HYBRID POSTPROCESSING ETCHING FOR CMOS-COMPATIBLE MEMS

A major limitation in the fabrication of microstructures as a postCMOS (complimentary metal oxide semi-conductor) process has been overcome by the development of a hybrid processing technique, which combines bo th an isotropic and anisotropic etch step. Using this hybrid technique , microelectromechanical structures with sizes ranging from 0.05 to si milar to 1 mm in width and up to 6 mm in length were fabricated in CMO S technology, The mechanical robustness of the microstructures determi nes the limit on their dimensions, Examples of an application of this hybrid technique to produce microwave coplanar transmission lines are presented, The performance of the micromachined microwave coplanar wav eguides meets the design specifications of low loss, high phase veloci ty, and 50-Ohm characteristic impedance, Various commonly used etchant s were investigated for topside maskless postmicromachining of [100] s ilicon wafers to obtain the microstructures, The isotropic etchant use d is gas-phase xenon difluoride (XeF2), while the wet anisotropic etch ants are either ethylenediamine-pyrocatechol (EDP) or tetramethylammon ium hydroxide (TMAH), The advantages and disadvantages of these etchan ts with respect to selectivity, reproducibility, handling, and process compatibility are also described.