Methods for forming mos devices with raised source/drain regions

Abstract

A method includes forming a first gate stack of a first device over a semiconductor substrate, and forming a second gate stack of a second MOS device over the semiconductor substrate. A first epitaxy is performed to form a source/drain stressor for the second MOS device, wherein the source/drain stressor is adjacent to the second gate stack. A second epitaxy is performed to form a first silicon layer and a second silicon layer simultaneously, wherein the first silicon layer is over a first portion of the semiconductor substrate, and is adjacent the first gate stack. The second silicon layer overlaps the source/drain stressor.