INVESTIGATION ON ALIGNMENT SYSTEM FOR MULTILEVEL IMPRINT LITHOGRAPHY AND ITS AUTOFOCUS ALGORITHM

摘要

A precision alignment system based on video image is developed. The system hardware is mainly comprised of CCD cameras, microlens, video image card and precision positioning stage. The sub-pixel correlation template matching algorithm is adopted for alignment marks positioning and the system resolution of 0.2 m is obtained. The mark positioning error caused by defocus is identified through experiment and an auto-focusing method based on the analysis on the image information is investigated to improve the alignment accuracy. Several autofocus functions were evaluated concerning their applicability on the alignment mark images and the optimal one based on power in frequency domain is adopted and improved. The alignment error due to defocus can be reduced or eliminated by the auto-focusing implementation. The system is intended to accurately align the individual layers in layered fabrication of microstructures and can also be used as the coarse aligner for multilevel nanoimprint lithography (NIL) with higher overlay accuracy.