Resputtering effects on the stoichiometry of YBa2Cu3Ox thin films

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Abstract
Energetic particle bombardment of the substrate during deposition will under certain process conditions adversely affect the properties of YBa2Cu3Ox thin films. Films were grown by dc magnetron sputtering from stoichiometric compound targets in a planar geometry. An increased oxygen fraction in the sputtering gas entailed a drastic decrease in the film deposition rate. Etching of the substrates was observed in pure oxygen plasmas for pressures below 2 Pa. For the whole range of sputtering gas mixtures, the film composition deteriorated if too low total pressures were used; that is, even if pure argon was used as working gas. Copper deficiency was observed under these conditions and attributed to resputtering of the growing film by energetic particles. This conclusion was supported by the copper deficiency observed in films grown at negative substrate bias, i.e., during ion bombardment from argon plasmas. The origin of various energetic particles during normal sputtering is discussed. We concluded that oxygen neutrals were responsible for the resputtering. At elevated substrate temperatures the film composition was more sensitive to resputtering than at low temperatures. If the energetic oxygen particles were thermalized, stoichiometric films were grown at temperatures up to at least 760 °C.