Studies of mid-frequency pulsed dc biasing

The application of mid-frequency (100-350 kHz) pulsed dc power at the subst rate is a recent development in the magnetron sputtering field. It has been found that, unlike the dc case, if the bias is pulsed in this range, the c urrent drawn at the substrate does not saturate, but continues to increase with increasing bias voltage. In addition, this effect becomes more marked as the pulse frequency is increased. For example, under a particular set of operating conditions, a threefold increase in ion current was observed at a bias voltage of -300 V when the bias Was Pulsed at 350 kHz, compared to t he dc case. This phenomenon is believed to be due to the initiation of a se cond discharge at the substrate. Pulsing the substrate bias voltage, theref ore, offers a novel means of controlling the ion current drawn at the subst rate. Clearly, this has significant implications in relation to film growth , sputter cleaning. and substrate preheating processes. Consequently, the v ariation in ion cur-rent with pulse frequency and bias voltage has been stu died for an unbalanced magnetron sputtering system. In addition, substrate heating rates, current-voltage wave forms and plasma characteristics have a lso been investigated. A series of TiO2 and TiN films were then grown under different bias conditions. Analysis of these films showed that the applica tion of pulsed dc power at the substrate can significantly influence film s tructure and properties. In particular, shifts in crystalline structure and texture were observed. (C) 2001 American Vacuum Society.