Mixed amido/imido/guanidinato complexes of niobium: potential precursors for MOCVD of niobium nitride thin films

Abstract

Novel mixed amido/imido/guanidinato complexes of niobium are reported. The complexes were synthesized by insertion of two equivalents of di-isopropylcarbodiimide (i-Pr-cdi) or bis-cyclohexylcarbodiimide (Cy-cdi) respectively, into the niobium-amido bonds of [Nb(NR(2))(3)(N-t-Bu)] (, R = Me; , R = Et) starting out from [NbCl(3)(N-t-Bu)(py)(2)] and the respective LiNR(2) reagent (py = pyridine). Four representative examples of these mixed ligand amido/imido/guanidinato compounds were synthesized and were characterized by (1)H-NMR, (13)C-NMR, (15)N-NMR, CHN-analysis, mass spectrometry and infra-red spectroscopy. The molecular structures of [Nb(NR(2)){eta(2)-(i-Pr-N)(2)C(NR(2))}(2)(N-t-Bu)] (, R = Me; , R = Et) in the solid state were determined by single-crystal X-ray diffraction studies and are discussed together with the molecular structure of the starting compound [Nb(NMe(2))(3)(N-t-Bu)] (). The thermal properties of the new compounds depend on the substitution at the guanidinato ligand. Complexes of i-Pr-cdi are significantly more volatile than complexes of Cy-cdi as revealed by thermogravimetric analysis. Preliminary experiments using as a single-molecule source for metal-organic chemical vapour deposition (MOCVD) in the absence of ammonia indicate the formation of the stoichiometric, and surprisingly carbon-free, cubic niobium nitride phase.

Deposition of Niobium Nitride Thin Films from Tert‐Butylamido‐Tris‐(Diethylamido)‐Niobium by a Modified Industrial MOCVD Reactor

“…This value is in good agreement with the lowest reported amounts of carbon inside a niobium nitride thin film deposited by MOCVD. [14,17] …”

“…Otherwise, it is well known that niobium nitride films with very low carbon content can be deposited by MOCVD using all-nitrogen coordinated niobium complexes in the absence of ammonia or hydrazine (see introduction). [17] Anyway, the chemical form of incorporated carbon impurities was never investigated in detail. In the present case, the assignment of the low BE signal at 282.8 eV to NbC species was further corroborated by the deconvolution of the Nb 3d photopeak, that was performed by means of three different spin-orbit doublets.…”

“…The presence of ammonia is necessary to minimize carbon incorporation. [14,17] Following our preliminary work, [27] the present paper aims at providing a deeper insight into the system microstructure, composition, morphology, and electrical properties. In particular, the deposited films revealed specific resistivities as low as 500-600 mV cm and a work function of 4.72 eV.…”

“…[17] Metallic, golden-colored films containing the pure d-NbN phase were deposited at substrate temperatures ranging from 400 to 600 8C, under nitrogen atmospheres. Carbon levels were lower than 3 at.-%, but high oxygen amounts (up to 15 at.-%) were present in the films.…”

MOCVD of Niobium Nitrides and Oxy-Nitrides using an All-Nitrogen-Coordinated Precursor: Thin-film Deposition and Mechanistic Study

“…In this context, niobium nitride is a promising material to serve as a diffusion-barrier against copper migration (1)(2)(3). A related material to -NbN is cubic -TaN, which has been proven to fulfill most of the required features for diffusion-barriers (4)(5)(6).…”