Digital holographic microscopy for the characterization of microelectromechanical systems

Digital holography (DH) in microscopy became an important interferometric tool in optical metrology since when camera sensors reached a higher pixel number with smaller size allowing to acquire more defined images and high-speed computers became able to process such data. Consequently, it was possible the investigation of engineered surfaces on microscale, such as microelectromechanical systems (MEMS) that are microdevices composed by mechanical elements, electronics, sensors and actuators built in a small volume, realized using different material layers superimposed in various process steps, usually starting from a silicon substrate. In DH is necessary to perform the reconstruction of the wave field by means of numerical tools. This entails a computational burden but offers the possibility of retrieving not only the intensity of the acquired wavefield, but also the phase distribution. This work describes the principles of DH and shows some interesting numerical tools suitable to process the holographic images in the field of MEMS. The use of different numerical tools is discussed and illustrated with examples taken from the literature.