Thermodynamic Evaluation of ALD Precursors

Studies of the gas phase of organometallic precursors are of interest for several reasons. Firstly, they enable us to assess the thermodynamic properties of the condensed phase (liquid or solid) based on vapor pressure measurements. Secondly, detailed knowledge of the structure and interactions of species in vapors is needed to assess their properties under well-defined conditions, in order to predict and validate their use in deposition reactors. We need to know how they behave at temperature and pressure, and whether there is an entrainment or carrier gas. In particular, studying them in ultra-high vacuum enables us to determine the properties of single molecules or probe elementary reactions, as they are not perturbed by the various factors that often predominate in the condensed phase (e.g. associations due to interactions between molecules or with the solvent, etc.).

This article will present the methods and experimental techniques of thermodynamics dedicated to the gas phase of precursors, and the methods for constructing thermodynamic properties from the structural data of molecules.

The final section will give an overview of how to use thermodynamic data, illustrating the kind of problems it can solve for users of gas-phase atomic layer deposition processes.