A high-pressure dielectric film curing apparatus, such as a high-pressure batch furnace, is controlled to an elevated cure temperature and super-atmospheric pressure for the duration of the film curing time with the cure pressure achieved at least partially with a vapor of aqueous ammonia in fluid communication with the chamber. The cure temperature may vary, for example between 175° C., and 400° C., or more. The cure pressure may also vary as limited by the saturated water vapor pressure, for example between 100 PSIA and 300 PSIA, or more. The aqueous ammonia may be injected into the chamber or vaporized upstream of the chamber. One or more carrier and/or diluent gas (vapor) may be introduced into the chamber to adjust the partial pressure of ammonia vapor, water vapor, and the diluent.