Leveraging computational thermodynamics to guide SiC-ZrC chemical vapor deposition process development

Using the CALPHAD approach to understand zirconium carbide deposition, a series of phase equilibria were calculated from a custom thermodynamic database based on a literature source, and the equilibria were used to explore the potential chemical vapor deposition (CVD) processing space in the ZrCl₄-CH₃SiCl₃-CH₄-H₂ system as a function of pressure, temperature, and gas composition. Several gas ratios were considered. At a given ZrCl₄:CH₃SiCl₃ ratio within the range studied, the most important factor was found to be the ratios of CH₄:ZrCl₄, wherein the nature of the composition – carbide vs. silicide – could be controlled. A pure binary composition of ZrC and SiC is expected to form by increasing the initial amount of methane and decreasing the amount of hydrogen from values predicted purely based on thermodynamic equilibrium. Rietveld analysis of the x-ray diffractograms from corresponding experimental depositions confirmed that increasing the CH₄:ZrCl₄ ratio increased the fraction of carbon-containing species (SiC, ZrC) and decreased the fraction of non-carbides (ZrSi, ZrSi₂, etc.), as predicted from the CALPHAD results.