Area selective CVD of metallic films from molybdenum, iron, and ruthenium carbonyl precursors: Use of ammonia to inhibit nucleation on oxide surfaces

The authors demonstrate that the addition of an ammonia coflow during the chemical vapor deposition of MoCxNy, Fe, or Ru thin films at <= 200 degrees C from the metal carbonyl precursors Mo(CO)(6), Fe(CO)(5), or Ru-3(CO)(12) affords area-selective growth: film grows readily on titanium metal or vanadium nitride substrate surfaces, but no nucleation occurs on air-exposed SiO2, TiO2, Al2O3, or MgO within the investigated times of 1-2 h. By contrast, in the absence of ammonia, nucleation and deposition on these oxide surfaces can either be slow or rapid, depending strongly on the oxide surface preparation. NH3 is also the source of N in MoCxNy, which has a resistivity of 200 mu Omega cm and becomes superconducting at a critical temperature of 4K. The authors hypothesize that the passivating effect of NH3 on oxide surfaces involves site blocking to prevent precursor adsorption, or an acid-base interaction to stabilize surface-bound metal subcarbonyl intermediates, or a combination of these mechanisms. A key finding is that surface selective growth is often crucially dependent on the sample history of the substrate, which must be specified in detail if reproducible results are to be obtained. Published by the AVS.