to silicon carbide to prepare a mixed powder. Table 5 shows the relationship between the boron content and the properties of the sintered body. When the boron content exceeds 0.1% by weight, the thermal conductivity decreases significantly.

[Table] Figure 5 shows C for Examples 5, 6 and 7.
FIG. 2 is a diagram summarizing the relationship between Al and B contents and thermal conductivity. As shown in the figure, it is clear that C, Al, and B all significantly lower the thermal conductivity. Comparative Example 1 Example 1 without adding additives to silicon carbide powder
A sintered body was obtained by the hot pressing method in the same manner as above. The properties of the sintered body are as shown in Table 7, and since it is not densified, the values of thermal conductivity, electrical resistivity, and mechanical strength are all small.

[Table] Thermal conductivity and electrical resistivity were measured at room temperature. Thermal expansion coefficient was an average value between room temperature and 300°C. Comparative Example 2 2% by weight of aluminum oxide was added and mixed as an additive to silicon carbide powder. Mixed powder is Example 1
After forming a molded body in the same manner as above, a sintered body was obtained by hot pressing. The properties of the sintered body are shown in Table 8, and it is sufficiently densified and has high mechanical strength, but its thermal conductivity and electrical resistivity are both low. Furthermore, properties similar to those shown in Table 8 were also exhibited when aluminum carbide, aluminum nitride, and aluminum phosphate were used as additives.

[Table] Thermal conductivity and electrical resistivity are measured at room temperature.Thermal expansion coefficient is the average value between room temperature and 300°C.Example 9 As a specific application example of the electrically insulating substrate made of the sintered body of the present invention, Example 1 A semiconductor power module using the silicon carbide sintered body with a beryllium content of 0.5% by weight as a substrate will be explained. 7th
The figure is an assembled sectional view of a conventional structure. A spacer 3 is provided to insulate the organic insulator 5 and the alumina substrate 7 between the conductor 4 and the heat sink 6, and between the heat sink 6 and the metal support plate 8, and to alleviate the strain caused by the difference in thermal expansion coefficient between the silicon element 1 and the heat sink 6.
is interposed. FIG. 6 is an assembled sectional view of a module using an insulating substrate according to the present invention. The substrate 15 is directly brazed to the silicon element 11 and has a very simple structure. The above semiconductor device was kept at -60℃ for 30 minutes, then brought to room temperature and kept for 5 minutes, and then heated to 125℃ for 30 minutes.
A heat cycle was applied for a minute hold. In the conventional semiconductor device (Figure 7), cracks appeared on the board after 20 heat cycles, and peeling occurred at the soldered areas. No abnormality was observed in the semiconductor device according to the present invention (FIG. 8) even after 150 heat cycles. The silicon carbide sintered body according to the present invention is characterized by being dense and having high thermal conductivity, high electrical resistivity, and low coefficient of thermal expansion. Therefore, as described above, it is suitable as a substrate for a semiconductor device, a member that requires heat resistance and oxidation resistance, a member that requires thermal shock resistance, and a member that requires high strength at high temperatures.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the beryllium content and the relative density of the sintered body, Figure 2 shows the relationship between the beryllium content and the thermal conductivity of the sintered body at room temperature, and Figure 3 shows the relationship between the beryllium content and the thermal conductivity of the sintered body at room temperature. Figure 4 shows the relationship between the beryllium content and the electrical resistivity of the sintered body at room temperature. Figure 5 is a diagram showing the relationship between relative density and thermal conductivity, Figure 6 is a diagram showing the relationship between thermal conductivity and amount of impurities, and Figure 7 is a diagram showing the relationship between thermal conductivity and the amount of impurities.
The figure is an assembled sectional view of a conventional silicon semiconductor device, and FIG. 8 is a sectional view of a silicon semiconductor device of the present invention. 1 and 11...silicon element, 2 and 12
... Aluminum lead wire, 3 ... Molybdenum spacer, 4 and 13 ... Conductor, 5 ... Organic insulator, 6 ... Heat sink, 7 ... Alumina substrate,
8... Support plate, 9, 10 and 14... Solder, 1
5...Silicon carbide sintered body substrate.

Claims (1)

[Claims] 1. High thermal conductivity carbonization characterized by beryllium oxide consisting of 0.1 to 3.5% by weight of beryllium, 0.1% by weight or less of aluminum, 0.1% by weight or less of boron, 0.4% by weight or less of free carbon, and the balance substantially consisting of silicon carbide. Silicon sintered body.