Thermodynamic analysis of liquid source chemical vapor deposition process for the preparation of a Ba-Sr-Ti oxide film

The equilibrium concentrations of the chemical species in a Ba-Sr-Ti-C-H-O system, corresponding to a liquid source chemical vapor deposition (LSCVD) process used in the preparation of barium strontium titanium oxide (BST) films, were determined by thermodynamic calculations. Ba(dipivaloylmethanato)(2), Sr(dipivaloylmethanato)(2), and Ti(tetra-isopropoxide) were assumed as the metal sources, and tetrahydrofuran (THF) and O-2 as the solvent and oxidant, respectively. An increase in the amounts of THF, a major source of graphite production, significantly increases the equilibrium concentrations of metal oxides and carbonates in the system. On the other hand, an increase in the O-2 content decreases the graphite content and increases the amount of carbonates. Based on these results, the conditions for an LSCVD process that produces minimum amounts of carbon impurities in a BST film were identified as a function of the process temperature and the O-2/THF ratio. The results of the equilibrium calculations are in reasonable agreement with experimental data, which indicates that the results can be used as a basis for identifying LSCVD conditions needed to prepare BST films with defined compositions.