A Microelectronics-Compatible Process for Surface Micromachining of MEMS and MOEMS

Many fabrication steps for micro electromechanical and micro optoelectromechanical systems (MEMS and MOEMS) are carried out on specialized or highly customized tools that are not part of a standard microelectronics process flow. This paper presents a surface micromachining process for electrostatically-actuated MEMS devices using standard microelectronics tools, materials, and process conditions. The result should facilitate MEMS development in university laboratories with a microelectronics focus, and encourage the transfer of MEMS production to aging or underutilized industrial facilities. Aluminum structures, with silicon dioxide or silicon nitride dielectric layers, are built upon a silicon or glass wafer substrate. Shipley SC1827 photoresist provides a 2.7 μm thick sacrificial layer. The release etch is the critical fabrication step. This must be a dry process to avoid stiction, should be isotropic to minimize the etch time, and should be capable of large undercut distances to minimize the need for etch holes. Finally, the etch must be sufficiently selective to allow for the necessary release etch time without significantly impacting non-sacrificial structures. An O₂/CHF₃ plasma etch has been developed to meet these requirements. Using this process we have designed, fabricated and tested structures with moveable mirrors suspended over multiple drive and sense electrodes.