Space-resolved velocity and flux distributions of sputtered Ti atoms in a planar circular magnetron discharge

The tuneable diode-laser-induced fluorescence (TD-LIF) technique was used to investigate both velocity and flux distributions of ground-state titanium atoms sputtered from a planar circular magnetron target working at a low pressure (0.4 Pa) and a high pressure (4 Pa). TD-LIF Doppler profiles were measured in front of the racetrack: (i) normal (v(z)) and parallel (v(r)) to the target at several distances (z), and (ii) for different angles (alpha) at 10 mm from the target, addressing the same local volume. The space variation of the velocity and flux distribution functions was deduced with high accuracy from the Doppler shift. Thus it was possible to determine the energetic over thermalized relative atom flux ratio going away from the cathode. The energy distribution function of Ti sputtered atoms in the normal direction is in good agreement with the extended Thompson's formula only for the collisionless sputtering regime, namely in the vicinity of the target and at low gas pressures. Moreover, TD-LIF measurements into the plasma but close to the racetrack centre with different angles of the laser beam show that the angular dependence of the energetic particles is well described by the projection of the normal velocity on each investigated direction. Hence, in this particular plasma region (10 mm in front of the racetrack), the actual angular velocity distribution is mainly governed by the component perpendicular to the target.