Evolution of line-edge roughness during fabrication of high-index-contrast microphotonic devices

Abstract

We have investigated the evolution of line-edge roughness during fabrication of high-refractive-index-contrast microphotonic devices. First, we present a method for estimating the spectral density of line-edge roughness. Then, the effect of common fabrication steps on line-edge roughness is reported. Spectral-density estimates are obtained from high-resolution micrographs acquired with a scanning electron microscope. Line edges are detected in the micrographs and then analyzed using various statistical methods. The impacts on roughness of liftoff, reactive-ion etching, and two non chemically-amplified electron-beam resists are quantitatively evaluated. We found that smooth sidewalls require adequate coverage of sidewalls via polymerization during reactive-ion etching, and a sharp resist profile when liftoff is used. In general, roughness can be greatly reduced by adjusting fabrication parameters. The method described in this article can be used as an efficient process optimization tool for fabrication of high-refractive-index-contrast microphotonic devices.