Silicon-on-sapphire integrated circuit and method of making the same

Abstract

An SOS integrated circuit includes a plurality of spaced islands of single-crystalline silicon on a surface of a sapphire substrate. A conformal layer of silicon oxide is on the surface of the sapphire substrate between the islands and extends along a portion of the side surfaces of the islands. A layer of polycrystalline silicon is over the silicon oxide layer and extends over the side surface and at least a portion of the top surface of the islands. A separate field-effect transistor is on each island and includes source and drain regions spaced by a channel region and a channel dielectric layer over the channel region. The polycrystalline silicon layer may extend over the channel dielectric to serve as the gate of the transistor. The method of making the circuit includes depositing the silicon oxide layer over the sapphire substrate surface and the islands, and applying a layer of a negative photoresist over the silicon oxide layer. Light is directed through the sapphire substrate to expose portions of the photoresist layer which are not over the islands. The unexposed portions of the photoresist layer are removed to expose portions of the silicon oxide layer which are over the islands. These exposed portions of the silicon oxide layer are removed with a suitable etchant.