Influence of Interface Roughness on Electrical Properties of pMOSFETs with a Si/Si1- xGex Channel

Abstract

The effect of epitaxial growth induced surface roughness on the electrical properties of Si/Si1-xGex channel pMOSFETs was investigated. Grown by chemical vapour deposition for selective epitaxy, the surface of the channel region was considerably rougher for the channel structures with a buried Si1-xGex layer with x = 0.16-0.20 than for those with only Si. Although the increased surface roughness, determined by means of atomic force microscopy, resulted in a doubled interface charge density, the density remained low at the mid-1010 cm-2 eV-1 level. Furthermore, identical transconductance values were found for the MOSFETs with and without the Si1-xGex layer. Since the inversion charge was confined predominantly within the surface Si layer, the surface roughness apparently had little effect on the transconductance. However, the subthreshold slope was found to increase from 78 mV/decade for the Si-only channel MOSFET to 105 mV/decade for the Si/Si1-xGex channel MOSFETs.