On the atomic scale defects involved in the negative bias temperature instability in 4H-SiC MOSFETs

Open Access
Author:
Follman, Jacob Jay
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 29, 2013
Committee Members:
  • Patrick M Lenahan, Thesis Advisor
Keywords:
  • NBTI
  • SiC
  • MOSFET
  • EPR
  • EDMR
Abstract:
We utilize electrically detected magnetic resonance (EDMR) to explore the effects of the negative bias temperature instability (NBTI) in 4H-SiC metal oxide semiconductor field effect transistors (MOSFETs). EDMR spectra due to oxygen vacancies, or E’ defect centers are generated in p-channel MOSFETs under elevated temperatures and modest negative gate bias stressing. The E’ concentration is shown to increase in response to increasing stress temperature. Our use of in-situ EDMR stress measurements suppresses recovery contamination and shows that the NBTI generated E’ centers disappear upon temperature stress removal. No such defect appears under the same stressing conditions for comparably-processed n-channel MOSFETs. In both types of devices, the silicon vacancy is the dominating central defect detected by EDMR, though this defect appears independent of and is unchanged by the NBTI stressing conditions. We conclude that E’ precursor sites at or very near the oxide/semiconductor interface in 4H-SiC pMOSFETs are activated under the negative bias temperature instability. Such defects may lead to large threshold voltage shifts and greatly reduced carrier mobility observed in the SiC/SiO2 system.