A bias electrode was installed inside an etching chamber to investigate the effect of bias voltage on particle behavior. To detect flaked particles individually and to determine their trajectories, an in situ particle monitoring system which employs laser light scattering was employed. Consequently, it was found that particles were attracted when negative voltage was supplied to the bias electrode. However, particles were pushed toward the wafer when positive voltage was applied. It was thus clarified that the flaked particles have positive charges, and concluded that negative bias voltage can control their behavior and keep the wafer surface particle free, without serious affect on the etching process. (C) 2004 American Vacuum Society.