Modeling and analysis of nonuniform metal-coating of deeply-etched vertical micromirrors

Abstract

Highly reflective micromirrors have been in high demand in recent decades. This is due to their usage in many systems, such as optical scanners, lab-on-chip spectrometers, and microfabricated structures for gas sensing applications. In these applications, highly reflective micromirrors have been used extensively. Deeply etched vertical micromirrors that have high reflectivity are used in these structures. Upon fabrication using deep-reactive-ion-etching (DRIE) technology, they are coated with metallic layers using the Magnetron Ion Sputtering process. In this article, we investigate the effects of the metallization process of fabricated vertical micromirrors. We derive a model to study the effects of the non-idealities caused by the process, such as the structure's porosity and the metal layer thickness variation, on the reflective performance of the metalized surface. This is investigated using a Gaussian beam sourcewhich is analogous to a single-mode fiber input. The vertical micromirror investigated is composed of a silicon substrate of 1 mm thickness and an aluminum metal layer of thickness that varies from 74 to 82 nm in the vertical direction, which represents a reflection coefficient magnitude that varies from about 89% at minimum metal thickness to about 95% at maximum thickness. The reflected beam is studied in terms of power, skewness and kurtosis.