Roughness evolution in polyimide films during plasma etching

Abstract

We report an experimental study on the evolution of etch front roughness in fluorinated polyimide films in oxygen based plasmas. For standard low-pressure (40 mT) etching conditions, the root-mean-square roughness, w, of the polymer surface increases with the amount of material etched, d, as w=0.0265(d−116)β with β=1, independent of etch rate, rf power, and gas composition. The etched surfaces can be described by the statistics of self-affine surfaces with scaling exponent, α=0.6±0.1 and lateral correlation length, ξ, of ∼0.3 μm. A dramatic reduction in roughness is observed under higher pressure etching conditions of 1000–2000 mT.