Diagnostics of direct-current-magnetron discharges by the emission-selected computer-tomography technique

The dc magnetron discharges in Ar are commonly used for thin film deposition. It is essential to investigate the two-dimensional emission profile Φλ(z,r) in order to analyze the geometrical structure of the ring-shaped magnetron discharge. In the present work, an emission-selected computer tomography (ESCT) system was constructed to investigate the three-dimensional structure of the magnetron discharge in Ar. Photons from the discharge are detected by two identical scanning mirror systems, movable both parallel and perpendicular to the electrode, positioned outside the two small orthogonal windows on the chamber. Experiments have been performed in a planar magnetron with an aluminum target having a 100 mm diam and a 20 mm spacing in Ar at a pressure of 0.3 Pa, a current of 40 mA, and a voltage of 290 V. Three lines, Arl(419.8 nm), Arll(434.8 nm), and All(396.2 nm) are selected for the ESCT analysis and discussion of the structure of the discharge. Results from the tomographic imaging showed that the peak in photon production were found at the radius where the magnetic field became parallel to the electrode. The eroded ringlike pattern on the target surface coincided with the radial distribution of photon production in front of the target, and the radial position of the maximum depth of the erosion exactly corresponded to that of the peak emission. The overall features of dc magnetron sputtering were also shown in detail by the present ESCT technology.