In order to investigate the mechanism of etching in low pressure radio-frequency (rf) plasmas, we adopt a two-dimensional Monte-Carlo (MC) cellular method to simulate the profile evolution, in which the ion reflection, the ion angular distribution (IAD) etc. are considered. It is found that the phenomenon of microtrenching results from the reflection of particles on the sidewall and the IAD is responsible for round corners at the bottom of the trench. The deeper the trench is, the more easily microtrenching or notching appear. In addition, the neutral particles can destroy the anisotropic etching of the trench and lead to bowling. On the other hand, by means of solving the Laplace equation near and in the trench with an iterative procedure, we obtain a stable or periodic stable electric field biased by a dc or rf source, in which the charging effect on the photoresist sidewall of the trench is considered. It is observed that both the dc and rf biases applied to the substrate can influence the profiles of etching, and the better etching profiles on the sidewall of the trench can be obtained with the rf bias than those with the dc bias. (C) 2011 Elsevier B. V. All rights reserved.