In this paper, a 0-dimensional model for the understanding of dry etching characteristics in silicon oxide and nitride materials is reported. The model is applied to analyze the etching performances in a design of experiments where gas mixtures are varied in the fluorocarbon chemistry typical of the “protected sidewall” regime. The modeling analysis of flat sample etching allows for an accurate tuning of the selectivity's behavior, and can be generalized to deal with patterned samples. In particular, we apply a phenomenological technique to transform the equipment parameters in the microscopic quantities ruling the reagent-surface interactions. The correct prediction of the etch rate trends in flat samples and the sensibility to the different etching mechanisms for the nitride case demonstrate the reliability of the proposed approach.