Patent ID: 7759199

Claim:
A method of selectively forming semiconductor material, comprising: providing a substrate within a chemical vapor deposition chamber, the substrate comprising insulating surfaces and single-crystal semiconductor surfaces, wherein the single-crystal semiconductor surfaces include a recess having a sidewall immediately adjacent a transistor channel; and selectively forming a semiconductor stressor in the recess, wherein the semiconductor stressor is graded such that an upper portion of the semiconductor stressor within the recess has a higher amount of strain than lower portions and wherein the upper portion of the semiconductor stressor extends within the recess to the sidewall of the recess; wherein selectively forming comprises: depositing semiconductor material over the insulating surfaces and the single-crystal semiconductor surfaces; selectively removing non-epitaxial semiconductor material from the insulating surfaces, and selectively removing epitaxial material from the sidewall of the recess while leaving epitaxial material at a bottom of the recess; and repeating depositing and selectively removing in a plurality of cycles, wherein each cycle adds to a thickness of epitaxial material at a bottom of the recess and wherein a layer of semiconductor material contains a higher concentration of a dopant than an underlying layer of semiconductor material in the recess.