The effects of adding H-2 or CBrF3 to Cl-2 plasma 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 pure Cl-2 plasma at the pressure of 12 Pa are vertical or sloped depending on whether a radio frequency (rf) power of 600 W (0.77 W/cm(2)) or 700 W (0.9 W/cm(2)) is applied. By increasing the content of H-2, the angle of the sidewall taper of the pattern etched at 600 W rf power reaches 70 degrees Adding CBrF3 makes it possible to adjust the slope of the sidewall over a range from 77 degrees to 65 degrees at a rf power of 700 W. These observed results are attributed to plasma polymerization.