Patent ID: 6900133

Claim:
A method of etching variable depth features in a crystalline substrate, comprising the following steps, performed in the following order: a) providing a structure including, from top to bottom, a first patterned photoresist layer, a hard mask layer, and a crystalline substrate; b) pattern etching said hard mask layer by exposing said structure to a plasma generated from a first plasma source gas which selectively etches said hard mask layer relative to said crystalline substrate, whereby a plurality of openings are formed in said hard mask layer, and whereby portions of an upper surface of said crystalline substrate are exposed through said openings; c) removing said first photoresist layer; d) providing a second patterned photoresist layer overlying said structure, whereby a portion of said second patterned photoresist layer covers at least one opening formed in said hard mask layer; e) pattern etching said crystalline substrate using said second patterned photoresist layer as a mask, whereby at least one deep feature is formed in said crystalline substrate; f) removing said second photoresist layer; g) pattern etching said crystalline substrate using said patterned hard mask layer, by exposing said structure to a plasma generated from a second plasma source gas which selectively etches said crystalline substrate relative to said hard mask layer, whereby at least one shallow feature is formed in said crystalline substrate, and wherein a sidewall of said at least one shallow feature has a surface roughness of about 200 nm or less.