Patent ID: 7531461

Claim:
A method of etching a silicon layer on a substrate, comprising: disposing said substrate having said silicon layer in a plasma processing system, wherein said silicon layer comprises: a first sub-layer having a dopant and occupying a first fraction of the thickness of said silicon layer, and a second undoped sub-layer occupying the remaining fraction of the thickness of said silicon layer, said first sub-layer disposed over said second sub-layer, a dopant concentration in said silicon layer changing abruptly between said first sub-layer and said second sub-layer; introducing a first process composition comprising SF 6 and a fluorocarbon gas to said plasma processing system; forming a first plasma from said first process composition in said plasma processing system; exposing said substrate to said first plasma during a first time period sufficient to etch said first sub-layer; introducing a second process composition comprising a halogen containing gas to said plasma processing system, said second process composition being different from said first process composition; forming a second plasma from said second process composition in said plasma processing system; and exposing said substrate to said second plasma during a second time period, following said first time period, sufficient to etch said second sub-layer.