Effect of an Ultrathin SiN Cap Layer on the Bias Temperature Instability in Metal–Oxide–Semiconductor Field-Effect Transistors with HfSiON Gate Stacks

Abstract

The negative-bias temperature instability (NBTI) and positive-bias temperature instability (PBTI) of HfSiON/SiO2 metal–oxide–semiconductor field-effect transistors (MOSFETs) with and without an ultrathin SiN cap layer were investigated. For the PBTI of n-channel MOSFETs, the dominant degradation mechanism is the electron tunneling from the Si channel and electron trapping in the pre-existing traps in HfSiON. The SiN cap layer does not make a significant difference in PBTI. For the NBTI of p-channel MOSFETs, on the other hand, both the electron trapping in HfSiON and the dissociation of Si–H bonds at the SiO2/channel-Si interface (i.e., the interface trap generation) play a role and the SiN cap layer makes a significant difference in NBTI: the dominant degradation mechanism for the devices without the SiN cap layer is the electron trapping in HfSiON, whereas that for the devices with the SiN cap layer is the interface trap generation. This indicates that the interfacial SiN cap layer can effectively suppress the electron tunneling from the polycrystalline silicon (polySi) gate to HfSiON under the NBT stress.