Generally, in a semiconductor element such as a semiconductor laser element or high-frequency element that is used for optical communication or the like, it is very important how to release the heat generated from the element efficiently, for preventing malfunctions or the like. In recent years, higher outputs, higher speeds, and higher integration of the elements have accompanied progress in semiconductor technology, and the requirements for heat dissipation have grown increasingly stringent. Therefore, generally, also for a heat dissipation component such as a heat sink, a high thermal conductivity is required, and copper (Cu), which has a high thermal conductivity of 390 W/mK, is used.
Meanwhile, each semiconductor element has increased in dimensions accompanying higher outputs, and the problem of mismatch in thermal expansion between the semiconductor element and the heat sink to be used for heat dissipation has become obvious. To solve these problems, the development of a heat sink material that achieves both the high thermal conduction characteristic and the matching of the coefficient of thermal expansion with the semiconductor element are required. As such a material, a composite body of metal and ceramic, for example, a composite body of aluminum (Al) and silicon carbide (SiC), has been proposed (Patent Document 1).
However, in the Al—SiC composite body, the thermal conductivity is 300 W/mK or lower even when the condition is optimized, and the development of a heat sink material having a thermal conductivity higher than the thermal conductivity of copper is required. As such a material, a metal-diamond composite body having a high thermal conductivity and a thermal expansion coefficient close to that of the semiconductor element material by the combination of the high thermal conductivity of diamond and the high coefficient of thermal expansion of metal has been proposed (Patent Document 2).
Further, in Patent Document 3, by forming β-SiC layers on surfaces of diamond particles, the generation of a metal carbide with a low thermal conductivity that is formed at the time of composition is suppressed, and the wettability with molten metal is improved, so that the thermal conductivity of a metal-diamond composite body to be obtained is improved.
Furthermore, since diamond is a very hard material, the metal-diamond composite body obtained by the composition with metal is also very hard, and is a material that is difficult to machine. Therefore, the metal-diamond composite body can hardly be machined by a usual diamond tool, and in order to use the metal-diamond composite body for small-size heat sinks having various shapes, the problem is how to perform the shape machining at low costs. For such a problem, laser machining and water jet machining have been considered, and further, a machining method by electric discharge machining has also been considered because the metal-ceramic composite body is electrically conductive.    Patent Document 1: JP H9-157773 A    Patent Document 2: JP 2000-202126 A    Patent Document 3: JP2007-518875 A