Observation of energetic particles bombarding substrate in RF sputtering by time-of-flight method

A time-of-flight probe, originally developed for DC sputtering, is modified to permit its application to RF sputtering. This is achieved by minimizing the RF-induced noise to increase the S/N ratio. The improved probe can serve to observe high-speed particles involved in RF sputtering. The report presents some observations of high-speed particles involved in RF sputtering and compares them with those for DC sputtering. Investigations show that the time-of-flight method can be useful for in-situ observation of high-speed particles in RF sputtering as well as in DC sputtering. Information on the conditions of target surface is obtained from observations of high-speed particles. Furthermore, positive ions hitting the substrate can be observed at low gas pressure, permitting measurement of plasma potential. Investigations also indicate that RF planar magnetron sputtering is comparable with DC planar magnetron sputtering with respect to the effect of high-speed particles on resultant ZnO film and that a greater number of O2+ ions hit the ZnO target in the case of RF sputtering. (N.K.)