Quantum-mechanical simulation of counter doped channel metal-oxide-semiconductor field-effect transistors with single work function metal gate

The quantum-mechanical effects in counter doped n-channel metal-oxide-silicon field-effect transistors (MOSFETs) for metal gate complementary metal-oxide-silicon (CMOS) have been simulated using self-consistent calculations. The energy levels and fractional occupation of subbands, gate tunneling current and channel mobility in such metal gate MOSFETs have been investigated, comparing with those in n(+)-poly Si gate MOSFETs. The energy levels and fractional occupation for metal gate MOSFETs are fairly different from those for poly Si gate MOSFETs since the accumulation and inversion layers are formed on the respective surfaces by positive gate voltages. The tunneling current in metal gate MOSFETs is smaller than that in poly Si gate MOSFETs. In particular,at the gate voltages below I V, the current density is reduced by one order or above of magnitude. Moreover, the mobility in metal gate MOSFETs with lightly counter doped channel becomes much larger than that in poly Si gate MOSFETs because of the large suppression of ionized impurity scattering and surface roughness scattering.