Characterization of Structural Stability of Magnetron Sputtered Tungsten-boron Thin Films at Elevated Temperatures

In the divertor of the tokamak type fusion reactors tungsten and tungsten-covered plasma facing materials are currently among the selected materials. However, metallic, high-Z plasma facing materials require plasma mitigation. Recent researches show, that mitigation with boron can be used for optimizing plasma operations, while the interactions between boron containing plasma and tungsten plasma facing materials are less investigated. The formation of mixed layers and their behaviour under plasma operations as well as reactor maintenance procedures needs to be estimated. In order to estimate properties of tungsten-boron mixed layers, such layers can be produced by deposition methods, such as the magnetron sputtering technique and further characterized and analysed. Magnetron sputtered tungsten-boron films were oxidized up to 600 °C. Prior and after thermal treatment infrared spectra and electron microscopy images of the films were registered. For comparison, W films with no addition B of were deposited. Selected parts of the films were etched, to analyse temperature dependent edge effects. Mass changes at ~ 400 – 500 °C can be attributed to the corresponding oxidation processes. The structure analysis and infrared spectrometry show the formation of W-O and W=O bonds. The obtained results will be applied for recommendations for the production of W-B thin films for microelectronic devices.