Patent ID: 8034722

Claim:
A method for forming an opening in a composite structure of material layers, comprising: forming a composite structure that does not include an etch stop layer by forming first, second and third material layers sequentially over a substrate, said first, second and third material layers having first, second and third thicknesses, respectively, said third material layer being an uppermost, exposed layer; and patterning to form an opening extending by a depth into said first material layer while removing a removed thickness of said third material layer using an etch process, a ratio of said depth to said removed thickness substantially corresponding to an etch selectivity of said first material layer to said third material layer in said etch process, terminating said etch process based on said removed thickness and without use of an etch stop layer to produce said opening with said depth and having a lowermost bottom surface consisting completely of said first material, said depth being predetermined based upon said removed thickness.