Patent ID: 7544997

Claim:
A method for forming a semiconductor device comprising: forming a recess in a source region and a recess in a drain region of the semiconductor device; forming a first semiconductor material layer in the recess in the source region and a second semiconductor material layer in the recess in the drain region, wherein each of the first semiconductor material layer and the second semiconductor material layer are formed using a stressor material having a first ratio of an atomic concentration of a first element and an atomic concentration of a second element, wherein the first element is silicon and a first level of concentration of a doping material; forming a third semiconductor material layer overlying the first semiconductor material layer and a fourth semiconductor material layer overlying the second semiconductor material layer, wherein each of the third semiconductor material layer and the fourth semiconductor material layer have a second ratio of the atomic concentration of the first element and the atomic concentration of the second element, wherein the second ratio is higher than the first ratio and wherein each of the third semiconductor material layer and the fourth semiconductor material layer have a second level of concentration of the doping material, wherein the second level of concentration of the doping material is higher than the first level of concentration of the doping material; and forming a fifth semiconductor material layer overlying the third semiconductor material layer and a sixth semiconductor material layer overlying the fourth semiconductor material layer, wherein each of the fifth semiconductor material layer and the sixth semiconductor material layer have a third ratio of the atomic concentration of the first element and the atomic concentration of the second element, wherein the third ratio is lower than the second ratio and wherein each of the fifth semiconductor material layer and the sixth semiconductor material layer have a third level of concentration of the doping material, wherein the third level of concentration of the doping material is higher than the second level of concentration of the doping material.