OPTICAL-EMISSION SPECTROSCOPY STUDY OF A RADIOFREQUENCY MAGNETRON DISCHARGE USED FOR THE FABRICATION OF X-RAY MULTILAYER MIRROR

We investigated the potential of optical emission spectroscopy (OES) f or accurate control of deposition rate during the deposition of X-ray multilayer mirrors by a radio-frequency magnetron lron sputtrrine tech nique. The behavior of sputtered atom line intensities versus the argo n buffer gas pressure and the r.f. power was investigated and compared to the behavior of the self-bias voltage V-sb, of the sputtered targe t versus discharge parameters. For an usual working pressure p(Ar) = 2 mTorr and tungsten target, the spectral line intensity I, of sputtere d atoms increases with the r.f. power p(r.f.), as I-W alpha P-r.f.(2.2 ) while V-sb alpha P-r.f.(0.6). Deposition rate has been found to incr ease almost quadratically with the power (R-D alpha P-r.f.(2)). I-W wa s found to be relatively insensitive to pressure changes in the 2-10 m TTorr range regardless of the level of the r.f. power used (100-400 W) while V-sb shows a strong pressure dependence. (C) 1998 Elsevier Scie nce S.A.