Energy resolved angular distribution of argon ions at the substrate plane of a radio frequency plasma reactor

Abstract

The energy resolved angular distributions of argon ions of a 13.56 MHz rf discharge bombarding the powered electrode in a parallel plate reactor are investigated. Argon ions from the plasma are sampled through a small orifice in the powered cathode and are analyzed using a quadrupole mass spectrometer equipped with an energy filter. The angular resolution of the instrument is slightly better than 1°. The process pressure ranges from 5 to 50 mTorr and the rf power is varied to yield dc bias potentials between −100 and −450 V. The measured energy distributions of argon ions extend from 0 eV up to a maximal energy corresponding to the dc bias potential and exhibit significant structures which are explained by the effect of collisions in the sheath combined with rf modulations of the sheath potential. The principle structures in the ion energy distributions are nearly independent from the angle of ion trajectories with respect to the electrode normal. The energy resolved ion angular distributions are investigated in the range between ±3° and show structures which may be resulting from charge exchange collisions and elastic scattering of ions in the sheath. Angular distributions centered around the surface normal are found with angular widths between 1° and 2°. Furthermore, extrema at angles between 1° and 2° are detected for distinct energies and plasma parameters.