Patent ID: 7078350

Claim:
In a plasma processing system, a method etching a substrate, said substrate having a semi-conductor layer, a first barrier layer disposed above said semi-conductor layer, a low-k layer disposed above said first barrier layer, a third hard mask layer disposed above said low-k layer; a second hard mask layer disposed above said third hard mask layer, and a first hard mask layer disposed above said second hard mask layer, comprising: alternatively etching said substrate with a first etchant and a second etchant, wherein said first etchant has a low selectivity to a first hard mask material of said first hard mask layer, a third hard mask material of said a third hard mask layer, and a first barrier layer material of said first barrier layer, but a high selectivity to a second hard mask material of said second hard mask layer, wherein said second etchant has a high selectivity to said first hard mask material of said first hard mask layer, said third hard mask material of said third hard mask layer, and said first barrier layer material of said first barrier layer, and said second etchant has a low selectivity to said second hard mask material of said second hard mask layer, and wherein said alternatively etching includes etchin artiall tbrou h said low-k layer and said first barrier layer with said second etchant.