The effects of addingH2orCBrF3toCl2plasma to control the pattern profile in polysilicon etching are studied using a magnetron reactive ion etching system. It is found that the sidewalls of patterns etched with pureCl2plasma at the pressure of 12 Pa are vertical or sloped depending on whether a radio frequency (rf) power of 600 W (0.77W/cm2) or 700 W (0.9W/cm2) is applied. By increasing the content ofH2, the angle of the sidewall taper of the pattern etched at 600 W rf power reaches 70°. AddingCBrF3makes it possible to adjust the slope of the sidewall over a range from 77° to 65° at a rf power of 700 W. These observed results are attributed to plasma polymerization.