Fluorocarbon polymer formation, characterization, and reduction in polycrystalline-silicon etching with CF4-added plasma

Addition of CF4 into HBr-based plasma for polycrystalline-silicon gate etch ing reduces the deposition of an etch byproduct, silicon oxide, onto the ch amber wall but tends to generate organic polymer. In this work, a detailed study has been carried out to analyze the mechanism of polymerization and t o characterize the polymer composition and quantity. The study has shown th at the polymer formation is due to the F-radical depletion by H atoms disso ciated from HBr. The composition of the polymer changes significantly with CF4 concentration in the gas feed, and the polymer deposition rate depends on CF4% and other process conditions such as source power, bias power, and pressure. Surface temperature also affects the polymer deposition rate. Add ing O-2 into the plasma can clean the organic polymer, but the O-2 amount h as to be well controlled in order to prevent the formation of silicon oxide . Based on a series of tests to evaluate polymer deposition and oxide clean ing with O-2 addition, an optimized process regime in terms of O-2-to-CF4 r atio has been identified to simultaneously suppress the polymer and oxide d eposition so that the etch process becomes self-cleaning. (C) 2001 American Vacuum Society.