The importance of free radical recombination reactions of F in CF4/O2 plasma etching of Si is explored in a combined experimental and modeling study of a single wafer etcher. The F atom concentration profiles in the reactor, as well as the silicon etch rate profiles, are strongly influenced by the recombination reactions. The surface recombination reaction is more important than the gas phase recombination reactions in determining overall system behavior. The effects of the homogeneous as well as heterogeneous recombination reaction diminishes with increasing flow rate. This is due to combined residence time and transport effects. © 1990, American Vacuum Society. All rights reserved.