Particulates in aluminum sputtering discharges

Plasma-generated particulates are receiving increasing attention as a possible source of device yield reduction in plasma-assisted etching and deposition processes. We have investigated aluminum sputtering in argon discharges between parallel-plate aluminum electrodes under both direct current and radio frequency excitation. Pulsed laser-induced fluorescence experiments indicate that particulates containing aluminum form in these discharges under conditions in which aluminum sputtering takes place. Under sufficiently powerful laser excitation, the laser acts to dissociate the particles, resulting in an enhanced aluminum-atom laser-induced fluorescence signal. Spatial regions of atomic aluminum fluorescence enhancement coincide exactly with nonresonant light scattering profiles from a low-power helium-neon laser. The pulsed laser was observed to locally deplete particulates on a time scale of seconds. Particle profiles appear to evolve in the discharge on a time scale of tens of minutes to hours. The spatial profile of the particles depends in a sensitive manner on the applied voltage, as well as other discharge variables. At a sufficiently negative dc voltage applied to the cathode, particles were observed to be excluded from the interelectrode region.