A single-trap study of PBTI in SiON nMOS transistors: Similarities and differences to the NBTI/pMOS case

To identify the physical mechanism behind the recoverable component of the bias temperature instability (BTI), the time dependent defect spectroscopy (TDDS) has been recently proposed and used extensively. The TDDS makes use of the fact that in nano-scale devices the recovery proceeds in discrete steps. By analyzing the statistical properties of the steps, valuable information about the BTI degradation mechanisms can be obtained. So far, most single-defect studies have focused on NBTI in SiON devices as well as PBTI in high-k gate stacks. In order to deepen our understanding of the traps responsible for this detrimental phenomenon, we focus here on PBTI in SiON nMOSFETs, which have not been studied in great detail so far. From large-area devices it is known that PBTI/nMOS is about one order of magnitude lower than NBTI/pMOS. Unlike pMOSFETs, where hole trapping is responsible for BTI, in the case of nMOSFETs electron traps have to be considered.We show here that defects causing PBTI in nMOSFETs have a similar individual trapping behavior and dependence on the bias and temperature as observed for hole traps in previous NBTI/pMOS studies. Interestingly, like in pMOSFETs, we observe switching and fixed charge traps, which allows us to adapt our previously suggested model for hole capture to electron capture in nMOSFETs.