Patent ID: 6979621

Claim:
A method of forming a trench MOSFET device comprising: providing a silicon substrate of a first conductivity type; depositing a silicon epitaxial layer of said first conductivity type over said substrate, said epitaxial layer having a lower majority carrier concentration than said substrate; forming a body region of a second conductivity type within an upper portion of said epitaxial layer; etching a trench extending into said epitaxial layer from an upper surface of said epitaxial layer, said trench extending through said body region and said trench having trench sidewalls and a trench bottom; forming an oxide region lining said trench, said oxide region comprising a lower segment covering at least the trench bottom and upper segments covering at least upper regions of said trench saidwalls, wherein said oxide region lining said trench is formed by a process comprising: forming a thermal oxide layer within said trench; providing a deposited oxide layer over said thermal oxide layer; forming an etch resistant region in the trench bottom over said deposited oxide layer; and etching said deposited oxide layer where not covered by said etch resistant region; depositing a conductive region within said trench adjacent said oxide region; and forming a source region of said first conductivity type within an upper portion of said body region and adjacent said trench, wherein said lower segment of said oxide region is thicker than said upper segments of said oxide region such that shoulders are established in said oxide region adjacent said conductive region along said trench sidewalls.