Postanalyses of an optical multilayer interference filter using numerical reverse synthesis and Rutherford backscattering spectrometry

Abstract

Post nondestructive analyses of an all-dielectric multilayer Fabry-Perot interference filter developed through a reactive electron beam deposition process have been carried out through numerical reverse engineering of transmission spectra, Rutherford backscattering spectroscopy and quartz crystal monitoring data to derive multilayer geometry, deposited layer thicknesses, densities, refractive indices, compositions, and stoichiometry. These techniques are collectively used to fulfill the missing links with complementary and some supplementary information to inverse synthesize the multilayer geometry. During this investigation it is distinctly understood that the factors associated with real-time deposition have significantly influenced the microscopic parameters, namely, the densities and refractive indices of TiO2 and SiO2 layers. This in turn influenced the layers' geometric (physical) thicknesses during automated quarter-wave optical layer monitoring and consequently affected the experimental spectral characteristics. The role of oxygen has been observed to be significant in controlling the mass densities of these refractory oxide layers. It is further noticed that the layer density values have been significantly perturbed whether the associated TiO2 or SiO2 oxide dielectric films are substoichiometric (oxygen-deficient), stoichiometric, or superstoichiometric (oxygen-enriched).