Investigation into the mechanism of ductility of thin amorphous Ta2O5 films

Thin films (300-800 A) of tantalum metal were successfully sputter deposited on uniformly deformable fluoropolymer and polyimide substrates in stress free form. The crystal structure of the deposited Ta films depends mainly on the sputtering parameters. These films were later anodized into amorphous Ta2O5 which is a non-porous (barrier-type) oxide with excellent corrosion resistant properties. Ta2O5 films were also obtained by direct electron beam evaporation (EBE) of Ta2O5 on different metallic and polymeric substrates, XPS and AES studies were carried out on Ta, anodic and EBE Ta2O5 films to determine the chemical composition and oxidation states of elements. Thin Ta and Ta2O5 films on fluoropolymer substrates contained fluorine as an impurity while similar films on polyimide contained no fluorine and, in general, fewer impurities. EBE Ta2O5 films gave a stoichiometric O/Ta ratio all through the film thickness while the presence of suboxides and adsorbed OH group in anodic films was suggested by XPS and confirmed by FTIR absorption characteristics. Both thin Ta film and the corresponding anodic oxides, when deformed at room temperature to 10% strain, exhibied the ductile behavior of metals where slip bands were observed in the electron microscope. On the other hand, EBE Ta2O5 films failed in a brittle manner when deformed beyond 1% tensile strain at room temperature