Abstract: A vapor delivery apparatus for providing a precursor vapor for a vapor deposition process includes a precursor container for holding a liquid or solid precursor. A first temperature control assembly maintains the precursor container at a first temperature to generate a vapor precursor from the liquid or solid precursor. An isolation valve is coupled to the precursor container, and a specific quantity of the vapor precursor is accumulated in an expansion volume. A fill valve, which is coupled to each of the isolation valve and the expansion volume, controls the flow of the vapor precursor from the precursor container into the expansion volume. A second temperature control assembly maintains the isolation valve at a second temperature greater than the first temperature.