A single quality factor for the deposition process of reactively-sputtered thin a-C:H:N films

The carbon bonding modifications, produced by the different deposition conditions in nitrogenated a-C:H films (a-C:H:N) prepared by reactive-sputtering of a graphite target, are investigated by quantitatively analysing the evolution of the D- and G-bands in the Raman spectra. The film C content is evaluated and shown to depend on the many variables involved into the a-C:H:N film growth through a single quality factor, dimensionless combination of the dimensional process-variables. The film structural changes observed are understood in terms of the decreasing sp3:sp2 ratio achieved with the diminishing film C content. The quality factor introduced, able to indicate how the variable-configuration can eventually change without significantly affecting the result in terms of C content and resulting film properties, represents a simple scaling law for the a-C:H:N film deposition, whose validity is preliminarily demonstrated for variations of rf power, total pressure and reactive-gas flow-rate in the ranges from 180 to 300 W, from 20 to 38 mTorr and from 5 to 27 sccm, respectively. A very simple model is therewith proposed accounting for the particular variable combination ultimately effective in determining the final issue of the deposition process. The generality of the proposed method is finally demonstrated.