Variable angle spectroscopic ellipsometry of fluorocarbon films from hot filament chemical vapor deposition

Hot filament chemical vapor deposition using hexafluoropropylene oxide as t he precursor gas yielded two sets of fluorocarbon films, one with varying O H/COOH content and the other with varying grain aspect ratio, as revealed b y Fourier transform infrared spectroscopy and atomic force microscopy, resp ectively. Variable angle spectroscopic ellipsometry was performed to derive film thickness and film optical constants. A uniaxial Cauchy-Urbach disper sion layer, with separate in-plane and out-of-plane dispersion parameters, was found to realistically describe the films. Derived film thickness agree d well with profilometry measurements. Anisotropy in index of refraction n and extinction coefficient k was on the order of 10(-2) and 10(-5) to 10(-3 ), respectively, The relationship between the complex index of refraction a nd the dielectric function allowed the optical dielectric constant epsilon( 1) to be calculated. The presence of OH did not affect the film optical die lectric consant significantly. Even though OH/COOH groups are considered to contribute adversely by increasing the dielectric constant, their effect m ay have been masked by the dominance of F atoms. The optical dielectric con stant decreased linearly with increasing grain aspect ratio. The presence o f voids was thought to lower the effective index of refraction and optical dielectric constant, and the increase in grain asymmetry created more of th ese voids due to less efficient packing. By assuming a linear contribution from bulk grains and voids to the effective optical dielectric constant, fi lm porosity was derived. A maximum film porosity of 33%, corresponding to a n optical dielectric constant of 1.74, was observed. (C) 2000 American Vacu um Society. [S0734-2101(00)06705-1].