Abstract
Si and SiO2 films have been etched using CF4 and H2 mixtures in a hollow cathode etching (HCE) reactor. We have measured etch rates and characterized the Si surfaces after HCE by x-ray photoemission spectroscopy (XPS). Addition of H2 to CF4 did not significantly enhance the etch rate ratio of SiO2 to Si. The fluorocarbon film, which is responsible for the achievement of SiO2/Si etch selectivity in reactive ion etching (RIE) reactors (1), has not been observed by XPS for Si surfaces etched in our HCE reactor at high RF power levels. This result is similar to that found in magnetron ion etching (MIE) at high power (2). C—C and C—H groups were the predominant species detected on Si surfaces etched in the HCE reactor; only small amounts of CFx were present. Low fluorination of the carbonaceous film is believed to be due to high dissociation rates of the parent molecules in both the HCE and the MIE reactors. The low fluorination of the carbonaceous deposits on SiO2 surfaces results in low etch rates for SiO2. When both carbon and fluorine arrive at the surface as in RIE, the oxygen in the SiO2 can form volatiles by reactions with carbon, while the Si can be removed by F atoms. When mostly carbon is deposited on the surface, as in HCE and MIE, the Si in the SiO2 is removed at a relatively slower rate. The thicknesses of the deposits on the Si surface were found to be smaller for the HCE reactor than for RIE reactor at high H2 percentages. Slow deposition of carbonaceous species on Si can account for the relatively high Si etch rates. The high Si etch rates and the effect of low fluorination of the carbonaceous deposits on SiO2 for CF4/H2 can account for the low etch rate ratios of SiO2 to Si in the HCE reactor. © 1989, The Electrochemical Society, Inc. All rights reserved.