Multi-degree of Freedom Optical Metrology Techniques
Xiangzhi Yu, Ph. D. Defense
Wednesday, November 30, 2016
Precision linear stages provide the basic movement for many nanotechnology systems such as lithography stages, biological scanning systems, and nanofabrication positioning systems. All these systems require precise position sensing for feedback control and extensive calibration procedures to achieve the required accuracy. This thesis begins with proposing and experimentally validating an analytical model for analyzing beam geometry, system alignment, and wavefront aberration effects on using a Differential Wavefront Sensing technique, which serves as the working principle for the simultaneous measurement of displacement, pitch, and yaw. Afterward, a compact state-of-the-art six degree-of-freedom optical metrology system is presented which enables fast, accurate calibration and error mapping of all the geometric errors simultaneously. The working principle for each degree-of-freedom measurement is presented and system-level integration is investigated to evaluate the overall performance. Lastly, a refractometer based on variable length vacuum cell which enables both absolute refractive index of air sensing and tracking is presented, which is suitable for real-time compensation of ultra-precision interferometry measurements under atmospheric conditions.