A p-type field effect transistor (PFET) and an n-type field effect
transistor (NFET) are formed by patterning of a gate dielectric layer, a
thin silicon layer, and a silicon-germanium alloy layer. After formation
of the source/drain regions and gate spacers, silicon germanium alloy
portions are removed from gate stacks. A dielectric layer is formed and
patterned to cover an NFET gate electrode, while exposing a thin silicon
portion for a PFET. Germanium is selectively deposited on semiconductor
surfaces including the exposed silicon portion. The dielectric layer is
removed and a metal layer is deposited and reacted with underlying
semiconductor material to form a metal silicide for a gate electrode of
the NFET, while forming a metal silicide-germanide alloy for a gate
electrode of the PFET.