Mechanism of High Selectivity and Impurity Effects in HBr RIE: In-Situ Surface Analysis

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Abstract
The brominated surface layer of SiO2 was studied after HBr reactive ion etching (RIE) with in-situ X-ray photoelectron spectroscopy (XPS). Bromine was observed, but neither the Si-Si nor the Si-Br x bond was spectrally detected. Most of the bromine on the SiO2 surface desorbed after atmospheric exposure. Oxygen was depleted by both HBr RIE and rare gas sputtering, and the XPS peak was broadened by sputtering. Carbon addition enhanced the oxygen depletion and the peak broadening. Results indicate that the conventional “chemical sputtering” does not occur in the HBr RIE of SiO2, but rather oxygen extraction by ion bombardment or preferential sputtering initiates the etching reaction. After the extraction, bromine reacts with silicon within the same collision cascade, and prevents the Si-O recombination, which is observed as the peak broadening. Carbon enhances the oxygen extraction.