Patent ID: 8610175

Claim:
A method for manufacturing a semiconductor device, comprising: forming a recess in a Si substrate, the recess being used for forming a source region or a drain region; forming a first SiGe layer on the bottom of the recess, wherein the content of Ge in the first SiGe layer is gradually increased from bottom to top of the first SiGe layer, and the first SiGe layer has a thickness less than the depth of the recess; subsequently forming a SiGe seed layer on areas of sidewalls of the recess that are not covered by the first SiGe layer, the SiGe seed layer having a constant content of Ge; and forming a second SiGe layer having a uniform content of Ge on the first SiGe layer, wherein the content of Ge in the SiGe seed layer is less than the content of Ge in the second SiGe layer, and the content of Ge at the upper surface of the first SiGe layer is less than or equal to the content of Ge in the second SiGe layer.