Patent ID: 8652969

Claim:
A method of forming a semiconductor structure comprising: providing a stack of a semiconductor substrate and a mask layer having an opening therein, wherein a top surface of said semiconductor substrate is physically exposed at a bottom of said opening; and repeatedly performing a sequence of an etch process and a deposition process on said stack, wherein said etch process removes a semiconductor material at a bottom surface of a trench underlying said opening, and said deposition process deposits a hydrofluorocarbon polymer material on said bottom surface and sidewalls of said trench that is generated from a plasma containing radicals and ions of a hydrofluorocarbon gas, wherein said hydrofluorocarbon polymer material has a first composition at said bottom surface of said trench, said hydrofluorocarbon polymer material has a second composition at said sidewalls of said trench, wherein said second composition is different from said first composition.