Generation and relaxation phenomena of positive charge and interface trap in a metal-oxide-semiconductor structure

Abstract

Positive charge and interface trap generation during substrate hot-hole injection into the insulating layer of a metal-oxide-semiconductor (MOS) structure is investigated using p-channel MOS transistors with very thin oxide thicknesses in the range from 4.6 to 15 nm. Positive charge fluence in the oxide due to hole trapping is found to saturate for an injected hole density over 1016 cm−2. A model based on first-order trapping kinetics is presented to describe hole trapping phenomena including the dispersive nature of capture cross-section. A universal relationship between hole trapping and interface trap generation is observed experimentally, which implies direct involvement of holes in the formation of interface traps at the Si/SiO2 interface. A generation mechanism related with hole trapping in the oxide is discussed. Postinjection relaxation of the trapped holes showed strong dependence on both oxide field magnitude and polarity. Detrapping under positive gate voltage is consistent with the concept of direct tunneling discharge, while negative gate voltage relaxation occurs due to electron injection by Fowler–Nordheim mechanism. A new phenomena of time dependent annealing of interface traps has been observed after the end of hole injection, which contradicts the reports of time delayed interface trap generation.