Cut-and-pasting ligands: The structure/function relationships of a thermally robust Mo(VI) precursor

Abstract

The bis( tert-butylimido)-molybdenum(VI) framework has previously been used for the successful atomic layer deposition (ALD) and chemical vapor deposition of many molybdenum-containing thin films. Here, we have prepared and fully characterized a new thermally robust bis( tert-butylimido)molybdenum(VI) complex, bis( tert-butylimido)-bis( N-2-( tert-butyliminomethyl)pyrrolato)-molybdenum(VI), (tBuN)2Mo(PyrIm)2 (1), that incorporates two N,N’-κ2-monoanionic ligands. The volatility and thermal stability of 1 were measured using thermogravimetric analysis and differential scanning calorimetry, where it was found to achieve a vapor pressure of 1 Torr at 212 °C and had an onset of thermal decomposition at 273 °C. A comparison of its thermal properties with those of the known ALD precursor (tBuN)2Mo(dpamd)2 (dpamd = N,N’-diisopropyl-acetamidinato) showed that 1 had similar volatility but a 78 °C improvement in thermal stability. Preliminary deposition experiments indicated that 1 should be a good ALD precursor; it exhibited self-limiting adsorption and did not decompose on the surface until at least 500 °C, features that will enable its use in the development of new high-temperature ALD processes.

Synthesis, Characterization, and Single-Crystal X-ray Structures of Refractory Metal Compounds as Precursors for the Single-Source Chemical Vapor Deposition of Metal Nitrides

“…Recently we have prepared a series of compounds with the bis­( tert -butylimide)­dichloride­molybdenum­(VI) framework to investigate new vapor-phase precursors. − The thermal properties of these compounds were studied using thermo­gravimetric analysis and differential scanning calorimetry, from which their thermal decomposition pathway was elucidated. , Combined experimental and computational investigations showed that the bis­(imide)­dichloride framework decomposes to first liberate the neutral N , N ′-chelating ligand, followed by γ-hydrogen transfer of the imide ligand, to yield ( t BuNH)­MoNCl 2 and isobutylene, ultimately leading to MoC x N y . Since the imide ligands decompose to afford molybdenum nitride species, we then demonstrated the ss-CVD of high-quality molybdenum nitride films with <2% carbon incorporation .…”

Diverse Post-Metathesis Reactivities of Mixed Amido-Isothiocyanato Molybdenum Complexes

“…Systematic modification of this “parent” species often takes place at amido functions, leading to the recent establishment of new molecular designs for the deposition of pure molybdenum metal films (Figure ). Notably, these new-generation complexes predominantly feature the [Mo­(N t Bu) 2 Cl 2 (L) x ] framework (L = neutral donor, x = 1 or 2), which has been experimentally proven to induce highly desired thermal properties. − However, at the same time, the chlorido (or halido) ligands carry the inherent risk of corrosive byproduct generation, which can be particularly harmful to the metal reactor and the resulting films. Thus, a change to pseudohalides presents a potential solution to bypass this underlying issue, while keeping the molecular scaffold close to well-performed reported systems …”

Put a Ring on It: Improving the Thermal Stability of Molybdenum Imides through Ligand Rigidification

“…We also performed a PES scan of a complex that incorporates an anionic ligand that we previously described, ( t BuN) 2 Mo(PyrIm) 2 (PyrIm = N -2-( tert -butyliminomethyl)-pyrrolato), and showed the same process of rigidification also increases the activation barrier for ligand disociation, and prevents the formation of a κ 1 -intermediate (see SI). This highlights a broader and more applicable application to this process of ligand rigidification because of the number of N,N‘- chelating anionic ligands that are used in vapor deposition precursors; ( t BuN) 2 WCl 2 ·L and ( t BuN)NbCl 3 ·L complexes also followed this trend (see SI).…”

“…The design of new vapor-phase deposition precursors often relies on understanding a compound’s mechanism(s) of thermal decomposition. − These processes must be understood to determine if a compound can produce thin films that contain desirable material properties. Insights into these decomposition pathways can also be used to fine-tune precursors by designing, and incorporating, new ligand scaffolds that block these primary decomposition pathways, or by making them kinetically inaccessible. − This can lead to an overall improvement to the thermal stability of precursors, making them viable at higher temperatures for the deposition of ultrahigh purity thin films.…”