Patent ID: 7629211

Claim:
A method of forming a field effect transistor, comprising: providing a semiconductor substrate, a gate electrode being formed above said semiconductor substrate; forming at least one cavity in said substrate adjacent said gate electrode; and forming a strain-creating element in said at least one cavity, said strain-creating element comprising: a compound material comprising a first chemical element and a second chemical element, wherein said first chemical element comprises one of germanium and carbon, said second chemical element comprises silicon, and said semiconductor substrate comprises said second chemical element; a first portion and a second portion, wherein said second portion is located above said first portion; a first concentration ratio between a concentration of said first chemical element in said first portion and a concentration of said second chemical element in said first portion; and a second concentration ratio between a concentration of said first chemical element in said second portion and a concentration of said second chemical element in said second portion, wherein said first concentration ratio is smaller than said second concentration ratio and wherein a ratio between a concentration of said first chemical element and a concentration of said second chemical element increases in a vertical direction with increasing distance from a bottom surface of said at least one cavity formed in said substrate.