Comparative study of various release methods for polysilicon surface micromachining

This paper presents an objective comparison of various release techniques for polysilicon surface micromachining using identical test structures made by MCNC Multi-User MEMS Processes (MUMPs). Test structures of varying width and length were prepared using five different releasing procedures - evaporation drying with deionized water and methanol as final rinsing liquids, sublimation drying using p-dichlorobenzene and t-butyl alcohol, and CO2 supercritical drying. Both sublimation drying methods as well as supercritical drying rendered good results with 2 mu m thick, 2 mu m gap polysilicon cantilevers up to 700 mu m in length. In addition, the systematic test in this study reveals, for the first time, that the maximum beam length obtainable increases as the beam width increases for the case of sublimation, opposite to the well known case of evaporation drying. In the course, we also introduce a new setup that considerably improves the way sublimation is used for releasing.