Measurements of ion energy and flux during ion-assisted deposition of CdTe epilayers by rf magnetron-sputtering

Abstract

Previously we found that the crystallographic structure of CdTe films deposited by means of ion-assisted magnetron rf sputter deposition was very sensitive to the substrate bias voltage and temperature (S. R. Das et al. Can. J. Phys. 65, 864 (1987)). In this work, the ion energy and flux incident on the growing film were determined by means of rf-compensated Langmuir diagnostics. It was found that control of the film phase in the previous work was achieved largely by adjustments of ion energy and substrate temperature; the ion flux changed relatively little. The work is extended to a study of the discharge parameters as a function of rf power, using a CdTe target. The ion and electron densities are found to be sensitive to rf power, whereas the plasma potential Vp and the electron temperature are not. A well-known equation for Vp in terms of the positive excursions of the target voltage gives a poor estimate for Vp because of the voltage drop across the rf impedance of the target disc.