Abstract
Interferometry is a powerful and versatile tool for active MEMS characterisation. The high accuracy measurement of deformations and vibrations of MEMS structures is an important application and well described by classical interferometry. Deformation measurements in multi-layered structures requires a more sophisticated approach. All phase changes along the optical path of the object light influence the measurements. Thus the shape and the displacement of obstacles (like glass cover plates) must be included to quantify the measurement results. The paper presents numerical simulations of the light path in an interferometric deformation measurement. A ray tracing program is developed that keeps track of the optical path length and can thus be used to analyse disturbances along the optical path. The simulations show how the deformation of more than one interface influences the phase measurement. The phase errors are quantified and the reliability of the deformation measurements is evaluated. Different interface geometries are examined. The simulations are compared to measurements on a MEMS pressure sensor.