A design-based approach to planarization in multilayer surface micromachining

This paper describes a design-based planarization strategy that can control topography to within submicron levels. The design concept takes advantage of the inherent conformability of the film deposition processes to achieve planar topography, without the need for an additional planarization step. It is based on a universally regulating line spacing in patterned layers to within a predefined amount, thus allowing subsequent layers to fill in as they grow, conforming to the previous layer. Test structures were fabricated to study the effect of different feature sizes in underlying layers on the topography of subsequent layers. Predictions based on numerical and geometric models for topography generation are compared to fabricated devices. An example of successful application to a micromachined adaptive mirror is presented.