Impact of crystalline phase of Ni-FUSI gate electrode on bias temperature instability and gate dielectric breakdown of HfSiON MOSFETs

We investigated the influences of gate metals (n(+)/P+ poly-Si, Ni silicide (NiSi), Ni3Si) on the time dependent dielectric breakdown (TDDB) reliability and negative/positive bias temperature instability (NBTI/PBTI) of phase-controlled Ni-full-silicide (Ni-FUSI)/HfSiON/SiO2 FETs. The TDDB reliability of NiSi-electrode n-FETs was comparable to that of n(+)-poly-Si-electrode n-FETs. However, further Ni enriching of the electrode to Ni3Si degraded the reliability. A degradation of the base SiO2 layer seems to have been responsible for this. A higher compressive strain was observed for the Ni3Si sample, which may have caused the degradation of the bottom SiO2. In contrast, the TDDB reliability of p-FETs improved much by using Ni3Si. We attribute this improvement to the lower cathode energy and/or the absence of boron in the gate electrode. The PBTI of the n-FETs was negligible and was not degraded by Ni enrichment of the gate electrode and additional annealing, suggesting that HfSiON was stable against the Ni-FUSI process. The threshold voltage (V-T) shift in NBTI of p-FETs did not depend much on the gate materials. The major component of the V-T shift in NBTI, however, was changed by Ni enriching from the generation of interface traps to the trapping of holes by the HfSiON bulk.