Patent ID: 8092914

Claim:
A heat sink substrate having a mount surface on which a semiconductor device is to be mounted, comprising a composite structure composed of a three dimensional network structure of SiC ceramic having pores infiltrated with Si, the heat sink substrate having a thermal conductivity of not less than 200 W/m·K and being configured to have an oxygen content of not greater than 7 ppm, wherein the oxygen content is selected so as to increase the efficiency of heat conduction from the semiconductor device to the heat sink substrate, and the number of defects of at least one of the following types (i) to (iii) present in a unit area of the mount surface is not greater than one defect per 50 cm 2 : (i) a vacant pore having a diameter of 0.3 to 1.0 mm, or a Si block filling the vacant pore with Si having a diameter of 0.3 to 1.0 mm; (ii) a rough surface portion constituted by a plurality of minute vacant pores gathering in a surface direction, and having a diameter of 1.0 to 2.0 mm; and (iii) a crack-like portion constituted by a plurality of minute vacant pores linearly connected to one another, and having a length of 1.0 to 2.0 mm.