ABSTRACT
In this chapter, we demonstrate a low-cost and multifunctional interferometric platform based on a Twyman–Green interferometer (TGI) for testing microelectromechanical systems/microoptoelectromechanical systems (MEMS/MOEMS). This technique may be used for relatively smooth surfaces to measure the three-dimensional map of out-of-plane displacements. It provides both micromechanical and material properties of buckled membranes, quasistatic actuator behavior, and vibrational analysis of microdevices. In Section 12.3, specific metrology procedures have been demonstrated to determine the residual stress of silicon membranes prestressed by silicon oxinitride (SiOxNy) grown by plasma-enhanced chemical vapor deposition (PECVD). Because the material properties of SiOxNy films depend strongly on details of the PECVD process, the relationship between the micromechanical properties, physicochemical characteristics, and, finally, the optical properties of SiOxNy thin films are established carefully. In Section 12.4, the polysilicon scratch drive actuator (SDA) is used as an example structure for demonstrating the applications of interferometry for the determination of actuator performance. A better understanding of the driving and stiction mechanisms is given precisely by the length of such contact interactions that could lead to the optimization of SDA design. Interferometric technique measures complete deflection curves of the electrostatically actuated SDA plate. The experimental results obtained by this technique are compared with numerical data calculated by FEM. When operating under a stroboscopic regime, the same interferometer allows the full-motion measurement of moving microstructures, demonstrated in the case of the response of a piezoelectric actuator and electrostatically driven torsional mirror. The concept of new generation of industrial test equipment for microproduction is introduced in Section 12.6. It is based on a parallel inspection approach. An array of microinterferometers integrated on a probing wafer is adapted to the MOEMS wafer under test and provides 25 measurements within one measurement cycle.
