A fresh approach has been applied to study the effect of ion energy on the anisotropy of polymer etching. A combination of microwave plasma excitation and RF biasing of an electrode on which etching substrates were placed, was used to independently control plasma density and the kinetic energy with which ions from the plasma strike the substrate. An empirical relationship is demonstrated which relates the rate of etching for polyimide films to the plasma density and the square root of the ion energy. Observations of lateral and vertical etch rates in a multilayer photoresist system have shown that in O2 plasmas there is a significant ion assisted component to the etching, and that this component is important even when ions have energies as low as 26eV. © 1986.