Parameters which influence the etching of polyimide (PI) downstream of an O2–CF4–Ar microwave (MW) plasma were studied. Of particular importance is the influence of the ratio of atomic number densities O/F in the plasma and the gas flow velocity, which caused an almost linear increase in the etch rate within the investigated limits of the experiment. No measurable etching of PI was found downstream of an O2–Ar plasma, although the presence of oxygen atoms in the vicinity of the substrate was verified by the chemiluminescent reaction with NO. Similar to previously reported radio frequency plasma studies, a fluorinated layer at the surface of (PI) was formed by exposure of the substrate downstream of a fluorine‐rich O2–CF4–Ar MW plasma. Changing the plasma composition to the optimum etching conditions (an oxygen‐rich plasma of about 20% CF4) removed the fluorinated layer after a period of time. Etching then proceeded with an oxygenated layer at the surface. The reported experiments confirmed that the formation of a fluorinated layer, the removal of this layer, and the formation of an oxygenated one was caused only by the interaction of neutrals, without the influence of ion bombardment.