Time-resolved temperature study in a high-power impulse magnetron sputtering discharge

Abstract

The gas heating dynamics is studied in a high-power impulse magnetron sputtering discharge operating in Ar-N2 gas mixtures. The time-resolved rotational temperature analysis based on the spectral transition between the B2Σu+-X2Σg+ energy levels in molecular nitrogen ion (N2+ First Negative Band) is undertaken for this purpose. The rotational temperature in the discharge is found to increase linearly during the plasma pulse being roughly independent on the nitrogen content in the examined range. Such a temperature increase is attributed to the bulk gas heating which is the result of collisions with the sputtered species. Two sputtered materials, Ti and W, are examined during the study. In the case of W sputtering, the gas heating is found to be more pronounced than in the Ti case, which is explained by more efficient energy exchange between the sputtered W atoms and the bulk gas atoms during the plasma on-time. The obtained temperature data are compared to the laser-induced fluorescence study of Ar metastable atoms performed recently in the same discharge in our group. The particularities related to gas thermalization as well as to validity of the utilized approach for characterization of the pulsed sputtering discharges are discussed.