Investigation of ion irradiation effects in a-SiXC1-X:H thin films

We present a study of a-SiXC1-X:H films. The films were deposited on Si by an ion beam deposition method using a C6H14 vapour mixture with a hydrogen and silicon source. After deposition the a-SiXC1-X:H layers were irradiated by Ar+ (20-4000eV) beams. Current densities were 0.1-1.5 mA/cm2 and energy densities of the ion beam were 10-400 J/ cm2. The properties of the films were investigated by Raman spectroscopy (RS), ellipsometry, X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), and measurements of electrical resistivity. The RBS showed that a-SiXC1-X:H films have carbon (∼73%), oxygen (∼10%), silicon (∼17%), and less than 0.5% metal contamination. XPS indicated that the oxygen concentration increases in the surface layer after low energy (50-500eV) ion irradiation and the position of the C1s peak shifts to higher energy. This means that the graphite component (peak at 284.3 eV) and C-Si (peak at 283.3eV) decrease and the diamond or C-H (peak at 285.1eV) increases and these changes were bigger at higher ion energy or current density. The optical measurements also showed that ion irradiation improves the diamond-like properties of a-SiXC1-X:H films: the optical band gap increases from 1.53 to 2.27 eV in ellipsometric measurements; the position of the G-band shifts to lower wave number from 1515 to 1505 cm-1; the width (FWHM) of the G-band increases from 153 to 180 cm-1 in Raman spectra. These changes were bigger when the energy density of the ion beam was more than 100J/cm2. RS data suggests that a critical energy density exists (∼100J/cm2) and, after that, the processes were intensified. The electrical measurements confirmed the XPS, RS, and ellipsometry data. We observed an increase in resistivity of a-SiXC1-X:H films, especially, at higher ion energy (3000-4000eV).