Method for fabricating an isolation structure including a shallow trench isolation structure and a local-oxidation isolation structure

摘要

A method for fabrication a shallow trench isolation (STI) structure by combining uses of a STI process and a local oxidation (LOCAS) process is provided. The method includes forming a first liner oxide layer over a substrate, on which a patterned hard material layer is formed. A hard spacer is formed on each sidewall of the hard material layer. A LOCOS structure is formed on the substrate other than the hard spacer and the hard material layer. Then, the hard spacer is removed to expose a portion of the pad oxide on the substrate. A trench is formed in the substrate on each side of the LOCOS structure. A conformal second liner oxide layer is formed on the inner surface of the trench. The trench is filled with a polysilicon layer, having a surface higher than the substrate surface. A second thermal process is performed to oxidize the polysilicon layer so as to merge the LOCOS structure to cover the surface of the polysilicon layer. The hard material layer is removed to form the isolation structure of the invention.