Optical Properties of Nitrogen-Rich Carbon Films Deposited by dc Magnetron Sputtering

M. Friedrich, D.R.T. Zahn
Technische Universität Chemnitz, Institut für Physik
Halbleiterphysik
D-09107 Chemnitz
Germany

Th. Welzel, H. Kupfer
Technische Universität Chemnitz, Institut für Physik
Technische Physik / Physik fester Körper
D-09107 Chemnitz
Germany

R. Rochotzki
Technische Universität Chemnitz, Institut für Physik
Gasentladungs- und Ionenphysik
D-09107 Chemnitz
Germany

Nitrogen-rich carbon films were grown by dc magnetron sputtering from a graphite target in various nitrogen/argon gas mixtures using two different substrate temperatures. Infrared spectroscopical investigations were carried out in order to determine differences in the film composition and structure caused by the variation of the deposition conditions. The spectra are interpreted in terms of two bands which are typicall found in the Raman spectra of CN_x. While the band at 1280 1/cm only slightly inreases in absorption intensity with increasing nitrogen incorporation the band at 1520 1/cm becomes much more pronounced. Both bands shift to higher wavenumbers with increasing nitrogen content. Additionally, the films show a decrease in the absorption above 2500 1/cm. The existence of different functional groups absorbing at 2130 1/cm can be suppressed by substrate heating up to 400 °C during preparation, CN groups absorbing at above 2200 1/cm, however, remain in the samples. In order to support the IR results additional ellipsometric measurements, investigation of film density and stoichiometry were performed. Heating the substrates during deposition leads to a reduced nitrogen incorporation.