V/sub ox//E/sub ox/-driven breakdown of ultra-thin SiON gate dielectric in p+gate-pMOSFET under low stress voltage of inversion mode

We have studied the breakdown mechanism of ultra-thin SiON gate dielectrics in p+gate-pMOSFETs. A systematic study with varying gate doping concentrations has revealed that, in the case of p+gate-pMOSFETs in inversion mode, gate dielectric breakdown under low stress voltage is driven by oxide voltage (V/sub ox/) or oxide field (E/sub ox/), while the breakdown under higher stress voltage is driven by gate voltage (V/sub g/). The V/sub ox//E/sub ox/-driven breakdown which emerges under low stress voltage is quite important to the reliability of low-voltage CMOS. By studying the mechanism of the breakdown, it has been clarified that the breakdown is not induced by electron current. The concept that the breakdown is due to the same mechanism as NBTI, namely the interfacial hydrogen release driven by E/sub ox/, has been shown to be possible. However, direct tunneling of holes driven by V/sub ox/ has also been found to be a possible driving force of the breakdown. Although a decisive conclusion concerning the mechanism issue has not yet been obtained, the key factor that governs the breakdown has been shown to be V/sub ox/ or E/sub ox/.