A study on the V/sub th/ shift of HfAlOx MISFETs with n+/p+ poly-Si and TiN gate electrodes fabricated by replacement gate process

The V/sub th/ shift of a poly-Si/high-k MISFET has been reported. The observed V/sub t/h of p/sup +/ poly-Si/HfAlO/sub x/ or HfSiO/sub x/ is much higher than that of the p/sup +/ poly/SiON MISFET. The controlled V/sub th/ of the PMISFET is strongly required for the application of high-k insulators. In this study, we fabricated HfAlO/sub x/ MISFETs with n/sup +//p/sup +/ poly-Si and TiN gate electrodes by using the same "replacement gate" process. We found that the difference of V/sub fb/ between n/sup +/ poly-Si-/HfAlOx and p/sup +/ poly-Si/HfAlO/sub x/ systems is independent of channel types and much smaller than 1 V i.e. the theoretical difference between the work function of n/sup +/ and p/sup +/ Si. On the other hand, the TiN/HfAlO/sub x/ system shows the appropriate V/sub fb/ expected from work function.