A high‐flux atomic oxygen source has been developed for the deposition ofinsitusuperconducting highTcfilms under conditions that require low chamber pressures (≤10−4Torr). The source uses a remote microwave plasma to generate the atomic species and is capable of producing an atomic oxygen flux greater than 2×1016cm−2 s−1. The O2dissociation efficiency of the atomic oxygen source is measured to be approximately 25%–30% for an O2flow of 5 sccm. This high efficiency is achieved by the combined effects of a boric acid surface treatment to minimize recombination on the quartz tube and the addition of N2to the oxygen plasma to increase the atomic oxygen yield. We have developed a treatment for the quartz surface that gives reproducible atomic oxygen flux with no degradation of the surface coating with repeated usage.