Patent ID: 7238568

Claim:
A process of fabricating a trench semiconductor device comprising: providing a semiconductor material; forming a mask layer on a surface of said semiconductor material; forming a opening in said mask layer; forming a trench in said semiconductor material by etching said semiconductor material through said opening; forming an oxide lining on a bottom and sidewalls of said trench; depositing a first polysilicon layer in said trench; etching said first polysilicon layer such that a remaining portion of said first polysilicon layer remains over said oxide lining at the bottom of said trench; removing said oxide lining except for a remaining portion of said oxide lining that is adjacent said remaining portion of said first polysilicon layer; anisotropically etching a top surface of said remaining portion of said first polysilicon layer so as to depress said top surface to a level below a top surface of said remaining portion of said oxide lining; heating said device so as to form a first oxide layer on said top surface of said first polysilicon layer and a second oxide layer on exposed portions of said sidewalls of said trench; removing said first oxide layer while leaving a portion of said second oxide layer on the sidewalls of said trench; and depositing a second polysilicon layer in said trench.