Characterization of a-C:H:N deposition from CH4/N2 rf plasmas using optical emission spectroscopy

Optical emission spectra (OES) from CH4/N2 rf plasmas, which are used for the deposition of nitrogen-containing hydrogenated amorphous carbon (a-C:H:N) thin films, have been characterized. Previously unidentified spectral lines have been assigned to atomic N. Further identified species include CH, H, H2, N2, N+2, N, and CN. Variations between spectra from the pure CH4 or N2 plasmas and the mixed CH4/N2 plasma are discussed. The enhancement of excited nitrogen species, with the addition CH4, is attributed to Penning ionization. The observed OES variations of the CH4/N2 plasma with power, pressure, and CH4/N2 ratio are explained in terms of possible reaction mechanisms and their activation, and correlated with preliminary film growth characteristics.