Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Abstract

Abstract:Tungsten-doped amorphous carbon films with 0-9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the Wrich layer at the surface is carbon free and consists of porous WO 3 . Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.

Erosion of tungsten-doped amorphous carbon films exposed to deuterium plasmas

“…With increasing sputtering time the W 4f 7/2 signal shifts gradually from 31.4 to 32.0 eV corresponding to the tungsten carbide state. This peak position is in good agreement with the binding energy found in as-deposited a-C:W films [24]. Therefore, we assume that at the end of the sputter depth profiling measurements the underlying a-C:W layer has been reached.…”

“…One possible explanation is that the remaining carbon originates from the initial tungsten-carbon chemical bonding in the a-C:W film. Although at low deposition temperature no tungsten carbide crystal is formed in asdeposited a-C:W films, carbide bonds were shown to be the dominant chemical bonding structure of tungsten in a-C:W films [13,[24][25]. It is quite probable that not all carbon in the W-rich layer can be removed by chemical erosion under the conditions of our experiment.…”

Deuterium retention in tungsten-doped amorphous carbon films exposed to deuterium plasma

“…The total remaining film thickness is about 740 nm. From the D depth profile we see that D penetrates this W-rich layer and reaches a depth of 2.5×10 22 atoms/m 2 which corresponds to about 300 nm if the bulk density of amorphous carbon is used [14]. That means that D does not diffuse into the whole remaining a-C:W layer and does not reach the interface to the Si substrate.…”