Dependence of optical properties on composition of silicon carbonitride thin films deposited at low temperature by PECVD

a-SiCN:H thin films were deposited at 150 degrees C by PECVD using silane, methane and ammonia as precursor gases, with a SiH4:H-2 dilution of 1:9. RBS and ERDA were used for determining material composition. The con-centration of silicon, carbon and nitrogen in the deposited films was correlated with the respective precursor gas concentration and the incorporation yield of each atomic species was determined and related to the molecular bond energies of precursor gases. Chemical bonding type and density determined by FTIR were also related to the chemical composition of the films. Optical transmission was measured to estimate the optical gap (E-op) and refractive index (n) in the transparent region. Stoichiometric a-SiN has the lowest n (1.74) and highest E-op (4.12 eV) while a-Si:H presents the highest n (3.37) and lowest E-op (1.85 eV). A trade-off between the E-op and n is presented to show the applicability of this ternary material in optical devices.