Preparation and properties of amorphous carbon oxy-nitride films made by the layer-by-layer method

Abstract

Amorphous carbon oxy-nitride films, a-CNxOy, are attractive for obtaining low dielectric constant materials and also for preparing photoconductive materials with a higher optical band gap than amorphous carbon nitride films, a-CNx. We found that oxygen plasma processes on a-CNx have two effects: etching and oxidation in the preparing process of amorphous carbon oxy-nitride films a-CNxOy. Because it was not possible to make films by mixing a small amount of oxygen to nitrogen as a reacting sputter gas, we have prepared LLa-CNxOy in a layer-by-layer process, which consists of a cyclic process of deposition of a thin amorphous layer a-CNx by nitrogen-radical sputtering of a carbon target and of an oxygen plasma treatment on a-CNx. By a layer-by-layer process of 60–120 cycles, we have tried to homogenize the distribution of oxygen atoms in LLa-CNxOy. Defect densities, infrared absorption spectra and UV-Vis absorption spectra to obtain the optical energy gap Eo were used to characterize LLa-CNxOy films. From infrared spectra, the peaks related to carbon and oxygen were confirmed to increase in LLa-CNxOy films. LLa-CNxOy with Tauc optical energy gaps up to 2.67 eV were prepared, whose value was larger than the 1.5–2-eV value of a-CNx.