Negative ion density measurements in reactive magnetron sputtering

Abstract

A combination of laser photo-detachment and conventional Langmuir probing has been used to obtain the bulk negative ion density in both a DC and radio frequency (RF) sputter magnetron. The argon and oxygen discharges were operated at low powers and over a range of pressures. The photo-detachment signal is expected to reach a limiting value; however, the signal continues to increase with laser energy density and this can be attributed to a laser ablation effect. In the RF magnetron the electron temperature [Te) in oxygen decreased with increasing pressure, whereas the electron density (Ne) increased from 0.53 to 8.6 × 1014 m-3. At around 12 mTorr, a sudden increase in Ne by 3.7 is accompanied by a small drop in Te. The negative ion density (N-) also increases with pressure reaching a maximum of 1.7 times; 1014mr-3 between 5 and 10 mTorr. Under similar conditions, the DC magnetron negative ion fraction (N-/Ne) is estimated to be ∼0.01, being significantly lower than in the RF magnetron where N-/Ne≈1. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.