Physical Understanding of Strain-Induced Modulation of Gate Oxide Reliability in MOSFETs

We have systematically investigated the effects of strain on the gate oxide reliability, using biaxially strained Si MOSFETs, to elucidate their physical origins. It was found that the time-dependent dielectric breakdown reliability was significantly improved in strained Si nMOSFETs but was slightly degraded in strained Si pMOSFETs. These observations could be well explained by the strain-induced modulation of the gate current, resulting from band-structure modulation in the channels. It was also found that negative bias temperature instability was degraded in the strained Si pMOSFETs. This fact was attributable to the strain-induced enhancement of hole tunneling probability and hole wave function penetration into Si-H bonding states near the MOS interface, which could enhance Si-H bond breaking.