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Silicon Dry Etching in Hydrogen Iodide Plasmas: Surface Diagnostics and Technological Applications

We have investigated hydrogen iodide (HI) as an alternative to conventional chlorine or bromine chemistry for dry etching. Plasma exposed Si surfaces show damage, as revealed by photoluminescence studies. These defects can be annealed out by thermal treatment at 550° C. We have developed an anisotropic polysilicon gate etch process for 0.35 µ m MOS technology based on iodine chemistry. The selectivity between polysilicon and oxide is determined as a function of various process parameters. Decreasing the rf source power from 350 to 100 W increases the selectivity between polysilicon and SiO2 from approx. 30:1 to 180:1. Profiles with a degree of anisotropy close to unity can be obtained without trenching or other undesirable anomalies. Iodine-based plasmas are characterized by very low self-biased voltages, typically less than 70 V.