Mobility enhancement on nano-strained NMOSFET with epitaxial silicon buffer layers

SiGe deposition as a channel layer to promote the channel mobility is a promising way in the development of nano-level MOSFET (metal-oxide-semiconductor field-effect transistor). However, the thermal or mechanical stress between strained SiGe layer and crystalline wafer surface is increased more and easy to generate the dislocation defects, inversely reducing the channel mobility performance. Using the Si buffer layer is an effective method to release these stresses, but the optimal thickness of this buffer layer must be controlled well, otherwise the Ge atom diffuses more into this layer and deteriorates the desired function of depositing SiGe as a channel layer at 90-nm-node process or below.