Influence of N2/Ar gas mixture ratio and annealing on optical properties of SiCBN thin films prepared by rf sputtering

Optical properties of amorphous thin films of silicon carbon boron nitride (Si–C–B–N) obtained by reactive sputtering has been studied. Compositional variations were obtained by changing the nitrogen and argon gas mixture ratio in the sputtering ambient. The effect of gas ratios and annealing on the optical properties was investigated. It was found that the transmittance of the films increases with nitrogen incorporation. Annealing at higher temperatures leads to considerable increase in transmittance. Optical energy gap (Tauc gap) calculated from absorption data is influenced by annealing temperatures and reactive process gas mixture. Changes in optical properties were correlated to the chemical modifications in the films due to annealing, through X-ray photoelectron spectroscopy. Studies reveal that the carbon and nitrogen concentrations in the films are highly sensitive to temperature. Annealing at higher temperatures leads to broken C–N bonds which results in the loss of C and N in the films. This is believed to be the primary cause for variations in optical properties of the films.