Planarization process for IC trench isolation using oxidized polysilicon filler

A method of planarizing a face of a silicon substrate comprising:

• etching said face to form flat active area mesas and trenches;
• depositing a conformal coating of a silicon oxide over said face, in a thickness such that the level of the top of the oxide in the trenches is at about the same level as the top of the active area mesas, forming depressions above said trenches;
• depositing a layer of polysilicon over the conformal oxide coating, said polysilicon having a thickness about half the depth of the depressions above said trenches;
• patterning the polysilicon layer with a photoresist to form resist blocks in the depressions above said trenches;
• etching said polysilicon to leave polysilicon segments remaining in the areas beneath the resist blocks;
• annealing the polysilicon to convert said polysilicon to oxide;
• polishing the face of the semiconductor substrate with oxide filled trenches to the level of the tops of the active areas so as to produce a substantially planar surface.