Ligand Effects in Niobium Precursors for Atomic Layer Deposition of Niobium Oxide Films

We compared two niobium precursors, tert-butylimido tris(dimethylamido)niobium [ t BuN=Nb(NMe 2 ) 3 ] and tert-butylimido tris(ethylmethylamido)niobium [ t BuN=Nb(NEtMe) 3 ], for the atomic layer deposition (ALD) of niobium oxide films. We investigated their volatility, growth behavior, thermal stability, and film properties at temperatures ranging from 150 to 360 °C. Due to its smaller ligands, t BuN=Nb(NMe 2 ) 3 exhibited higher vapor pressures and growth rates than t BuN=Nb(NEtMe) 3 . Pure ALD processes were possible at 170 °C for t BuN=Nb(NMe 2 ) 3 and 200 °C–230 °C for t BuN=Nb(NEtMe) 3 , indicating that t BuN=Nb(NEtMe) 3 has better thermal stability. Density functional theory calculations revealed thermolysis activation energies of 1.68 eV and 1.95 eV for t BuN=Nb(NMe 2 ) 3 and t BuN=Nb(NEtMe) 3 , which correlate with the higher ALD temperature window of t BuN=Nb(NEtMe) 3 . The step coverage, composition, and density of the films were similar for both precursors, with variations depending on the deposition temperature. The films had an [O]/[Nb] ratio of ∼2.5, and the lowest impurity levels were obtained at 230 °C. Film density increased with deposition temperature and saturated at ∼5.1 g cm −3 at 260 °C and above. Both precursors produced high-quality conformal films, but this study reveals an important trade-off: t BuN=Nb(NMe 2 ) 3 offers faster growth, while t BuN=Nb(NEtMe) 3 offers better thermal stability and a wider ALD temperature window.