9 March 2013 Fabrication of thin vertical mirrors through plasma etch and KOH:IPA polishing for integration into MEMS electrostatic actuators
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Abstract
We developed a process for the fabrication of thin vertical mirrors as integrated structures of MEMS electrostatic actuators. The mirrors can be implemented as a vertical extension of the actuator sidewall, or can be positioned at any movable part of the actuator. The process involves the fabrication of a mesa structure on the handle layer of a silicon-oninsulator (SOI) wafer through deep reactive ion etching (DRIE). The etch/passivation cycles of the DRIE process were optimized to achieve vertical etch profiles with a depth of up to 200 μm with an aspect ratio of 10:1. The DRIE process introduced typical etch scallops with peak-to-valley and rms roughnesses on the order of 100 nm and 30 nm, respectively. A mask layer was used to pattern a 2.1 μm sacrificial oxide layer for the mesa structure. A second mask layer allowed us to define a large etch cavity for handle layer back-etch. The DRIE etched mesa structure was then etched with diluted potassium hydroxide (KOH) in isopropyl alcohol (IPA). Temperature and etch concentration were optimized for the removal of etch scallops without the formation of ⟨111⟩ etch facets. The etch scallops were almost completely removed and mirror quality surfaces were achieved. The developed mesa structures are suitable for integration into actuators that are patterned in the device layer. A third masking layer, aligned through infrared camera, was used to position the thin vertical mirror at the actuator sidewall. The process provides design flexibility in integrating vertical mirrors of adjustable dimensions to movable elements of MEMS structures.
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M. Q. Huda, T. M. F. Amin, Y. Ning, G. McKinnon, J. Tulip, W. Jäger, "Fabrication of thin vertical mirrors through plasma etch and KOH:IPA polishing for integration into MEMS electrostatic actuators", Proc. SPIE 8612, Micromachining and Microfabrication Process Technology XVIII, 86120D (9 March 2013); doi: 10.1117/12.2005119; https://doi.org/10.1117/12.2005119
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