Deposition and characterization of single magnetron deposited Fe:SnOx coatings

Abstract

Coatings deposited by magnetron co-sputtering from a single RF magnetron with a ceramic SnO2 target with iron inset in argon plasma were studied. The mass spectra of the process identified Sn+ and SnO+ species as the dominant species sputtered from the target, but no SnO2+ species were detected. The dominant positive ions in argon plasma are Ar+ species. The only detected negative ions were O−. Sputtered neutral tin related species were not detected. Iron related species were also not detected because their concentration is below the detection limit.The concentration of iron dopant in the tin oxide coatings was controlled by the RF bias applied on the substrate holder while the discharge pressure also has some influence. The iron concentration was in the range from 0.9at.% up to 19at.% increasing with the substrate bias while the sheet resistivity decreases. The stoichiometry ratio of O/(Sn+Fe) in the coatings increased from 1.7 up to 2 in dependence on the substrate bias from floating bias (−5V) up to −120V of RF self-bias, respectively. The tin in the coatings was mainly bonded in Sn4+ state and iron was mainly in Fe2+ state when other tin bonding states were detected only in a small amounts. Iron bonding states in contrary to elemental compositions of the coatings were not influenced by the RF bias applied on the substrate.The coatings showed high transparency in the visible spectral range. However, an increased metallic behavior could be detected by using a higher RF bias for the deposition. The X-ray diffraction patterns and electron microscopy pictures made on the coatings confirmed the presence of an amorphous phase.