This article discusses the etching and selectivity of 3C-SiC films grown on Si substrates using CHF3/O-2 and CHF3/O-2/He plasmas at a pressure of 1.75 Torr. The addition of helium increases the etch rates of SiC and Si for most CHF3, and O-2 concentrations. For both CHF3/O-2 and CHF3/O-2/He plasmas with O-2 concentrations up to 85%, the SiC etch rate increases monotonically and the Si etch rate decreases monotonically with increased percentages of O-2. At an O-2 concentration of 80%, the addition of helium to the CHF3/O-2 plasma results in an etch rate of 1267 Angstrom/min, which is the highest reported for etching 3C-SiC using a CHF3-based plasma in a conventional, parallel plate plasma reactor. The addition of helium also increases the etch anisotropy. This study also investigated aluminum micromasking of SiC etch fields and finds the primary source to be sputtered aluminum from the etch mask.