Single-mask, three-dimensional microfabrication of high-aspect-ratio structures in bulk silicon using reactive ion etching lag and sacrificial oxidation

Abstract

This letter describes a simple method for three-dimensional microfabrication of complex, high-aspect-ratio structures with arbitrary surface height profiles in bulk silicon. The method relies on the exploitation of reactive ion etching lag to simultaneously define all features using a single lithographic masking step. Modulation of the mask pattern openings used to define the features results in etch depth variation across the pattern, which is then translated into surface height variation through removal of the superstructure above the etched floors. Utilization of a nonisotropic superstructure removal method based on sacrificial oxidation enables definition of high-aspect-ratio structures with vertical sidewalls and fine features. The utility of the approach is demonstrated in the fabrication of a sloping electrode structure for application in a hybrid micromirror device.