Plasma etching processes often roughen the feature sidewalls, leading to the formation of anisotropic striations. The primary cause of sidewall roughening is the templating of mask roughness into the underlying film. Specifically, the inherent roughening of photoresist provides the mask for templating effect. To fully understand the sidewall roughness evolution, it is critical to characterize the inherent roughening of photoresist as well as other materials, such as porous low-k film. A polymerization-induced micromasking mechanism was proposed to explain the surface roughening of porous low-k films. Porous structure in the substrate plays a critical role in the film roughening evolution. This effect can be understood using the concept of pore filling with polymeric deposition that etches more slowly under fluorocarbon plasma exposure. Later on, the polymer forms micromasks that induce roughening. Although scaled with the ion bombardment energy, the roughness level of porous low-k film etched in C2F6 plasma is mainly related to the film thickness removed; no similar trend was observed on non-porous OSG films under same etching conditions. Fluorocarbon plasmas with different polymerization capabilities such as 20% C4F8/ 80% Ar, were used to explore the polymerization effects. Additionally, the correlation between polymer deposition and porosity/pore size distribution of low-k films was investigated. The roughening of photoresist blank films can also be explained based upon the mechanism proposed above. It was found that photoresist roughening was influenced by etching chemistries and some other factors. In particular, the inhomogeneity introduced during blank film development process formed some equivalent "pores" at near surface region. These "pores" had significant impact on the roughness evolution during etching in fluorocarbon plasmas.