Patent ID: 6908846

Claim:
A method for controlling a plasma etch process in a plasma processing chamber, comprising: introducing a substrate having thereon a layer stack into said plasma processing chamber, said layer stack including a first layer disposed above an end-point generating layer; etching through said first layer and at least partially through said end-point generating layer while monitoring an absorption rate of a light beam traversing an interior portion of said plasma processing chamber, wherein said endpoint generating layer is selected from a material that produces a detectable change in said absorption rate when etched, said end-point generating layer being characterized by at least one of a first characteristic and a second characteristic, said first characteristic being an insufficient thickness to function as an etch stop layer for said etching, said second characteristic being an insufficient selectivity to etchants employed to etch through said first layer to function as said etch stop layer; and generating an end-point signal upon detecting said detectable change.