The use of a radio frequency (RF) excited oxygen plasma for cleaning and oxygenation of high Tcsuperconducting films at room temperature is studied by photoemission spectroscopy. Plasma oxidation at ∼10 mT pressure, removes comtaminants like carbon and causes the Ba 5p and 4d and the 0 ls corelevels to shift to lower binding energy. Valence band spectra for an epitaxial Y2Ba4Cu8O15+xfilm on SrTiO3(001) show a Fermi edge and resemble spectra presented by other groups for YBa2Cu3O7single crystals and epitaxial films. These films also show a sharp 0 ls corelevel near 528 eV. Possible reactive ion etching of a degraded YBCO film surface is demonstrated in a series of spectra taken after successive oxygen plasma treatments. A surface contaminated with BaCO3becomes barium deficient after the initial plasma treatment but a second plasma treatment of a substrate biased to −200 V to promote sputtering produces photoemission features typical of an YBa2Cu3O7surface.