Journey of a molecule from the solid to the gas phase and vice versa: direct estimation of vapor pressure of alkaline-earth metalorganic precursors for atmospheric pressure vapor phase deposition of fluoride films

Atmospheric pressure (AP) vapor phase processes such as spatial atomic layer deposition (S-ALD) and AP-metalorganic chemical vapor deposition (AP-MOCVD) are becoming increasingly appealing for their use in a variety of academic and industrial applications. Evaluation of precursor vapour pressures is crucial for their application in AP processes and to this aim the Langmuir equation has been applied as a simple and straightforward method for estimating the vapor pressure and vaporization enthalpy of various metalorganic precursors. Using benzoic acid as a calibration reference, the vapour pressure-temperature curves for several alkaline-earth beta-diketonate fluorinated compounds, with molecular formula "M(hfa)(2)center dot L" (with M = Mg, Ca, Sr, Ba; Hhfa = 1,1,1,5,5,5-hexafluoroacetylacetone and L = diglyme, triglyme, and tetraglyme) are derived from their termogravimetric curves. Thus, the enthalpy of vaporization of all complexes has been estimated using the Clausius-Clapeyron equation. As a proof of concept, preliminary results on the use of [Mg(hfa)(2)center dot 2H(2)O]center dot 2diglyme and [Ca(hfa)(2)center dot diglyme center dot H2O] or [Ca(hfa)(2)center dot triglyme] as precursors for AP-MOCVD deposition of MgF2 and CaF2 in the form of thin films are presented. This approach may be used to easily determine vapor pressures of complexes and thus evaluate "a priori" the suitability of a compound as precursor for AP-MOCVD and/or spatial ALD.