Patent ID: 8344447

Claim:
A semiconductor structure comprising: a metal-oxide-semiconductor (MOS) device comprising: a gate dielectric; a gate electrode over the gate dielectric; a first silicon-containing compound layer comprising an element selected from the group consisting essentially of germanium and carbon; a silicon layer on the first silicon-containing compound layer; a second silicon-containing compound layer comprising the element on the silicon layer, wherein the first and the second silicon-containing compound layers have substantially lower silicon concentrations than the silicon layer, wherein the element in the first silicon-containing compound layer has a first concentration higher than a second concentration of the element in the second silicon-containing compound layer, wherein the first silicon-containing compound layer, the silicon layer and the second silicon-containing compound layer are adjacent the gate dielectric, and wherein the first and the second silicon-containing compound layers do not extend into the region directly underlying the gate dielectric; and a silicide region over and contacting the second silicon-containing compound layer, wherein the silicide region is spaced apart from the first silicon-containing compound layer and the silicon layer by the second silicon-containing compound layer.