A Chemical Vapor Deposition Route to Epitaxial Superconducting NbTiN Thin Films

Abstract

The deposition of epitaxial superconducting (Nb,Ti)N thin films is addressed with a new approach, using a chemical vapor deposition technique with in situ production of precursors. Both classic and reactive CVD process are optimized toward (i) the control of crystal structure of the deposited films and (ii) the control of stoichiometry and thus of superconducting properties. Films are chararcterized using thermodynamic, structural, and electrical characterization tools. Precession electron diffraction and electron backscatter diffraction techniques provide the phase and orientation mapping of the films down to the nanometer scale. We demonstrate that the cubic phase (structure with the most prominent superconducting properties) is the thermodynamically stable phase under classic CVD from 800 °C up to 1300 °C. The hexagonal (Nb,Ti)N is formed via a “nitridation like” process under reactive CVD, up to 1200 °C. The composition of the films is controlled by the chemistry of the gas phase, whereas the thicknes...