IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Thursday Sessions
       Session TF-ThP

Paper TF-ThP1
Substrate Response During Dual Bipolar Pulsed Sputtering

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Thin Film Deposition/Carbon-Containing Films Poster Session
Presenter: P.S. Henderson, University of Salford, U.K.
Authors: P.J. Kelly, University of Salford, U.K.
J. O'Brien, University of Salford, U.K.
J.W. Bradley, UMIST, U.K.
P.S. Henderson, University of Salford, U.K.
R. Hall, Advanced Energy Industries UK Ltd.
Correspondent: Click to Email
Dual bipolar pulsed sputtering is a highly successful technique for the deposition of dielectric materials. Operating in the mid-frequency range (20-350kHz), each magnetron acts alternately as an anode and a cathode. With the polarity of each magnetron alternating in this manner, target cleanliness is maintained, anode surfaces are preserved, and long term process stability is achieved. Asymmetric bipolar pulsed DC power supplies are commonly used to drive this process. In such instances, the target voltage during each pulse-off period typically reverses to approximately 10% of the nominal pulse-on voltage, i.e., if the pulse-on voltage is –400V, then the pulse-off voltage will be approximately +40V. However, as pulse frequencies are increased, particularly to in excess of 150kHz, target voltage waveforms increasingly depart from this idealised "square wave" behaviour. Very significant voltage overshoots are observed in each direction during each half of the pulse cycle. In particular, large positive overshoots are observed at the beginning of each pulse-off period. For example, at a pulse frequency of 350kHz, the target voltage can reach a peak value of +500V. Monitoring of the substrate I-V waveforms during operation has revealed that similar transient "spikes" also occur here. As a result, there is a short burst of high energy ions incident at the substrate during each "spikes", and since two targets are in use, these transients occur at twice the pulse frequency. Clearly, such bursts of high energy bombardment could have a significant influence on the growing film. Consequently, an investigation into the complex processes occurring at the substrate during dual bipolar pulsed sputtering has been carried out. A model is proposed to account for the observed phenomena, and the impact on film properties is considered.