The effect of substrate bias in amorphous carbon films prepared by magnetron sputtering and monitored by in-situ spectroscopic ellipsometry

In-situ spectroscopic ellipsometry (SE) was used to study the initial stages of growth and to determine the tetrahedral (sp(3)) C-C bonds, the thickness, and the deposition rate of amorphous carbon (a-C) thin films, deposited by RF magnetron sputtering. The only deposition parameter varied was the bias voltage (V-b) applied onto the substrate from +10 to -140 V. The a-C films were deposited in sequential thin layers and in-situ SE spectra, in the energy region 1.5-5.5 eV, were obtained after the deposition of each layer. The measured SE spectra were analysed by means of the Bruggeman effective medium theory, It was found that V-b is responsible for the development of a-C films of different composition and properties. Differences in deposition rate and sp(3) content were found from the initial stages of growth not only between films deposited with negative and positive V-b, but also between films deposited with (e.g. low, around -5 V and high below -140 V) negative V-b. The latter films developed with V-b between -40 and -80 V were found to be more rich in sp(3) sites than those developed with V-b above -40 or below -80 V. Finally, the deposition rate was found to be almost linear for V-b>0 and power-law-dependent, for V-b<0. (C) 1998 Elsevier Science S.A.