Composite substrate
This composite substrate has a single-crystal semiconductor thin film ( 13 ) provided to at least the front surface of an inorganic insulating sintered-body substrate ( 11 ) having a thermal conductivity of at least 5 W/m·K and a volume resistivity of at least 1×10 8 Ω·cm. The composite substrate also has, provided between the inorganic insulating sintered-body substrate ( 11 ) and the single-crystal semiconductor thin film ( 13 ), a silicon coating layer ( 12 ) comprising polycrystalline silicon or amorphous silicon. As a result of the present invention, metal impurity contamination from the sintered body can be inhibited, even in a composite substrate in which a single-crystal silicon thin film is provided upon an inexpensive ceramic sintered body which is opaque with respect to visible light, which exhibits an excellent thermal conductivity, and which further exhibits little loss at a high frequency range, and characteristics can be improved.
1. A composite substrate comprising an inorganic insulating sintered-body substrate having a thermal conductivity of at least 5 W/m·k and a volume resistivity of at least 1×10 8 Ω·cm, and a single-crystal semiconductor thin-film provided on at least a front surface of the inorganic insulating sintered-body substrate, the composite substrate being characterized by having a silicon coating made of polycrystalline silicon or amorphous silicon provided between the inorganic insulating sintered-body substrate and the single-crystal semiconductor thin-film.
2. The composite substrate of claim 1 which is characterized in that the silicon coating covers all of the inorganic insulating sintered-body substrate.
3. The composite substrate of claim 1 which is characterized in that the silicon coating is a high-purity silicon layer formed by sputtering, electron-beam vapor deposition, chemical vapor deposition or epitaxial growth.
4. The composite substrate of claim 1 which is characterized in that the inorganic insulating sintered-body substrate is composed primarily of silicon nitride, aluminum nitride or sialon.
5. The composite substrate of claim 1 which is characterized in that the single-crystal semiconductor thin-film is single-crystal silicon.
6. The composite substrate of claim 1 which is characterized by further comprising, between the inorganic insulating sintered-body substrate and the silicon coating, a silicon nitride coating formed by chemical vapor deposition.
7. The composite substrate of claim 1 which is characterized by further comprising, between the silicon coating and the single-crystal semiconductor thin-film, at least one intermediate insulating layer made of a material selected from the group consisting of silicon oxide, silicon nitride, aluminum nitride and sialon.