Composition profiling of graded dielectric function materials by spectroscopic ellipsometry

In this work, the characterization of graded composition layers in transparent materials by spectroscopic ellipsometry (SE) is described. The sensitivity limits were modeled by comparing calculated spectra for samples with and without diffusion profiles at the sample surface for several glass compositions. It was found that for known index profile shapes, the depth sensitivity can be quite high. The sensitivity of the technique increases as the diffusion depth and refractive index contrast increases. The accuracy of the thickness determination depends on the total thickness of the graded layer; for a given system, the accuracy of the composition measurements did not depend on the surface concentration. Leached alkali-aluminosilicate and modified lead silicate glasses were examined by SE to experimentally confirm the modeling predictions on the composition depth profiling. Extremely good correlation between the SE-determined depth profile and SIMS measurements on similar samples was obtained for the case of the modified lead silicate glass. For the aluminosilicate glass, simultaneous roughening of the glass surface during etching makes composition profiling more difficult.