Surface characterization and adhesion analysis for polysilicon surface micromachined flaps

Xiaojie Xue; Leslie M. Phinney

doi:10.1117/12.472729

16 January 2003 Surface characterization and adhesion analysis for polysilicon micromachined flaps

Xiaojie Xue, Leslie M. Phinney

Proceedings Volume 4980, Reliability, Testing, and Characterization of MEMS/MOEMS II; (2003) https://doi.org/10.1117/12.472729
Event: Micromachining and Microfabrication, 2003, San Jose, CA, United States

Abstract

Due to the relatively high compliance, large surface-to-volume ratio, and small separation distances, micromachined polycrystalline silicon (polysilicon) structures are susceptible to high adhesion forces including van der Waals, electrostatic, and capillary forces. Since these forces depend on the surface separation distance, it is essential to understand the microtribological properties, especially the surface roughness. In this study, four types of polysilicon microhinged flaps were designed to characterize the surfaces. The flaps enable access to both the top and bottom surfaces of the structural polysilicon layers. Multiple locations are scanned for each surface type using a Digital Instruments 3100 atomic force microscope (AFM). The results indicate that the top surface is much rougher than the bottom surface for structural layers and the roughness is influenced by the adjacent layers. Since the base polysilicon layer (poly0) is six times rougher than a base silicon nitride layer, depositing the MEMS devices on the poly0 layer rather than directly on silicon nitride will reduce adhesion. An adhesion model was used to analyze the effect of roughness parameters on stiction force between structural layers and substrate. Since the tip condition impacts the accuracy of AFM measurement, a wear test of silicon tips was also performed.

Citation Download Citation

Xiaojie Xue and Leslie M. Phinney "Surface characterization and adhesion analysis for polysilicon micromachined flaps", Proc. SPIE 4980, Reliability, Testing, and Characterization of MEMS/MOEMS II, (16 January 2003); https://doi.org/10.1117/12.472729

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