Carbon impurities in oxide thin films: The effect of annealing and laser irradiation

Carbon is a common contaminant in oxide thin film semiconductors that can affect important properties such as the work function, surface chemistry, and electrical conductivity. In this work, carbon impurities in sputtered anatase titania (TiO2) and indium tin oxide (ITO) thin films were investigated using Raman and optical transmission spectroscopy. Annealing in a rough vacuum yielded carbon precipitates, which have characteristic disordered and graphitic carbon Raman signatures. Irradiation by a 532 nm laser in the ambient air was effective in removing the carbon precipitates; in the case of ITO, no trace of carbon could be observed in the Raman spectra following irradiation. The combination of vacuum annealing and laser irradiation could provide a practical means for reducing carbon impurities in thin films.