MOS devices with improved source/drain regions with SiGe

摘要

A semiconductor structure and methods for forming the same are provided. The semiconductor structure includes a semiconductor substrate; a gate stack on the semiconductor substrate; a SiGe region in the semiconductor substrate and adjacent the gate stack, wherein the SiGe region has a first atomic percentage of germanium to germanium and silicon; and a silicide region over the SiGe region. The silicide region has a second atomic percentage of germanium to germanium and silicon. The second atomic percentage is substantially lower than the first atomic percentage.