Reactively r.f. magnetron sputtered carbon nitride films

Abstract

Carbon nitride films have been prepared on silicon (100) substrates by reactive r.f. magnetron sputtering of graphite in pure nitrogen to investigate the influence of the ion bombardment on film characteristics. Deposition was carried out at frequencies of 4.00 MHz and 13.56 MHz, respectively, for various discharge conditions in the r.f. power range between 50 W and 1000 W at process gas pressures of 0.3 Pa to 8 Pa and at substrate temperatures up to 500°C. The films were analyzed as to their bonding structure, chemical composition, density and Young's modulus using Fourier transform IR and Raman spectroscopy, electron probe microanalysis and elastic recoil detection analysis. X-ray diffraction and analysis of ultrasonic surface waves. The results indicate that both the energy flux density of the ion bombardment and the bombardment energy per condensing atom of carbon and nitrogen are fundamental internal process parameters for carbon nitride formation. The discharge frequency did not have a remarkable influence on the film features. All CN x films deposited in this way are found to be amorphous. At increasing energy flux density the bonding structure was found to change from a more graphite-like structure with mainly C≡N triple bonds to a more disordered sp 2 bonded carbon phase with predominantly C=N double bonds incorporated. The overall N/C concentration ratio of the films has a maximum of about 1.0 at the lowest energy flux density of the ion bombardment and runs through a minimum of below 0.4 with increasing energy flux density attended by increasing Young's moduli of the carbon nitride films. This is attributed to desorption of volatile species and nitrogen atoms from the surface region of the films. The density of the films increases with the bombardment energy per condensing atom of carbon and nitrogen, but remains below that of graphite.