CVD and precursor chemistry of transition metal nitrides

Abstract

Thin films of transition metal nitrides show wide-ranging properties and have various technological uses. The early transition metal nitrides with stoichiometry MNx (M=Ti, Zr, Hf, V, Ta, Cr, Mo and W; 0.50≤x≤1.67) are refractory materials that show metallic conductivity, excellent chemical durability and interesting optical properties. Nitrides of niobium, molybdenum, iron and copper have applications in superconducting photo-detection, catalysis, magnetic recording, and optical storage respectively. Thin films of the transition metal nitrides are commonly prepared by chemical (CVD) or physical vapour deposition (PVD). Although PVD methods have the advantage of tailoring composition with high precision, these materials inherently suffer from epitaxial stresses and strains due to lattice mismatch with the underlying substrate. Films formed by CVD suffer less from such effects as the process relies upon the chemical reaction of precursors. Given the increasing micrometre scale complexity of integrated circuitry topography, the inherent conformality of CVD coatings is sometimes advantageous over existing “line of sight” PVD techniques. As such, there has been a concerted effort to develop CVD techniques and precursors for the low temperature formation of transition metal nitride thin films. This review assesses the various forms of CVD and the precursors employed to deposit transition metal nitride thin films. Where investigated, the precursor chemistry and deposition mechanisms will be presented. When possible, comparisons between precursors and/or CVD method will be made and their effect on the physical/functional properties of the resulting film discussed. This review embodies the versatility of CVD in accommodating a multitude of chemical precursors tailored to the deposition of a wide range of transition metal nitrides.