MICROSTRUCTURES AND MECHANICAL-PROPERTIES OF AMORPHOUS HYDROGENATED CARBON-NITROGEN FILMS

Amorphous hydrogenated carbon nitrogen (a-C:N:H) films have been deposited on glass, silicon and aluminium substrates by r.f.-plasma-enhanced chemical vapour deposition using C2H2 and N2 gas mixtures in the plasma reactor. An enhanced nitrogen partial pressure leads to a decrease in the hydrogen content and an increase in the nitrogen content of the films as shown by combustion analysis and the IR absorption coefficients for the N-H, C-N and C-H stretching modes. The existence of nitrile groups in a-C:N:H films explains the reduced hardness and stress of the films with increasing nitrogen content. Further, decreases in the optical band gap by 0.5 eV and in the halfwidth of the electron spin resonance line down to 2.5 G are observed, as well as increases in the density of states at the Fermi level by one order of magnitude and in the d.c. conductivity by five orders of magnitude. Temperature-dependent conductivity measurements are consistent with a hopping mechanism around the Fermi level in the temperature range from 170 to 400 K and confirm that the density of states at the Fermi level is the most important parameter for d.c. conductivity. The measurements demonstrate the inefficiency of doping of a-C:H films with nitrogen.