Physical Understanding of Strain Effects on Gate Oxide Reliability of MOSFETs

The strain effects on TDDB and NBTI are systematically investigated using biaxially strained Si MOSFETs and their physical origins are examined. It is found that TDDB reliability of nMOS is significantly improved in strained-Si MOSFETs, while that of pMOS is slightly degraded. These dependences are well explained by the strain-induced modulation of gate current. It is also found that NBTI reliability is degraded by applying the biaxial tensile strain. This could be due to strain-induced enhancement of tunneling probability of holes into Si-H bonding states near the MOS interface.