Increasing Mobility in 4H-SiC MOSFETs with Deposited Oxide by <i>In-Situ</i> Nitridation of SiC Surface

Abstract

We present the improvement of SiO2/4H-SiC interface quality and high field-effect (FE) mobility (µFE) in 4H-SiC MOSFETs. This is achieved by introducing a nitrous oxide (N2O) plasma in-situ pre-treatment before gate stack formation using plasma enhanced chemical vapour deposition (PECVD) oxide followed by a post deposition anneal (PDA) in diluted N2O for times ranging from 30 to 120 minutes thereby creating an ultra-thin thermally grown SiO2 layer at the SiO2/4H-SiC interface. MOS capacitors with SiO2 deposited on in-situ pre-treated SiC surfaces had a lower density of interface traps (DIT) for all PDA durations, compared with devices having untreated PECVD oxides or control devices with 30 nm thermally grown oxide. After PDA for 90 minutes, a minimum DIT value of 1.2×1011 cm-2·eV-1 was measured. A peak µFE value reaching 94 cm2/(V·s) was measured in n-channel planar MOSFETs fabricated with PECVD oxide on in-situ pre-treated devices, which significantly exceeds a maximum µFE of 6 cm2/(V·s) in control devices.