The polycrystalline. diamond films were deposited on the silicon substrate using a methane/hydrogen gas mixture in a microwave plasma-assisted chemical vapor deposition system. Prior to deposition, the silicon wafers were pretreated by a photoresist in which 0.1 mum powder is suspended. The isolated-diamond film was obtained by etching the backside of silicon wafer with KOH solution. From X-ray photoelectron spectroscopy analysis, the oxygenated phenomenon was detected for the as-deposited diamond film and increased for both surfaces of the isolated-diamond film after the back-etching process. A thick SiC (282.7 eV) and non-diamond components (285 ev) interface layer was found on the bottom surface of the isolated-diamond film. However, it was found that part of the interface layer (SiC and non-diamond components) was removed and the amorphous carbon (285.8 eV) was appeared for the bottom surface of the annealed/isolated-diamond film and the silicon signal was appeared for the top surface of the annealed/isoIated-diamond film. It was also found that the oxygenated phenomenon increased considerably after the 800 degreesC annealing process. However, from the Raman analysis, it was observed that the full width half maximum was changed from 5.0 to 4.6 cm(-1) and from 6.0 to 5.4 cm(-1) for the top and the bottom surfaces of the annealed/isolated-diamond film, respectively. It was concluded that the oxygenated phenomenon increased on both of the top and bottom surface layers of the annealed/isolated-diamond film. However, it was found that the oxygenated phenomenon did not degrade the film quality since the quality of the isolated-diamond film was improved after the high-temperature annealing process.