The two-dimensional modeling of the etching of silicon in CF4 + O-2 plasma is considered. The profiles of etched trenches at real dimensions are calculated as a function of mask dimensions, concentrations of chemically active and non-active plasma components and ion bombardment parameters. The chemical composition of the CF4 + O-2 plasma is calculated, and the one-dimensional plasmochernical etching (PCE) of silicon in the plasma is investigated to achieve the goal. It was found that for O-2 content in feed greater than 20%, the etching anisotropy increases, whereas the aspect ratio approaches a steady-state value. The etching anisotropy is achieved due to the fort-nation of SiO2, on the sidewalls and the decrease of concentration of fluorine atoms in the plasma. (C) 2002 Elsevier Science B.V. All rights reserved.d