Miniaturized Diffraction Based Interferometric Distance Measurement Sensor
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In this thesis, new metrology hardware is designed, fabricated, and tested to provide improvements over current MEMS metrology. The metrology system is a micromachined scanning interferometer having a sub-nm resolution in a compact design. The proposed microinterferometer forms a phase sensitive diffraction grating with interferometric sensitivity, while adding the capability of better lateral resolution by focusing the laser to a smaller spot size. A detailed diffraction model of the microinterferometer was developed to simulate the device performance and to suggest the location of photo detectors for integrated optoelectronics. A particular device is fabricated on a fused silica substrate using aluminum to form the deformable diffraction grating fingers and AZ P4620 photo resist (PR) for the microlens. The details of the fabrication processes are presented. The structure also enables optoelectronics to be integrated so that the interferometer with photo detectors can fit in an area that is 1mm x 1mm. The scanning results using a fixed grating micromachined scanning interferometer demonstrated that it could measure vibration profile as well as static vertical(less than a half wave length) and lateral dimension of MEMS. The SI, which is integrated with photo diodes, demonstrated its operation by scanning a cMUT. The PID control has been tested and resulted in improvement in scanned images. The integrated micromachined scanning interferometer demonstrated that the deformable grating could be used to tune the measurement keep the interferometer in quadrature for highest sensitivity.