Magnetron-sputtered Hydrogenated Carbon Nitride: Structural and Optical Properties of As-deposited and Postannealed Films

Amorphous C:H:N thin films were deposited on n-Si and SiO2 substrates at 673 K by RF magnetron sputtering using pure graphite (99.999%) as a target material and mixtures of Ar, N2 and H2 for plasma generation. The dependence of structural and optical properties on nitrogen content was investigated using X-ray photoemission spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) spectroscopy, UV-visible absorption spectroscopy and ellipsometry. Typical stretching modes connected with carbon nitride and diamond-like carbon could be seen in FT-IR spectra. Ellipsometry studies revealed that the optical constants of refractive index (n) and extinction coefficient (k) increased with an increase in nitrogen content. The undesired increase in k value due to increased nitrogen content is attributed to the formation of sp2CN bonds observed by XPS and FT-IR. Optimum conditions for producing transparent films with good values of n and k were determined. The films were subjected to thermal annealing at 873 K and 1073 K in vacuum (≤1 × 10-5 Pa), and postannealing studies were carried out. Annealing caused breakage of undesired sp2CN bonds, which in turn enforced a good effect on the optical property of the films by increasing their optical transmittance.