Atomic layer deposition of crystalline molybdenum oxide thin films and phase control by post-deposition annealing

Molybdenum forms a range of oxides with different stoichiometries and crystal structures, which lead to different properties and performance in diverse applications. Herein, crystalline molybdenum oxide thin films with controlled phase composition are deposited by atomic layer deposition. The MoO2(thd)2 and O3 as precursors enable well-controlled growth of uniform and conformal films at 200–275 °C. The as-deposited films are rough and, in most cases, consist of a mixture of α- and β-MoO3 as well as an unidentified suboxide MoOx (2.75 ≤ x ≤ 2.89) phase. The phase composition can be tuned by changing deposition conditions. The film stoichiometry is close to MoO3 and the films are relatively pure, the main impurity being hydrogen (2–7 at-%), with ≤1 at-% of carbon and nitrogen. Post-deposition annealing is studied in situ by high-temperature X-ray diffraction in air, O2, N2, and forming gas (10% H2/90% N2) atmospheres. Phase-pure films of MoO2 and α-MoO3 are obtained by annealing at 450 °C in forming gas and O2, respectively. The ability to tailor the phase composition of MoOx films deposited by scalable atomic layer deposition method represents an important step towards various applications of molybdenum oxides.