J. Vac. Sci. Technol., A, 16(2), 624-627 (1998).
Hayden, D. B., Juliano, D. R., Green, K. M., Ruzic, D. N., Weiss, C. A., Ashtiani, K. A., Licata, T. J.
A rotating magnet dc planar magnetron with a 33-cm diameter aluminum target is coupled with a secondary plasma source to ionize the sputtered metal neutral flux to control the angular distribution of the flux arriving at the surface of the substrate. For this purpose, a radio-frequency (rf) plasma is created between the sputtering target and substrate by a three-turn coil located in the vacuum chamber. The rf plasma increases the electron temperature and density, which results in significant ionization of the neutral metal flux from the sputtering target. By applying a small negative bias to the substrate, metal ions are drawn to the substrate at normal incidence. A gridded energy analyzer and a quartz crystal microbalance (QCM) were used to determine the ion and neutral deposition rates. From this, the ionization fraction of the flux incident onto the QCM is determined.