Formation of carbon nitride films by reactive high-density plasma sputtering with excitation of m=0 mode helicon wave

Abstract

The production of high-density plasmas with excitation of the m=0 mode helicon wave has been studied for the highly reactive sputter synthesis of carbon nitride films in N2 and N2+Ar mixtures in the pressure range of ~0.1 Pa. High-density plasmas of 1012–1013 cm−3 were produced even in pure N2 by using a helical antenna with an azimuthal mode number of m=0. The helicon-wave-excited plasmas have been investigated by wave-magnetic-field measurements and optical emission spectroscopy. The plasma density achieved in 0.26 Pa nitrogen was 4×1012 cm−3 at a radio frequency (RF) power of ∼3 kW and a static magnetic field strength of ∼1000 Gauss. The wave-magnetic-field measurements confirmed excitation of the m=0 mode helicon wave to propagate in the plasmas at the onset of attaining the high-density mode. Significant enhancement of line emissions of atomic nitrogen (N I) and nitrogen ions (N II) was observed in the helicon-wave-excited plasma, whereas the optical emission spectra in the induction mode were dominated by those from the molecular bands of nitrogen. Carbon nitride films have been deposited on a Si(100) substrate by using reactive sputtering of a cylindrical carbon target with the wave-excited high-density plasmas in N2 and N2+Ar mixtures at around 0.1 Pa. Compositional and structural characterization of the CN films was performed by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS), showing that the N/C ratio in the CN films could be controlled up to 1.3. Chemical and structural analysis by XPS has been performed. The XPS analysis showed the existence of peaks indicating a C=C bond and two C=N bonds where nitrogen is bonded to carbon atoms in sp2- and sp3-hybridized states. Nanoindentation measurements showed that hardness values as high as ∼20 GPa were attained at a substrate bias of −200 V.