Spontaneous recovery of positive gate bias stressed power VDMOSFETs

Abstract

Spontaneous recovery of threshold voltage and channel carrier mobility in positive gate bias stressed power VDMOSFETs and the underlying changes in gate oxide-trapped charge and interface trap densities are presented and analysed. Electron tunneling from neutral oxide traps associated with trivalent silicon /spl equiv/Si/sub o//sup ./ defects into the oxide conduction band is proposed as the main mechanism responsible for stress-induced buildup of positive oxide-trapped charge. Subsequent hole tunneling from the charged oxide traps /spl equiv/Si/sub o//sup +/ to interface-trap precursors /spl equiv/Si/sub s/-H is proposed as the dominant mechanism responsible for the interface trap buildup. A chain of mechanisms related to a presence of hydrogen species is proposed in order to explain changes of oxide-trapped charge and interface trap densities during the spontaneous recovery. Interface trap /spl equiv/Si/sub s//sup ./ passivation due to their reaction with hydrogen atoms is proposed as a main mechanism responsible for a decrease of interface trap density. Hydrogen molecule cracking at charged oxide traps /spl equiv/Si/sub o//sup +/, which leads to their neutralization, is proposed as the dominant mechanism responsible for a decrease of oxide-trapped charge density.