Method of forming CMOS transistor having a deep sub-micron mid-gap metal gate

摘要

A CMOS transistor is formed on a single crystal silicon substrate. Active regions are formed on the substrate, including an nMOST active region and a pMOST active region. An epitaxial layer of undoped silicon is formed over the active regions. Out-diffusion from the underlying active regions produces dopant densities within the epitaxial layer one, or more, orders of magnitude lower than dopant densities within the underlying active regions. In a preferred embodiment, the epitaxial layer is counter doped by implanting ions of the opposite type to those within the underlying active region. Counter doping further reduces the dopant density, to reduce the threshold voltage further.