Mobility enhancement in local strain channel nMOSFETs by stacked a-Si/poly-Si gate and capping nitride

A local strained channel nMOSFET has been fabricated by a stress control technique utilizing a stacked a-Si/poly-Si gate and a SiN capping layer. It is found that the transconductance (G/sub M/) of nMOSFETs increases as the thickness of a-Si is increased. We also found that the G/sub M/ of devices with the SiN capping layer exhibits a 17% increase compared to that of its counterparts. The stacked gate a-Si/poly-Si with the capping layer can improve the G/sub M/ further to 29% more than the single-poly-Si gate structure without SiN capping layer.