Method of fabricating semiconductor device and semiconductor device fabricated thereby

A method of fabricating a semiconductor device comprising the steps of:

• Step 1:
• providing a semiconductor substrate, forming shallow trench isolations in SRAM regions in the semiconductor substrate, and forming a mask layer on the semiconductor substrate;
• Step 2:
• patterning the mask layer and etching the semiconductor substrate to form recesses in the semiconductor substrate;
• Step 3:
• epitaxial growing a first SiGe seed layer with a constant Ge content in the recesses;
• Step 4:
• epitaxial growing a second SiGe layer with a constant Ge content on the first SiGe seed layer, wherein the Ge content of the second SiGe layer is higher than that of the first SiGe seed layer;
• Step 5:
• epitaxial growing a third SiGe layer with a constant Ge content on the second SiGe layer, wherein the Ge content of the third SiGe layer is lower than that of the second SiGe layer;
• Step 6:
• forming a cap layer on the third SiGe layer.