Mechanism of reactive ion etching of 6H-SiC in CHF3/O2 gas mixtures

We report etch rates and surface composition after reactive ion etching (RIE) of carbon terminated 6H-SiC surfaces in CHF3/O-2 gas mixtures. The surface compositon is determined from fits to high resolution core level photoemission spectra and argon ion depth profiling. A maximum etch rate of 960 nm/min is obtained for similar to 60 vol% O-2 in CHF3 which drops by a factor of 70 towards the extremes of pure O-2 and CHF3. Up to 8 nm thick overlayers develop on the SiC surface during the etch process They consist mainly of amorphous carbon with a CF1.6 layer on top on the CHF3 rich side and of SiO2 on the O-2 rich side of the CHF3/O-2 gas mixture and their thickness decreases monotonically to a fraction of a nm as the corresponding gas component is reduced to zero. A model is developed that takes the formation of these adlayers as well as their influence on the transport of radicals to the buried SiC surface into account. It describes the variation in etch rate and overlayer thickness with gas composition quantitatively.