Polymer-like and hard amorphous hydrogenated carbon films prepared in an inductively coupled R.F. glow discharge

Abstract An inductively coupled r.f. discharge was used to prepare amorphous hydrogenated carbon (a-C:H) films in a wide pressure range, at different ion energies, and at different substrate temperatures. Because of the inductive coupling the substrate bias and the r.f. power can be varied independently. The gas pressure ranged from 3 × 10 −2 to 5 × 10 −4 mbar and rather high deposition rates of 30 A s −1 at 8 × 10 −4 mbar have been obtained. Depending on the plasma parameters and the substrate temperature, polymer-like or hard a-C:H films were prepared. Their properties were analysed by IR and visible spectrometry, and measuring the electrical conductivity, the hydrogen content, the Knoop hardness, the adhesion to different substrates, and the internal stress. Strong correlations exist between the optical gap, the relative IR absorption coefficients for the CC vibrational mode, for the integrated CH x ( x = 1,2,3) stretching modes, and the conductivity of the polymer-like films. Measurements of the temperature dependence of the conductivity indicate a superposition of activated conductivity and hopping conductivity at the Fermi level. The hard a-C:H films were prepared with average ion energies between 80 and 330 eV. The films exhibited significant enhancement of the Knoop hardness from 700 kgf mm −2 (7 GPa) to 2000 kgf mm −2 (20 GPa) and density up to 2.0 g cm −3 with increasing ion energy from 80 to 160 eV. A further increase in the ion energy up to about 300 eV does not influence the film properties. Films deposited on silicon wafers had a stress of 1–6 GPa, and the critical load in scratch tests was between 20 and 30 N, being equivalent to an adhesion of about 300 MPa. The influence of the r.f. power (for constant ion energy) on the film properties was also examined.