Patent ID: 8836038

Claim:
A semiconductor structure comprising: a semiconductor substrate; a first MOS device of a first conductivity type, the first MOS device comprising: a first gate dielectric over the semiconductor substrate; a first metal-containing gate electrode layer over the first gate dielectric; a silicon-containing layer over and contacting the first metal-containing gate electrode layer; and a first contact etch stop layer having a first portion directly over the silicon-containing layer; and a second MOS device of a second conductivity type opposite the first conductivity type, the second MOS device comprising: a second gate dielectric over the semiconductor substrate; a second metal-containing gate electrode layer over the second gate dielectric, wherein a top surface of the first metal-containing gate electrode layer is lower than a top surface of the second metal-containing gate electrode layer; and a second contact etch stop layer having a second portion directly over the second metal-containing gate electrode layer, wherein no silicon-containing layer is disposed directly over the second metal-containing gate electrode layer and under the second contact etch stop layer.