Impact of backside interface on Hot Carriers degradation of thin film FDSOI Nmosfets

Abstract

Based on simulation results, we show that defects at the Si/Box interface of FDSOI transistors can have a detrimental impact on reliability. In particular, attention is paid to Hot Carriers degradations (HC) on ultra thin film FDSOI NMOSFETs for which defects can be created very close to the back gate interface. A new technique based on capacitance measurements is proposed to localize HC degradation at front gate and/or back gate interface on FDSOI transistors. Thanks to this method, it is shown that, similarly to bulk technologies, only the front gate interface is degraded during a classical HC stress. Finally, despite the presence of an additional Si/BOx interface, FDSOI NMOSFETs down to 30nm gate length exhibit HC lifetimes over 10 years, even when a back bias is applied.