Strain induced changes in the gate leakage current of n-channel metal-oxide-semiconductor field-effect transistors

Abstract

Changes in the gate direct tunneling current in the accumulation layer and in the inversion layer are measured for tensile strained n-channel metal-oxide-semiconductor-field-effect-transistors (MOSFETs) with a polysilicon gate and a TaN gate on (100) silicon wafers. The observed decrease of the polysilicon gate tunneling current in the inversion layer and the accumulation layer for uniaxial tensile stress primarily results from electron repopulation into the Δ2 valley with a larger out-of-plane effective conductivity mass. However, due to weak confinement and the Fermi energy approaching the conduction band edge in the accumulation layer, the normalized leakage current change is higher in the accumulation layer than in the inversion layer. In contrast with polysilicon gate MOSFETs, the direct tunneling current in metal gate MOSFETs increases with uniaxial tensile stress in the accumulation layer, which may be understood from the C-V measurement of the strain-induced TaN work function shift. A self-consistent solution to Poisson’s and Schrödinger’s equations, considering the strain Hamiltonian combined with the transfer matrix method, is used for modeling the electron tunneling process.