A comparison of hot-carrier degradation in tungsten polycide gate and poly gate p-MOSFETs

A study is made of hot-carrier immunity of tungsten polycide and of non-polycide, n/sup +/ poly gate, buried-channel p-MOSFETs, under conditions of maximum gate current injection. Increased hot-carrier degradation is observed for WSi/sub x/ p-MOSFETs under low drain voltage stress, where trap filling by injected electrons is the dominant degradation process. Stress-induced damage evaluated by gate-to-drain capacitance C/sub gd//sup s/ measurement shows increased susceptibility to electron trapping in the WSi/sub x/ device. F-induced oxide bulk defects introduced during polycidation may be responsible for the increased trapping observed. In addition, a significant decrease in electron detrapping rate is observed, which suggests a deeper energy distribution of F-related traps. The greater susceptibility to electron trapping, coupled with a decrease in electron detrapping rate, result in the reduction in DC hot-carrier lifetime over four orders of magnitude (based on /spl Delta/V/sub t/=50 mV criterion) under normal operating voltages. As hot-carrier effects in p-MOSFETs continue to be a concern for effective channel lengths less than 0.5 /spl mu/m, the reduced hot-carrier lifetime of WSi/sub x/ p-MOSFETs suggests that WF/sub 6/-based silicidation may not be appropriate for deep submicrometer CMOS devices.