Substrate Trenching Mechanism during Plasma and Magnetically Enhanced Polysilicon Etching

Abstract

Plasma and magnetically enhanced reactive ion etching processes with chlorine gas have been developed for subhalf micron polysilicon gate electrode etching (1). In this paper, gate oxide trenching during polysilicon gate etching using chlorine‐based reactive ion etching (RIE) and magnetically enhanced reactive ion etching (MERIE) processes is studied in detail. The trenching mechanism was found to be a direct result of off‐angle ion bombardment and reflection from the partially etched polysilicon sidewall during plasma etching. The off‐angle ion bombardment is caused by the elastic collision between ions and neutrals as ions move across the plasma sheath. Monte Carlo simulation confirms the angular distribution of ions under most plasma processing conditions. A two‐step MERIE process, first with high etch rate and high anisotropy and second with high selectivity to the gate oxide, with low ion energy bombardment is also developed to minimize the trenching effect during polysilicon‐gate etching.