Plasma erosion of a magnesium radio-frequency cathode measured by laser-induced fluorescence

Various diagnostic methods are compared with respect to their abilities in determining the controlled electrode erosion in a radio-frequency (rf) plas ma source. The source is cylindrical in shape with a center rf cathode made of magnesium. Due to the unequal electrode area ratio of 1:8 a high self-b ias voltage develops. Sputtering from the cathode was studied by means of o ptical emission spectroscopy, laser-induced fluorescence (LIF), quadrupole mass spectrometry, and deposition experiments. Dependencies of the plasma p arameters were measured. The magnesium density decreased exponentially with distance from the target but could be traced down to very low levels aroun d 10(5) cm(-3) in the downstream region by the extremely sensitive LIF meth od. Laser excitation from the electronic ground state as well as fluorescen ce detection were performed on the strong 3p P-1(1)0 <-- 3s S-1(0) resonanc e line at 285.2 nm. For absolute calibration Rayleigh scattering from cold nitrogen gas was utilized. Sensitivity issues and detection limits are disc ussed. (C) 2000 American Vacuum Society. [S0734-2101(00)01103-9].