Harmonic analysis of discharge voltages as a tool to control the RF sputtering deposition process

Masaryk University, Faculty of Science, Department of Physical Electronics, Kotlářská 2, CZ-61137 Brno, Czech Republic, EU

Corresponding author: vasina@physics.muni.cz

Received: 1 October 2008
Accepted: 4 December 2008

Abstract

The reactive magnetron sputtering deposition process controlled by the flow of the reactive gas exhibits processing stability problems. Since the optimal experimental conditions lie very close to the abrupt transition from the metallic to the compound mode, the range at which the films with the right stoichiometry are deposited at high deposition rates is strongly limited and permanent process monitoring is necessary. A sensitive method for the process monitoring is proposed which is based on the measurement of amplitudes of fundamental or higher harmonic frequencies of discharge voltages during the radio-frequency sputtering deposition process. The voltage waveform recorded by the uncompensated probe placed in the vicinity of the plasma contains much higher relative proportion of higher harmonics than the waveform measured on the cathode. Some of the harmonics are extremely sensitive markers of the transition between the two regimes of interest. For example, the amplitude of some harmonics measured by the probe change severalfold by the transition compared to the conventionally used bias on the cathode, which changes typically only by a few percents. The proposed method can even reach the sensitivity of the optical emission spectroscopy mainly for the reactive sputtering of those elements whose sputtering yield does not differ substantially in the metallic and in the compound state.