Patent ID: 7387930

Claim:
A method, comprising: (a) providing a substrate; (b) forming a trench in said substrate, said trench having sidewalls and a bottom, said trench having an upper region adjacent to a top surface of said substrate and a lower region adjacent to said bottom of said trench, said upper region abutting said lower region; (c) forming a protective layer on said sidewalls and said bottom of said trench, said protective layer comprising a first layer on said sidewalls and bottom of said trench, a second layer on said first layer and a third layer on said second layer; (d) removing said protective layer from said sidewalls in said lower region of said trench and from said bottom of said trench, said first, second and third layers of said protective layer remaining over said sidewalls of said trench in said upper region after said removing said protective layer from said sidewalls in said lower region of said trench and from said bottom of said trench; (e) oxidizing a layer of said substrate exposed in step (d) on said sidewalls in said lower region of said trench and on said bottom of said trench; and (f) removing said layer of said substrate oxidized in step (e) from said lower region of said trench.