Effects of coil dc potential on ion energy distribution measured by an energy-resolved mass spectrometer in ionized physical vapor deposition

Abstract

Energy distribution of Ar+ and Ti+ ions and plasma conditions have been investigated for various dc potentials of the rf inductive coil in ionized physical vapor deposition. The sputtering cathode used in the experiment is a conventional magnetron sputtering source with a Ti target (55 mmφ) which is coupled with a rf coil (60 mm φ, made of Cu). The mass spectrometer used to measure ion energy distributions is an energy-resolved type plasma monitor. The coil dc potential is controlled by changing the resistance of the resistor in the termination inductance-capacitance-resistance (LCR) circuit connecting the coil to the ground. By increasing the resistance of the LCR circuit, the peak of the Ar+ energy spectra shifts to a lower energy. In addition, it is found by the probe measurements that the plasma potential decreases with increasing the termination resistance. The changes in the peak energy in the ion energy spectra show a good agreement with the change in the plasma potential; as a result of the change in the plasma potential, the energy distribution of ions accelerated toward the grounded substrate by the sheath shifts to a lower energy in accord with a plasma potential change. In this experiment, plasma potential is strongly affected by the dc self bias of the rf inductive coil induced by a current flow from the ground to the coil through the termination resistance because in the apparatus used the coil was placed inside the chamber.