STRUCTURAL CHARACTERIZATION OF NIOBIUM FILMS DEPOSITED BY ECR PLASMA ENERGETIC CONDENSATION ON CRYSTALLINE INSULATORS

An energetic condensation thin film coating technique with an electron cyclotron resonance (ECR) induced Niobium (Nb) plasma ion source is used to deposit Nb thin films on crystalline insulating substrates, such as aplane and c-plane sapphire (Al2 O3 ) and on magnesium oxide, MgO (100), (110), and (111). Hetero-epitaxial Nb films were produced by ECR deposition with regulated substrate temperature. The residual resistivity ratio (RRR) of about 1 micron thick films on a-plane (1,1,-2,0) sapphire substrates reach values (350 - 450) comparable to high RRR bulk Nb commonly used for SRF cavities. The epitaxial relationship of Nb/crystalline substrate is found to be strongly influenced by the substrate bias voltage (added to the initial Nb+ kinetic energy, 64 eV), the substrate crystalline orientation, and heating conditions. At low substrate temperature, the Nb films demonstrate crystalline textures, revealed by XRD Pole Figure technique and Electron Backscattering Diffraction (EBSD). Niobium, as most metals, is known to grow with the “Volmer-Weber” growth mode, i.e. island growth. This study shows that the film’s crystal structural character has great impact on its RRR/Tc values.