JPS6232154B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sintered body for a heat sink and a method for manufacturing the same. In recent years, semiconductor devices used in high electric fields and large current densities have been put into practical use, and especially in devices such as semiconductor lasers and impact devices, where the power consumption density in the active region is high, the amount of heat generated by the device is large. It is necessary to take some kind of measure to prevent the temperature of the device from rising. As a material for this purpose, materials that can be used as heat sinks and have high thermal conductivity are attracting attention. 1st
The table shows the thermal conductivity at room temperature of various single crystal materials, including Cu and diamond, which are currently used as heat sinks in semiconductor devices. Diamonds are classified into several types depending on their crystallinity and impurity content. Among these, the a-type material in particular has the highest thermal conductivity among existing materials at around room temperature. However, the production of natural A-type diamonds is extremely small. In addition, in order to use it as a semiconductor device, it must have a certain size and thickness, and processing a naturally irregularly shaped one would be extremely expensive. Although BeO has the highest thermal conductivity among oxides, it has the disadvantage of being toxic to the human body. Cu is cheap and

【table】

[Table] Semiconductor devices used as heat sinks have the disadvantage of shortening the life of the device due to rapid diffusion in the Au and Pt electrodes. Among the materials shown in Table 1, diamond has high thermal conductivity, along with cubic BN, and is attracting attention as a heat sink material. Although some efforts have been made to use single crystal diamond as a heat sink material, its primary drawback is its high cost.
If this could be sintered into a polycrystalline material and made into a certain shape and size at low cost, it would be a promising material for heat sinks. From this point of view, the inventors have made various prototypes of diamond sintered bodies. Diamond is the hardest substance, and it is extremely difficult to obtain a completely dense sintered body made of pure diamond. It is considered impossible that a sintered body made only of pure diamond will be produced industrially in the near future. This is because high pressures and temperatures that are industrially unacceptable are required, and revolutionary improvements in the materials used in sintering equipment are necessary for this purpose. The present invention has been developed in view of the above. That is, the sintered body for a heat sink of the present invention is characterized in that it contains 90 to 40% diamond by volume, with the remainder mainly consisting of aluminum nitride, and is sintered in the diamond stability range. In addition, the method for manufacturing a sintered body for a heat sink of the present invention is such that the diamond powder and oxygen content are 1% by weight.
Diamond is made by mixing the following powders mainly consisting of aluminum nitride powder, molding the mixture in powder form or by molding, and then sintering it under high pressure and high temperature using ultra-high pressure equipment. 90 of
~40%, with the remainder mainly consisting of aluminum nitride. As mentioned above, the inventors attempted to improve the sinterability by mixing diamond with other materials with excellent thermal conductivity as a way to solve the difficulties in manufacturing a sintered body made only of diamond. . Table 1 shows the thermal conductivity of materials that can be combined with diamond.
I chose AlN. AlN is said to have a thermal conductivity close to that of BeO, and is a material that is expected to be used alone as a heat sink. with diamonds
If a dense AlN composite sintered body can be obtained, an even better product should be obtained. In the sintered body according to the present invention, the amount of diamond mixed is preferably 90 to 40% by volume of the total. If the amount of AlN added is less than 10% by volume, the effect of improving sinterability is not sufficient. In addition, the thermal conductivity of a composite material is influenced by its volumetric mixing ratio and structure, and if the amount of diamond is less than 40% by volume, the high thermal conductivity of diamond will not be fully exhibited, and the thermal conductivity of the sintered body will be the same as that of AlN. It will be close. The method for manufacturing the sintered body of the present invention is to mix diamond powder and AlN powder with a low oxygen content in a predetermined ratio, press the mixture or fill it in powder form in a container made of graphite or metal, and then heat it in a vacuum furnace. After the powder is heated to a high temperature to remove the gas contained in the powder, it is charged into an ultra-high pressure device such as a belt type or girdle type and sintered under high pressure and high temperature. A graphite cylinder is used as the heating element, and an insulating material such as talc or NaCl is packed inside the cylinder, which encloses a container of diamond mixed powder to be sintered.
