Evaluation of plasma charging damage during polysilicon gate etching process in a decoupled plasma source reactor

Abstract

Charging induced damage of thin gate dielectric during polysilicon gate etching in a high density decoupled plasma source was investigated for 0.16 and 0.24 μm gates on 30 Å nitrided gate oxide. The undoped polysilicon gates were etched with a HBr/He/O2 based process recipe. The optimized process recipe resulted in vertical profiles (89°–90°) with microloading of <1°. No notching of the polysilicon or punch through of the thin gate oxide was observed. Gate leakage and breakdown voltage measurements after gate formation were made on metal-oxide-semiconductor capacitor structures with antenna ratios ranging from 100:1 to 1000:1. These measurements did not exhibit any damage to the thin gate dielectric. In addition, no significant change in the damage characteristics was observed over a wide process window around the optimized recipe, i.e., increased over etch (OE) time, increased source power, or reduced bias power in the OE step. A soft landing scheme was used for the etching of poly gates. This scheme provides vertical profiles without punch through and with minimum damage to the thin gate oxide and the substrate.