STRUCTURAL MODIFICATIONS IN A-C-H FILMS DOPED AND IMPLANTED WITH NITROGEN

The results of a study on structural modifications resulting from nitrogen incorporation into hard amorphous, hydrogenated carbon (a-C:H) films are presented. Nitrogen-doped films are produced by r.f. glow discharge deposition from CH4-N-2 mixtures onto silicon substrates or by 70 keV nitrogen ion implantation of a-C:H films. The Films were obtained at different N-2, partial pressures (P-N2=0%-50%) and bias voltages (V-b=-200 to -900 V), with a total pressure of P=8 Pa. The ion-implanted films were obtained at fluences of 4-20 x 10(16) N cm(-2). The samples were characterized by nuclear techniques (Rutherford backscattering, elastic recoil detection and nuclear reaction analysis), Raman scattering, Auger electron spectroscopy and the gas effusion method. It has been observed that nitrogen incorporation during deposition does not change the atomic density or hydrogen concentration, although the internal stress is reduced by about 40%. For the implanted samples, a depletion of hydrogen can be determined. The thickness of this depletion layer is of the order of R(p). The internal stress is reduced by a factor of 5 and this is associated with the formation of an interconnected void structure.