It is desirable to place a pressure medium such as pyroferite around the graphite heating element, and to set the pressure and temperature conditions for sintering within the diamond stability region shown in Figure 1, but this equilibrium line is not necessarily accurate. It is not fully understood and is only a guideline. In FIG. 1, A indicates the diamond stability region, and B indicates the graphite stability region. The following points are considered to be the reasons why the sinterability of diamond is improved in the composite sintered body in which AlN is added to diamond according to the present invention. AlN has a lower rigidity than diamond,
When the rigidity is G, the theoretical shear strength expressed by τmax=G/30 is about 500 Kg/mm ² . If the sintered body of the present invention is manufactured under a pressure of 50 Kb, this is approximately equal to the theoretical shear strength of AlN, and AlN particles can easily deform and flow under such high pressure. become. Therefore, it is thought that when AlN particles are mixed with diamond and pressurized, the AlN particles are first deformed and flowed by the external pressure, making it easier to uniformly transmit pressure to the diamond particles. For the reasons mentioned above, diamond
The combination of AlN improves sinterability compared to the case of diamond alone. As mentioned above, such a mixing effect of AlN is clearly observed when the amount of AlN added is 10% or more by volume, but if the amount added is more than 20%, AlN definitely invades between individual diamond particles. , the effect is remarkable. In this case, the sintered body also has a continuous structure in which AlN acts as a bonding phase for diamond. The AlN raw material used in the present invention needs to have as little oxygen content as an impurity as possible. Oxygen in AlN reduces the thermal conductivity of AlN itself and also inhibits sinterability with diamond. As a result of experiments, it became clear that when the oxygen content of the AlN used exceeds 1% by weight, the thermal conductivity of the sintered body decreases significantly. In addition, the sintered body of the present invention contains a material having relatively high thermal conductivity within a range that does not significantly reduce the thermal conductivity of the sintered body.
Compounds other than AlN, such as SiC, WC, B ₄ C, etc., or metals such as Mo, W, Ta, Nb, and small amounts of Fe, Co,
It may also contain Ni, Cu, and Mn. Examples will be described below. Example 1 Artificial diamond powder for grinding with an average particle size of 15μ and AlN powder with an average particle size of 5μ are 80% and 20% by volume, respectively.
and mixed using a V-type blender. The AlN powder used was obtained by nitriding pure Al powder with a purity of 99.99% in high purity N ₂ gas, and the oxygen analysis value was 0.5%. 2% camphor was added to this mixed powder, and the outer diameter was 10mm under a pressure of 1ton/ ^cm2.
It was molded to a thickness of 1.5 mm. The stamped body was placed in a stainless steel container and heated to 1100°C under a vacuum of 10 ^-5 mmHg in a vacuum furnace to perform degassing treatment. This is charged into a girdle-type ultra-high pressure device, and at a pressure of 60Kb.
After heating to 1300°C and holding for 20 minutes, the temperature was lowered and the pressure was gradually lowered. The obtained sintered body has an outer diameter of approximately 10 mm,
It is approximately 1mm thick. For comparison, a 100% diamond material without AlN was sintered at 60 Kb and held at 1600°C for 20 minutes using the same diamond raw material. The AlN-added sintered body of the present invention is a dense sintered body, and when examined by X-ray diffraction, nothing other than diamond and AlN was detected, but the 100% diamond one was sufficiently sintered. However, trace amounts of graphite were detected by X-ray diffraction. The upper and lower surfaces of the sintered body of the present invention were flat-polished using a diamond grindstone, and the thermal conductivity was measured using a steady-state temperature gradient method using an electron beam as a heat source.As a result, the thermal conductivity was 1.5 cal/cm. A measurement value of sec.°C was obtained. Example 2 Using the same raw materials as those used in Example 1, a second
Each powder was blended into the composition shown in the table. Thereafter, a sintered body was prepared in the same manner as in Example 1, and its thermal conductivity was measured. The results are shown in Table 2.

【table】 [Brief explanation of the drawing]

FIG. 1 relates to the manufacturing conditions of the sintered body of the present invention and shows the stable existence region on the pressure and temperature phase diagram of diamond. A...Diamond stability area, B...Graphite stability area.

Claims (1)

[Claims] 1 Contains 90 to 40% of the total diamond by volume, and the remainder mainly consists of aluminum nitride,
A sintered body for a heat sink characterized by being sintered in the diamond stability range. 2 Diamond content is 90 to 40 of the total volume
%, and the binder phase mainly composed of aluminum nitride has a continuous structure in the sintered body. 3 Diamond powder and oxygen content 1% by weight
Diamond is made by mixing the following powders mainly consisting of aluminum nitride powder, molding the mixture in powder form or by molding, and then sintering it under high pressure and high temperature using ultra-high pressure equipment. 90 of
A method for producing a sintered body for a heat sink, characterized in that the aluminum nitride contains aluminum nitride by 40% and the remainder mainly consists of aluminum nitride.