Patent ID: 7592265

Claim:
A method of trimming a hard mask layer, comprising: providing a substrate and a hard mask layer on said substrate; forming a multi-layer stack comprising at least a top photo resist layer, a silicon photo resist layer, and a bottom photo resist layer on said hard mask layer; patterning said top photo resist layer; etching said silicon photo resist layer by using said patterned top photo resist layer as an etching mask to pattern said silicon photo resist layer to form a first opening of a first width on the bottom thereof; removing said top photo resist layer; etching said bottom photo resist layer sequentially by using said patterned silicon photo resist layer as an etching mask; etching said hard mask layer sequentially by using said patterned bottom photo resist layer as an etching mask to form a second opening of said first width; and trimming said hard mask layer to make said second opening with a second width larger than said first width.