Oxidation of Fluorinated Amorphous Carbon (a-CFx) Films

摘要

Amorphous fluorinated carbon (a-CFx) films have a variety of potential technological applications. In most such applications these films are exposed to air and undergo partial surface oxidation. X-ray photoemission spectroscopy has been used to study the oxidation of fresh a-CFx films deposited by magnetron sputtering. The oxygen sticking coefficient measured by exposure to low pressures (<10-3 Torr) of oxygen at room temperature is on the order of S ≈ 10-6, indicating that the surfaces of these films are relatively inert to oxidation when compared with most metals. The X-ray photoemission spectra indicate that the initial stages of oxygen exposure (<107 langmuirs) result in the preferential oxidation of the carbon atoms with zero or one fluorine atom, perhaps because these carbon atoms are more likely to be found in configurations with unsaturated double bonds and radicals than carbon atoms with two or three fluorine atoms. Exposure of the a-CFx film to atmospheric pressures of air (effective exposure of 1012 langmuirs to O2) results in lower levels of oxygen uptake than the low pressure exposures (<107 langmuirs). It is suggested that this is the result of oxidative etching of the most reactive carbon atoms, leaving a relatively inert surface. Finally, low pressure exposures to air result in the adsorption of both nitrogen and oxygen onto the surface. Some of the nitrogen adsorbed on the surface at low pressures is in a reversibly adsorbed state in the sense that subsequent exposure to low pressures ofO2 results in the displacement of nitrogen by oxygen. Similarly, when an a-CFx film oxidized in pureO2 is exposed to low pressures of air, some of the adsorbed oxygen is displaced by nitrogen. It is suggested that these forms of nitrogen and oxygen are bound to free radical sites in the film.