Surface processes in CF4/O2 reactive etching of silicon

Silicon surfaces etched in CF4/O2 plasma have been characterized with the use of in situ x-ray photoemisson spectroscopy. A SiFxOy layer on elemental silicon is formed under all conditions. For oxygen percentages greater than 5% in the feed gas, the oxygen content of the film and the film thickness increase, whereas the fluorine content of the film decreases. The Si etch rate decreases also and appears to be controlled primarily by the thickness of the SiFxOy layer, rather than by the F atom concentration in the gas phase, which increases up to 15% O2 addition.