Atomic Layer Deposition and Superconducting Properties of NbSi Films

Atomic layer deposition was used to synthesize niobium suicide (NbSi) films with a 1:1 stoichiometry, using NbF5 and Si2H6 as precursors. The growth mechanism at 200 degrees C was examined by in-situ quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). This study revealed a self-limiting reaction with a growth rate of 4.5 angstrom/cycle. NbSi was found to grow only on oxide-free films prepared using halogenated precursors. The electronic properties, growth rate, chemical composition, and structure of the films were studied over the deposition temperature range 150-400 degrees C. For all temperatures, the films are found to be stoichiometric NbSi (1:1) with no detectable fluorine impurities, amorphous with a density of 6.65 g/cm(3), and metallic with a resistivity rho = 150 mu Omega.cm at 300 K for films thicker than 35 nm. The growth rate was nearly constant for deposition temperatures between 150 and 275 degrees C but increases above 300 degrees C, suggesting the onset of non-self-limiting growth. The electronic properties of the films were measured down to 1.2 K and revealed a superconducting transition at T-c = 3.1 K. To our knowledge, a superconducting niobium silicide film with a 1:1 stoichiometry has never been grown before by any technique.