Abrupt reduction in poly-Si etch rate in HBr/O₂ plasma

The effect of oxygen on polycrystalline-Si (poly-Si) and SiO₂ etching in hydrogen bromide (HBr) reactive ion etching plasmas has been studied by measuring etch rates and using x-ray photoelectron spectroscopy (XPS) to study compositional changes in the surface layer. The etch rate of the poly-Si increases dramatically from 30 to 235 nm/min as the O₂ concentration increases from 0% to 25%, whereas the SiO₂ etch rate gradually decreases from 3 to 1 nm/min. Above 30% O₂ in HBr, the poly-Si etch rate abruptly decreases by a factor of 16 compared with that at 25%. From XPS analysis, it is found that the abrupt decrease of the poly-Si etch rate at O₂ concentrations of more than 30% is closely related with the composition and thickness of an SiBr_xO_y layer formed during the HBr/O₂ plasma exposure. The SiBr_xO_y layer has a composition of nearly SiO₂. Br ions cannot permeate the SiBr_xO_y layer formed in plasmas containing 30% O₂ in HBr (or greater), and therefore, the poly-Si etch terminates. © 1998 American Vacuum Society.