Analysis of dielectric constants to determine sp(3)/sp(2) ratio and effect of substrate bias on spectroscopic ellipsometric studies of tetrahedral amorphous carbon films grown using an S bend filtered cathodic vacuum arc process

摘要

The carbon bonding ratio and optical properties have been studied by spectroscopic ellipsometry of as grown tetrahedral amorphous carbon (ta-C) films, deposited using in S bend filtered cathodic vacuum arc (FCVA) process. First, the carbon bonding ratio in ta-C films has been estimated from imaginary part of dielectric constant (epsilon(2)) spectra obtained by spectroscopy ellipsometry. A method has been developed to find out the fractions of sp(3) and sp(2) bonded carbon atoms from the Wemple-Didomenico plot. Second, the effect of varying negative substrate bias on the optical properties and sp(3)/sp(2) ratio of as-grown ta-C films has been made. The values of the optical constants evaluated are found to increase with the increase or the negative substrate bias in the as-grown ta-C films but the values of sp(3)/sp(2) ratio and the optical band gap (E-g) evaluated increase up to -200 V substrate bias and beyond -200 V substrate bias the values of sp(3)/sp(2) ratio and E-g decrease. Application of substrate bias is, thus, found to increase the sp(3) bonding and E-g up to -200V substrate bias and beyond -200V substrate bias there is reversal of the trend.