Monitoring Removal of W Layer from Ag Substrate Using Balmer-α Emission of Backscattered Hydrogen Atoms in Low Density Gas Discharge
S. Ertmer, O. Marchuk, S. Dickheuer, S. Heuer, P.H. Mertens, M. Rasinski, B. Göths, S. Brezinsek, A. Houben, Ch. Linsmeier, A. Kreter
Forschungszentrum Jülich GmbH - Institut für Energie- und Klimaforschung-Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
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The Doppler-Shifted Reflectance Measurements diagnostic is applied for in-situ measurements of a total spectral reflectance of the sample during the transition phase induced by physical sputtering of a layer of tungsten (W) from an silver (Ag) substrate. The sputtering of a 4 mm layer of W is monitored at the Balmer-α line λ0=656 nm with a temporal resolution of 60 s corresponding to a thickness of ~λ0/100 in the absence of other light sources. The sample was exposed to a mixed argon (Ar) and hydrogen (H) gas discharge in the linear plasma device PSI-2, where the Ar+ ions, accelerated by the applied negative potential of -180 V, were intrinsically used for sputtering of the deposited film. The sputtered W or Ag were also monitored by optical emission spectroscopy. It is shown that in low density gas discharges the Doppler-Shifted Reflectance Measurements diagnostic is, in providing the value of reflectance, extremely sensitive to the transition phase between W and Ag - as compared to resorting to the W-I and Ag-I emission lines intensities. It could thus be directly applied to cleaning plasma discharges with the presence of Ar and H or deuterium (D) ions.

topics: Balmer lines, sputtering, emission spectroscopy, thin films, line shape