Process of making a semiconductor device having regions of insulating material formed in a semiconductor substrate

A process for fabricating a silicon-on-insulator integrated circuit in conjunction with a process for shallow trench isolation is disclosed. The shallow trench isolation is performed to define active regions in the silicon substrate. The active regions are electrically isolated from each other by regions of silicon dioxide formed in the substrate by the shallow trench isolation process. The height of the silicon dioxide regions above the substrate surface defines the combined thickness of the islands of silicon dioxide and the silicon formed over the islands of silicon dioxide. A mask is then formed on the silicon substrate with the regions of silicon dioxide formed therein. The mask defines the regions on the silicon substrate surface on which the islands of silicon dioxide are to be formed. The silicon dioxide islands are formed with the mask in place, and the mask is subsequently removed. Single crystal silicon is formed epitaxially on the structure. This is followed by the deposition of amorphous silicon and recrystallization to form a structure that has islands of insulating silicon dioxide formed in the silicon substrate and below the substrate surface.