Mirau interferometer

Abstract: Conventional surface-characterization techniques either are not sophisticated enough to provide complete surface-topographical data or cannot be employed because of the relatively low hardness of magnetic media. An optical profilometer has been developed which provides a noncontact method of obtaining surface characteristics from a magnetic medium. The system consists of a standard Leitz reflection microscope, a Mirau interferometer controlled by a piezoelectric transducer, a linear array of photodiode detectors, and a microcomputer. The combination yields a system that measures the optical-height variations of surfaces to a high degree of precision. This height variation is processed by a computer to provide surface-topographical statistical parameters, which are useful to predict tribological and magnetic performances of the head-media interface. Sample data of magnetic media (tape, floppy disk, and rigid disk) are presented. Presented at the 38th Annual Meeting in Houston, Texas, April 24–28, 1983

Abstract: We propose a polarization Mirau interferometer using the pixelated polarization camera to acquire the four phase-shifted interferograms simultaneously by which motionless phase shift can be realized. A wire-grid polarizer is employed as the polarization beam splitter to realize the adjustable fringe contrast. Due to the limited contrast ratio of split orthogonally polarized beams with a wire grid polarizer, the corresponding calibration method by superposition of exchanged transmitted and reflected beams is proposed to obtain the uniform fringe contrast in four phase-shifted interferograms. The accuracy of the proposed system is demonstrated experimentally, and a precision better than 1/500 wavelength is achieved. The proposed system provides a feasible way to obtain the instantaneous measurement with minimizing environmental disturbance.

Abstract: We present the development of an array type of micromachined Mirau interferometers, operating in the regime of low coherence interferometry (LCI) and adapted for massively parallel inspection of MEMS. The system is a combination of free-space micro-optical technologies and silicon micromachining, based on the vertical assembly of two glass wafers. The probing wafer carries an array of refractive microlenses, diffractive gratings to correct chromatic and spherical aberrations and reference micro-mirrors. The semitransparent beam splitter plate is based on the deposition of a dielectric multilayer, sandwiched between two glass wafers. The interferometer matrix is the key element of a novel inspection system aimed to perform parallel inspection of MEMS. The fabricated demonstrator, including 5 × 5 channels, allows consequently decreasing the measurement time by a factor of 25. In the following, the details of fabrication processes of the micro-optical components and their assembly are described. The feasibility of the LCI is demonstrated for the measurement of a wafer of MEMS sensors.