Oxygen Effect on the Stability of PECVD Boron-Carbon Films

Abstract
Stability of thin boron-carbon films on silicon substrates was studied. EPMA measurements were used for the film characterization. If the background pressure in the setup was lower than 5x10_-6 Torr the oxygen content in the films did not exceed 3 at.%. The concentration of oxygen in the films increased considerably as a result of bad basic vacuum or insufficient degassing of precursor. While exposed in air for several months the films gradually increased their oxygen content up to 20 at.%. Futher measurements demonstrated no changes in the film composition. The films in which initial oxygen concentration was more than 50 at.% proved to be unstable and tended to disappear at room temperature within a month. Carbon and boron X-ray emission spectra measured by EPMA technique were used to study the chemical bonds in these films. It was shown that the chemical bonds have been formed between boron and oxygen atoms if oxygen concentration exceeded 36 at.%. This phenomenon was not observed for the films with low initial oxygen concentration. The ways of the film evaporation are discussed.