Application of Optical Emission Spectroscopy for Predicting the Composition of Films in Reactive Magnetron Sputtering of Ti–Al Composite Targets

Abstract—

The processes of reactive magnetron sputtering of Ti–Al composite targets with varying Al/Ti ratios were studied. Dependences of deposition rate, discharge voltage, elemental composition, and intensity of reference plasma emission lines were determined as functions of the oxygen concentration in the Ar–O₂ gas mixture. It was demonstrated that, in reactive sputtering of Ti–Al composite targets, the discharge voltage is determined by the effective ion–electron emission coefficient (IEEC), which depends on the area occupied by the metals on the target, their oxidation states, and the IEEC of the metals and their oxides. The deposition rate of Ti_xAl_{1 – x}O_y films both in the metallic and transitional sputtering modes increases proportionally to the fraction of Al in the target, and the relative concentration of the metals in the deposited films depends on the oxygen concentration in the Ar–O₂ gas mixture and is determined by the reactivity of the constituent materials in the target. By optical emission spectroscopy (OES), it was shown that the ratio of the atomic concentrations of Al and Ti in the deposited Ti_xAl_{1 – x}O_y films uniquely depends on the ratio of the intensities of the aluminum emission line (AlI) and the titanium emission line (TiI) in the plasma. This allows using OES for predicting the metal contents in the films in reactive magnetron sputtering of Ti–Al targets.