The etching of polymers in oxygen-based plasmas: A parametric study

Abstract

A parametric study of the etching of polymers has been performed in a 2.45-GHz microwave multipolar plasma using an electron-cyclotron-resonance excitation and an independent 13.56-MHz rf biasing. The etch rates achieved in N2O and N2/O2 discharges are measured as a function of different plasma parameters, i.e., the ion current density bombarding the wafer surface, the ion energy, and the relative atomic oxygen concentration as estimated by actinometry. In both types of plasmas, the etch rate evolutions with ion energy exhibit a two-step variation corresponding first to ion-induced adatom displacements on the polymer surface and second, above a threshold energy, to the rising of sputtering. Under given ion bombardment conditions the polymer etch rate, unchanged by the presence of molecular oxygen, appears to be only controlled by the atomic oxygen concentration in the plasma. The etching kinetics, which first increases proportionally to ion current density and atomic oxygen concentration before reaching saturation, clearly indicates a monolayerlike adsorption of oxygen on polymers. With this hypothesis, the etching behavior can be fully explained by a model recently proposed for plasma etching.