Study of a HPPMS discharge in Ar/O₂ mixture: II. Plasma optical emission and deposited RuO_x film properties

A high power pulsed magnetron sputtering discharge was used in reactive gas conditions for the deposition of conductive ruthenium oxide. In a previous paper (paper I), the physical characterization of the discharge in the case of Ar/O₂ mixtures was studied. This companion paper is devoted to the study of the transition from a metallic working regime to an oxide one. The plasma phase was analyzed with time resolved optical emission spectroscopy. Characteristic Ar I, Ar II and O I emission lines of buffer gas atoms together with Ru I and Ru II ones of sputtered species were followed during the discharge pulse for different pressure values and flow rate composition of Ar/O₂ gas mixture. Conjectures on specific kinetic processes such as Penning ionization and excitation and charge transfer are emphasized in order to interpret the temporal behavior of line emissions. The transition from metallic to oxide regimes, as observed by optical emission, is well correlated with the film stoichiometry and it is rather sharp. This transition was found to be intrinsically free of the hysteresis effect. However, the important modifications of the current and voltage discharge pulses at this transition region makes it difficult to precisely control deposited film stoichiometry.