The effect of sidewall roughness on the bottom etch profile and the etch rate of an SiO2 trench produced in a CF4 plasma were examined using a specially designed apparatus that involved a Faraday cage, which permits the observation of microfeatures on an enlarged scale under practical processing conditions. A microtrench was produced on the bottom of a trench-shaped structure with a low aspect ratio when its sidewalls were smooth because ions reflected from the sidewall enhanced the bottom etch rate near the sidewall. However, the microtrench was not produced in a trench-shaped structure with a high aspect ratio and smooth sidewalls because the effects of ions reflected from two sidewalls were overlapped, nor in step-shaped and trench-shaped structures with rough sidewalls because the contribution of reflected ions to the bottom etch rate was negligible. The overlap in ion reflection effects in a trench having a high aspect ratio and smooth sidewalls was responsible for the inverse reactive ion etching lag phenomenon observed in this study. (C) 2004 American Vacuum Society.