Patent ID: 6602759
Filing Date: 2003-08-05
Classification: H01L

Abstract:
A method for forming an isolation trench in a semiconductor structure having a silicon-on-insulator substrate comprising:forming a trench having a bottom and sidewalls in the semiconductor structure; depositing an undoped polysilicon layer on the bottom and the sidewalls of the trench and on a surface of a semiconductor region adjacent to the trench, said semiconductor region adjacent to the trench comprising a multiple layer structure that includes a silicon layer, a pad oxide layer above the silicon layer, a silicon nitride layer above the pad oxide layer, and a doped polysilicon layer above the silicon nitride layer, all layers of the multiple layer structure residing above a level of the bottom of the trench, the undoped polysilicon layer deposited such that a substantial portion of the trench is left unfilled; and oxidizing the undoped polysilicon layer to form a thermal oxide that fills the trench and thereby avoids forming a birds-beak formation of the thermal oxide above the sidewalls of the trench and avoids reduction in active device area in said adjacent semiconductor region.