Threshold-voltage anomaly in sub-0.2 /spl mu/m DRAM buried-channel pFET devices

Measurements and simulation have been used to study threshold-voltage (V/sub t/) dependence on gate oxide thickness (t/sub ox/) for long-channel buried-channel (BC-) pFET devices in sub-0.2 /spl mu/m CMOS technologies. The combination of the dual gate oxide process using N/sub 2/ implantation to create the thinner gate oxide and well RTA results in the thinner t/sub ox/ devices having higher V/sub t/, contrary to expectation (V/sub t/-t/sub ox/ anomaly). Detailed analysis of doping profiles, depletion contours, and electric potential confirms this anomaly both in the enhancement and depletion modes of operation. These studies show that a balance of net doping between that near the surface and that around the BC-layer is a stringent requirement for the Vt control in BC-pFETS.