Optical Profiling Techniques for MEMS Measurement

This chapter reviews the confocal microscopy, a description of the depth-scanning fringe projection system, and an overview about low-coherence interferometric microscopy for the optical profiling of encapsulated Microelectromechanical Systems. The strong depth discrimination of the confocal sensor leads to a good depth resolution. When a depth scan is performed, the peak intensity is measured if the measurement spot falls onto the object surface. The measured confocal intensity signal has to be analyzed relative to a common zero point. The spectrally encoded confocal intensity signal can be used to calculate the topography. The reflected light is focused onto the pinholes of the Nipkow disk, which are also the confocal detection pinholes in this setup. As the microlenses alone cannot do the confocal discrimination, a central pinhole is placed in front of the camera, which can be used for all microlenses in parallel. Confocal microscopes translate the defocus in each position into an intensity signal.