ELECTRICAL CHARACTERISATION OF MOS GATE OXIDE

Abstract

The characteristics of non-polycided (poly-gate) and polycided (WSix-gate) metal-oxide-semiconductor (MOS) capacitors are studied to find out the effects of polycidation process on the oxide quality. Results of constant current stress show that tungsten silicidation greatly improves the immunity of the MOS gate oxide to Fowler-Nordheim stress-induced charge generation and trapping. The silicidation process appears to have hardened the oxide to new trap creation. Strain relaxation and new oxide growth ≈ 10 Å due to fluorine interaction are believed to produce a superior Si/Si02 interface. The formation of more stable Si-F bonds, which replace Si-H bonds, could be one of the reasons for the improved interface. High-frequency Capcitance Voltage (CV) and Quasi-Static CV curves reveal a dependence on the gate bias ramp rates. This observation is due to reduced recombination rate of minority carriers in the shallow well. The effect of measurement on CV curves after stress can also be substantial. The electron trap capture cross section near the cathode of WSix-gate capacitors after stressing at 1 µA cm-2 for 260 000 s is approximately 10-18 cm2. The effective electron trap density is approximately 2.6 x 1011 cm-2 . These values are independent of substrate type. Results of constant current stress on NO-nitrided oxide grown under 3 different rapid thermal processing (RTP) conditions, indicate stress-induced leakage current (SILC) in NO-nitrided oxide to be higher than that of non-nitrided oxide. This suggests that NO-nitrided oxides may not be used as a substitute for Si02 when gate oxide thickness is less than 7 nm.