Surface mechanisms in O2 and SF6 microwave plasma etching of polymers

Photoresist etching mechanisms in O2 abd SF6 microwave plasmas are investigated using x-ray photoelectron spectroscopy (XPS) and etch rate measurements. Experiments are performed in a microwave multipolar plasma using an electron cyclotron resonance at 2.45 GHz and independent rf biasing at 13.56 MHz. The photoresist etch rates are studied as a function of the parameters of the plasma polymer interaction. As in an O2 plasma, the etch rate in SF6 exhibits a two-step evolution with ion energy as well as a monolayerlike adsorption of atomic fluorine on photoresist. The relationship between the surface mechanisms deduced from the etch kinetics and the surface compositions analyzed by XPS is explored. The effect of reactive species concentration, intensity of ion bombardment, and surface temperature on etching and/or degradation of the photoresist is investigated. In particular, the phenomenon of resist damage, described as a graphitization of the polymer layer, is shown to appear when the mechanical effects of ion bombardment become significant with respect to the chemical effects.