Thermogravimetric analysis of commercial tungsten molecular precursors for vapor phase deposition processes†

Abstract

Thin films and coatings based on Group 6 metal tungsten (W) have garnered intense interest for applications including catalysis, lubrication, and solar energy. Due to its selectivity and conformality, atomic layer deposition (ALD) has emerged as a key route towards oxides, dichalcogenides, and elemental metal films of W. A key component of the ALD process is the appropriate selection of molecular precursors. Thermogravimetric analysis (TGA) is the primary sorting criterion for precursor suitability and helps delineate probable ALD temperature windows, sublimation/vaporization kinetics, and parameters of decomposition. Currently, a majority of the W materials growth literature is traced to a grouping of commercially available volatile molecular precursors. However, no comprehensive thermochemical analysis exists for all of these precursors, hampering a meaningful direct comparison. Herein, we present an extensive thermogravimetric analysis and direct comparison of commercial volatile W molecular precursors. We report probable ALD temperature windows, enthalpies of sublimation (ΔH_sub), activation energies (E_a), and evaluate thermal stress. Our findings highlight several commercial precursors yet to be reported for ALD growth, but featuring thermochemical properties falling within our suitable observed parametric ranges indicative of potential/viable deposition processes.