Improvement of negative-bias-temperature instability in SiN-capped p-channel metal-oxide-semiconductor field-effect transistors using ultrathin HfO2 buffer layer

Abstract

Characteristics of p-channel SiN-capped metal-oxide-semiconductor field-effect transistors (PMOSFETs) with a thin HfO2 buffer layer were investigated. The compressive strain in the channel was deliberately induced in this study by a SiN capping layer over the gate using plasma-enhanced chemical vapor deposition (PECVD). Although a compressive SiN capping effectively boosts the drive current of PMOSFET devices, its presence also worsens the negative bias temperature instability (NBTI) characteristics due to the high hydrogen content in the SiN layer, which could diffuse into the channel region during the deposition process. To address this issue, the insertion of a 3 nm thick HfO2 buffer layer between the gate and SiN capping is proposed and demonstrated to improve NBTI reliability without sacrificing the device performance enhancement. (c) 2007 The Electrochemical Society.