| 摘要 |
PURPOSE:To obtain a composite substrate which can block crystal defects being created and electrical characteristics being deteriorated, by thermally welding a semiconductor layer whose surface is sufficiently smoothed by polishing and is covered by an oxide film, to an insulating substrate whose surface is also sufficiently smoothed. CONSTITUTION:On the Si substrate 1 which has As added at a high concentration and is polished into a mirror face, an Si layer 2 is epitaxially grown, and then is covered by the thermal oxide film 3. Onto the surface polished into a mirror face of the other SiO2 substrate 4, the substrate 1 is overlapped with the thermalo oxide film 3 contacted. They are united by thermal welding for about one hour at 100 deg.C, 500g/cm<2>. Only the Si 1 having As added at a high concentration is selectively etched away by mixed acid of hydrofluoric acid : nitric acid : acetic acid =1:3:8. In this construction, a problem forming imperfect crystal layer at the initial stage of the epitaxial growth due to the effects which may result from substrates with different crystal structure, does not occur. Since the surface of the Si layer 2 is protected with the oxide film 3 before the thermal welding, unstable interface forming owing to contamination at the thermal welding can be avoided, and thus a substrate in which high-speed and high-density elements can be formed, can be provided.
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