Investigation of niobium nitride and oxy-nitride films grown by MOCVD

Niobium nitride (NbN) and niobium oxy-nitride (NbO_xN_y) thin films were grown by metalorganic chemical vapor deposition (MOCVD) on Si(100) and Si(111) substrates using [Nb(N^tBu)(NMe₂){C(NⁱPr)₂(NMe₂)}₂] [NB; ^tBu = (CH₃)₃C; Me = CH₃; ⁱPr = (CH₃)₂CH] as a simultaneous Nb and N precursor. While NbN films were synthesized under a pure N₂ atmosphere, NbO_xN_y films were synthesized under N₂-O₂ flow (N₂:O₂ = 1-5) in the temperature range 400-600 °C, as well as by NbN deposition followed by ex-situ thermal treatments under flowing O₂ at 400-600 °C. The samples were subjected to a multi-technique characterization in order to elucidate the interplay between their structure, morphology and composition and the adopted processing parameters. Particular attention was devoted to the presence of Nb-N and Nb-O-N phases and their distribution in the films, as well as to surface oxidation phenomena. For the first time, niobium oxy-nitride coatings were obtained by CVD starting from the above precursor compound, with growth rates up to 270 Å/min on Si(111) at 600 °C. The films were characterized by a columnar-like/globular morphology when supported on Si(100)/Si(111) and revealed a higher crystallinity on the latter substrate. Surface and in-depth compositional analyses evidenced a limited carbon contamination and the Co-existence of niobium nitride, NbON and Nb₂O₅. In particular, the presence of the latter in the outermost sample layers was explained by oxidation phenomena occurring upon contact with the outer atmosphere.