Plasma diagnostic studies to the carbon nitride film deposition by reactive r.f. magnetron sputtering

Abstract

During r.f. magnetron sputtering of graphite in pure nitrogen the near-substrate plasma has been systematically investigated as to the ionic species and their fluxes on the substrate for various discharge conditions using energy-resolved mass spectrometry in conjunction with probe measurements. These data were related to the chemical composition, bonding structure and internal stress of the deposited carbon nitride films which had been studied by several analytical methods. Besides the process gas ions at which N 2 + and N + are the dominant ones, the r.f. sputter plasma is rich in ionic carbon C i + ( i = 1–5) and ionized groups of C i N j + ( j = 1,2) together bombarding the growing film. The relative net fluxes of these ionic species are strongly dependent on discharge conditions. The total flux was found to be from close to 4 × 10 14 cm −2 s −1 to about 6 × 10 15 cm −2 s −, comparable to the rate of deposited carbon and nitrogen atoms. The mean impact energy of the bombarding ions varies from about 25 eV to 45 eV. The higher values of flux and energy were at high r.f. power and low pressure. The results of the film analyses show that both the power density supplied to the substrate by the ion bombardment and the bombardment energy per condensing atom of carbon and nitrogen are fundamental process parameters of the carbon nitride formation. These parameters were calculated to range from 2 × 10 −3 W cm −2 to about 45 × 10 −3 W cm −2 and from 5 eV to 35 eV, respectively. The overall N/C ratio of the films has a maximum of 0.9 achieved at the lowest power density and runs through a minimum of below 0.4 with increasing power supply to the substrate attributed to desorption of volatile species in this range of power. At increasing ion bombardment energy per deposited carbon and nitrogen atom the bonding structure was found to change from a mixture of graphitic and disordered sp 2-bonded carbon with mainly CN triple bonds to a more disordered phase with predominantly CN double bonds incorporated; this was attended by increasing compressive residual stress within the carbon nitride films. These results may be of importance in finding a way to produce carbon nitride with definite phase by r.f. magnetron sputtering.