UTILIZATION OF PLASMA HYDROGENATION IN STACKED SRAMS WITH POLY-SI PMOSFETS AND BULK-SI NMOSFETS

Poly-Si PMOSFET's are being utilized with bulk-Si NMOSFET's in stacked SRAM cells. Results regarding utilization of a plasma hydrogenation step in a stacked SRAM process sequence are reported for the first time. It is found that poly-Si PMOSFET's exhibit an increase in ON/OFF current ratio of four orders of magnitude. Bulk-Si NMOSFET's subjected to the same hydrogenation process exhibit no significant decrease in device lifetime or significant degradation in I-V characteristics compared to NMOSFET's which were not subjected to the plasma hydrogenation process. These results thus indicate that plasma hydrogenation can successfully be utilized to obtain improved performance stacked SRAM's.