Characterization of membrane curvature in micromachined silicon accelerometers and gyroscopes using optical interferometry

Jeffrey T. Borenstein; Paul Greiff; Jerome B. Sohn; Marc S. Weinberg

doi:10.1117/12.251238

23 September 1996 Characterization of membrane curvature in micromachined silicon accelerometers and gyroscopes using optical interferometry

Jeffrey T. Borenstein, Paul Greiff, Jerome B. Sohn, Marc S. Weinberg

Author Affiliations +

Proceedings Volume 2879, Micromachining and Microfabrication Process Technology II; (1996) https://doi.org/10.1117/12.251238
Event: Micromachining and Microfabrication '96, 1996, Austin, TX, United States

Abstract

Micromachined silicon sensors often exhibit curvature of released membrane structures due to internal stresses, doping gradients, and crystalline defects. This curvature can be a significant source of error in inertial sensors such as accelerometers and gyroscopes. Development of process conditions that reduce curl requires a rapid, accurate method for obtaining high-resolution flatness data over a complex two-dimensional surface. This work reports on the use of a commercially-available, nondestructive optical characterization tool that provides high-resolution profiles of micromachined structures. This interferometry technique is shown to be a significant extension of traditional process development tools, such as scanning electron microscopy (SEM) and test structures. Statistical information on flatness of test structures, accelerometers, and gyroscopes is reported as a function of processing conditions. Unexpected and previously undetected phenomena are revealed by the interferometry measurement. Optimization of the diffusion-annealing cycle provides structures that are flat to within 0.1 micrometers. The flatter parts now being produced have contributed to recent advances in the performance of Draper Laboratory's inertial sensors.

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Jeffrey T. Borenstein, Paul Greiff, Jerome B. Sohn, and Marc S. Weinberg "Characterization of membrane curvature in micromachined silicon accelerometers and gyroscopes using optical interferometry", Proc. SPIE 2879, Micromachining and Microfabrication Process Technology II, (23 September 1996); https://doi.org/10.1117/12.251238

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