Comparison of direct current and radio frequency argon magnetron discharges by optical emission and absorption spectroscopy

Abstract

A magnetron sputtering discharge is studied by optical emission and absorption spectroscopy, following an experimental design procedure. The 33-mm-diam target is made in an aluminium base alloy. The radiation is focused on an optical fiber and is spectrally analyzed in a Jobin–Yvon computer-controlled 1.0 m Czerny–Turner scanning monochromator. The spatial resolution is 2 mm. Emission line intensities from the Ar sputtering gas and the sputtered species are studied as a function of geometrical and physical discharge parameters: excitation mode (rf or dc), target thickness, gas discharge pressure, electric power (rf) or current (dc), and the distance from the target. In emission spectroscopy, two Ar I lines are studied: Ar I 425.9 nm 3p55p(3p1)−3p54s(1s2) and Ar I 451.1 nm 3p55p(3p5)−3p54s(1s2) and also an Ar II line 442.6 nm 3p44p(4D0)−3p44s(4P). The first excited level configuration of Ar (3p54s) contains two metastable (1s5,1s3) and two resonant (1s4,1s2) levels. The Al excited and ground states have also been analyzed: the Al I 3p2P0−4s2S and Al I 3p2P0−4s2S. By use of hollow-cathode lamps, absorption due to aluminum atoms and argon metastable and resonant atom states densities are evaluated, as a function of the same parameters as in emission. The experimental responses (emission and absorption intensities) are fitted by a quadratic equation in which interactions between factors are included. The influences of the main factors are deduced and discussed.