Electrical characteristics of boron-implanted n-channel MOS transistors

Abstract Back-gate-bias V BG dependence of threshold voltage V T and gate-bias V G dependence of “gain” term β (and effective mobility μ eff ) of 50-keV-boron-implanted n -channel MOS transistors are described as functions of implant dose. In low field region, e.g. forward-biased V BG , the slopes of √[−( φ sub + V BG )] vs V T characteristics depend on the implant dose, while under high reverse bias, the slopes are constant and determined by the unimplanted substrate impurity concentration. Corresponding to this, the V G vs β ( μ eff ) characteristics indicate strong dose dependence and reduction of β ( μ eff ) in low field, while in high field the reduction of β ( μ eff ) is observed but not so significant. The effect is clear in the case of a deeply implanted layer or in case of a large ratio of effective channel length to width, as predicted by transistor equations.