High performance cmos device design

Abstract

A semiconductor device includes a gate, which comprises a gate electrode and a gate dielectric underlying the gate electrode, a spacer formed on a sidewall of the gate electrode and the gate dielectric, a buffer layer having a first portion underlying the gate dielectric and the spacer and a second portion adjacent the spacer wherein the top surface of the second portion of the buffer layer is recessed below the top surface of the first portion of the buffer layer, and a source/drain region substantially aligned with the spacer. The buffer layer preferably has a greater lattice constant than an underlying semiconductor substrate. The semiconductor device may further include a semiconductor-capping layer between the buffer layer and the gate dielectric, wherein the semiconductor-capping layer has a smaller lattice constant than the buffer layer.