For quartermicron lithography, fine pattern etching of bilayer resist was investigated using O-2/N-2 supermagnetron plasma. The maximum etch rate was obtained at a radio frequency (rf) phase difference of 150 degrees-180 degrees which was observed between two rf powers of the same frequency supplied to two parallel electrodes. The side etchings of resist walls were reduced by lowering the electrode (wafer) temperature to - 30 degrees C. By the increment of N-2 concentration from 0% to 60%, the etch rate decreased little, and the side etchings of resist walls became only +/-0.015 mu m at a self-bias voltage V-dc of - 140 to - 180 V. Microloading effect was greatly improved by lowering a wafer temperature to - 30 degrees C and by increasing V-dc to - 180 V.