Effect of substrate bias on SE, XPS and XAES studies of diamond-like carbon films deposited by saddle field fast atom beam source

Abstract

This paper reports the effect of positive substrate bias ( V s) varying from 0 to 180 V on the spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES) studies of diamond-like carbon (DLC) films deposited using CH 4 gas as a feedstock into a saddle field fast atom beam (FAB) source. The values of optical constants like refractive index ( n) and extinction coefficient ( k) of the deposited DLC films were determined using a two phase model. The values of ‘ n’ were found to fall in the range from 1.505 to 1.720 and ‘ k’ from 0.03 to 0.125 by application of different values of V s. Value of these optical constants were found to decrease with the increase of substrate bias up to 90 V and then increase beyond this value. Position of C 1s peak evaluated from XPS data was found to occur at 286.09±0.18 eV in DLC films deposited by application of different values of V s. Observation of full width at half maximum (FWHM) ( τ) value (1.928 eV at V s=0 V, 2.0 eV at V s=90 V and 1.89 eV at V s=180 V) clearly hinted the existence of a point of inflection in the properties of DLC films deposited using FAB source this way. A parameter ‘ D’ defined as the distance between the maximum of positive going excursion and the minimum of negative going excursion was calculated in the derivative XAES spectra. The values of ‘ D’ evaluated from XAES data for DLC films were found to be 14.8, 14.5 and 15.2 at V s=0, 90 and 180 V, respectively. The sp 2 percentage was calculated for samples deposited this way and was found to be low and lie approximately at 5.6, 2.8, 2.3, 5.7 and 11.5 for different values of V s=0, 50, 90, 150 and 180 V. The sp 3 content percentage and sp 3/sp 2 ratio was found to be 94.4 and 16.7, 97.7 and 42.5 at V s=0 and 90 V, respectively. Beyond V s=90 V these values started decreasing. Mainly, a point of inflection in all the properties of DLC films studied over here at around 90 V of applied substrate bias has been observed, which has been explained on the basis of existing theories in the literature.