Comparison of Actinic Lens Characterization by Arial Image Evaluation and Interferometric Testing for 157nm high-NA Micro-Objectives

摘要

Focusing on smaller features for optical inspection or damage repair, smaller wavelenths are used to increase resolution or energy density. Objectives designed for 157nm will use calcium fluoride optics and the objectives need to be evaluated and optimized actinic, at wavelength. Measurement set-up and imaging results are presented through a catadioptric type of micro-objective. The set-ups and measurements are done at the 157nm wavelength as to include all actinic material effects. The imaging set-up uses a custom illuminator to image 130nm features, 500 times enlarged, onto a back-thinned CCD camera in real time. The knowledge of the spatial coherence characteristics of the light source together with the through-focus imaging of structures at various angles allows for the reconstruction of the wave aberrations of the lens. The lens is also measured and optimized using an interferometric set-up and phase shifting techniques.