Effect of thermodynamic parameters on properties of silicon-carbon films prepared by radio-frequency plasma-enhanced chemical vapor deposition for anti-reflective and photo-luminescent coatings

Abstract

This work reports an experimental study on the synthesis of hydrogenated amorphous silicon-carbon (a-SiC:H) films with improved antireflective and photo-luminescent characteristics. These films were prepared by plasma-enhanced chemical vapor deposition at a radio frequency of 13.56 MHz, varying the thermodynamic parameters of pressure, gas flows, and temperature. Silane (SiH4), methane (CH4), and hydrogen (H2) were the precursor gases. In a first experiment, composition in gas phase was varied and correlated to the composition in solid phase. Absorption spectra, conductivity, refractive index, optical gap, and photoluminescence (PL) were analyzed. Optical gap and fraction of carbon in gas phase showed a linear dependence with the atomic fraction of carbon in solid phase. Results indicated that the Si0.4C0.6 alloy exhibited a high PL as well as an optimal combination of optical gap and refractive index to be applied as antireflective coating. The subsequent optimization of PL was carried out by a fractional experiment, by varying pressure, H2 flow, and temperature. Results revealed that PL can be improved at high pressure, without H2 flow, and low temperature during glow discharge. Enhancement of PL was correlated to the proper concentration of silicon and carbon in the films, low dark conductivity, negative AM 1.5 conductivity, fluctuating current at low voltage, the increment of Si−H2, C−H2, and C=C bonds, along with vibrational energies in the range of 3190–3585 cm−1.