A COMPARISON OF HOT-CARRIER DEGRADATION IN TUNGSTEN POLYCIDE GATE ANDPOLY GATE P-MOSFETS

A study is made of hot-carrier immunity of tungsten polycide and of no n-polycide, n(+) poly gate, buried-channel p-MOSFET's, under condition s of maximum gate current injection, Increased hot-carrier degradation is observed for WSI, p-MOSFET's under low drain voltage stress, where trap filling by injected electrons is the dominant degradation proces s, Stress-induced damage evaluated by gate-to-drain capacitance C-gd(s ) measurement shows increased susceptibility to electron trapping in t he WSix device, F-induced oxide bulk defects introduced during polycid ation may be responsible for the increased trapping observed. In addit ion, a significant decrease in electron detrapping rate is observed, w hich suggests a deeper energy distribution of F-related traps. The gre ater susceptibility to electron trapping, coupled with a decrease in e lectron detrapping rate, result in the reduction in de hot-carrier lif etime over four orders of magnitude (based on Delta V-t = 50 mV criter ion) under normal operating voltages, As hot-carrier effects in p-MOSF ET's continue to be a concern for effective channel lengths less than 0.5 mu m, the reduced hot-carrier lifetime of WSix p-MOSFET's suggests that WF6-based silicidation may not be appropriate for deep submicrom eter CMOS devices.