Three-dimensional density profiles of sputtered atoms and ions in a direct current glow discharge: Experimental study and comparison with calculations

Three-dimensional density profiles of the sputtered tantalum atoms and ions have been measured in a direct current glow discharge with flat cathode, by laser induced fluorescence spectroscopy. The primary excitation lines of the tantalum atoms and ions are taken to be the 269.131 nm and the 270.280 nm lines, respectively, whereas the 358.42 nm line and the 304.2 nm line are used as their fluorescence lines, respectively. Moreover, atomic absorption measurements with a hollow cathode lamp were also performed to check the fluorescence results for the atoms. The 271.467 nm line was selected for this purpose. The discharge was studied for a range of voltages, pressures and currents (i.e. 700-1200 V, 0.7-1.6 torr, 1.2-3.9 mA). The atom density profile reaches a maximum at about 3 mm from the cathode, whereas the ion density profile was found to be at its maximum at about 6 mm from the cathode. The experimental data have been compared with results of mathematical simulations for the same geometry; in general, satisfactory agreement is reached. Experimental observations and modeling calculations allow better insight into the complex interactions occurring in a glow discharge. (C) 1997 Elsevier Science B.V.