Control of behavior of particles flaked off an anode in plasma etch-back equipment by bias electrode

An in situ particle-monitoring system-which uses laser light scattering to detect "flaked particles" individually and determines their trajectories-was developed and installed in a tungsten RF plasma etch-back machine. It was found that the flaked particles have a positive charge. We installed a bias electrode inside the etching chamber in order to investigate the effect of a bias voltage on particle behavior. Consequently, it was shown that the particles are captured when the supplied voltage on the bias electrode is less than -100 V. On the other hand, a lot of particles are produced and pushed toward the wafer when the voltage is more than -50 V. It is therefore concluded that the bias electrode can control the behavior of the flaked particles and keep the chamber particle free.