Electronically probed measurements of MEMS geometries

Measurement of microelectromechanical systems (MEMS) geometry is critical for device design and simulation, material property extraction, and post-fabrication trimming. In this paper electrostatically driven laterally resonant comb-drive test structures with prescribed changes in spring width are used to ascertain systematic variations in process offsets (edge biases) and sidewall angles. The technique is both in situ and nondestructive. An analytical model for the resonant frequency, tuned with three-dimensional (3-D) simulations using MEMCAD, includes effects of a distributed mass, residual stress, and compliant supports. The model is corroborated by 3-D numerical simulations to validate the extraction approach. Fits of this model to experimental data determine the offset and sidewall angle of polysilicon devices fabricated by the Multi-User MEMS Processes of the Microelectronics Center of North Carolina, Research Triangle Park, NC.