Structural and optical investigation of plasma deposited silicon carbon alloys: Insights on Si-C bond configuration using spectroscopic ellipsometry

Abstract

Amorphous (a–Si1−xCx:H) and microcrystalline (μc–Si1−xCx:H) thin films have been deposited by plasma-enhanced chemical-vapor deposition using SiF4–CH4−H2 rf plasmas. Gas flow rates have been varied to deposit films with different carbon content and microstructure. The microstructure and optical properties have been investigated by IR/Raman spectroscopy and by spectroscopic ellipsometry in the energy range of 1.5–5.0 eV. Ellipsometric spectra have been analyzed in terms of the tetrahedron model combined with the Bruggeman effective-medium approximation to determine the film microstructure and silicon–carbon-bond configurations. Correlation between Si–C bond configurations and optical properties of films has been studied as a function of carbon content and microstructure. It is found that the optical properties and the band gap value depend not only on the carbon content, but also on the Si–C bond configuration and microcrystallinity. The films consist of Si-centered Si–Si4−vCv(v=0–3) Si-centered tetrahedra with segregation of μc–Si. The amorphous matrix changes from Si–Si3C to Si–SiC3 with the increase of the μc–Si phase. The optical gap is found to increase with both carbon content and microcrystallinity.