Patent ID: 7341952

Claim:
A method for etching a deep trench in a substrate, comprising the steps of: forming a multi-layer hard mask structure overlying the substrate, comprising a first hard mask layer and at least one second hard mask layer disposed thereon, wherein the first hard mask layer is composed of a first boro-silicate glass layer and an overlying first undoped silicon glass layer and the second hard mask layer is composed of a second boro-silicate glass layer and an overlying second undoped silicon glass layer; forming a polysilicon layer overlying the multi-layer hard mask structure; etching the polysilicon layer to form an opening therein and expose a portion of the multi-layer hard mask structure; successively etching the multi-layer hard mask structure and the underlying substrate under the opening to simultaneously form the deep trench in the substrate and remove the polysilicon layer; and removing the multi-layer hard mask structure.