Evaluation of EUVL-mask pattern defect inspection using 199-nm inspection optics

摘要

In this paper, we will report two evaluation results. One is the relationship between EUVL mask structure and image contrast values captured by 199nm inspection optics. The other is the influence of mask structure on defect inspection sensitivity. We utilized a commercially available DUV inspection system that has the shortest inspection wavelength at 199nm. Using the 199nm inspection optics, enough image contrast values on hp32nm 1:1 lines and spaces using ArF-half tone (HT) mask were obtained. On the other hand, image contrast values were not sufficient for conventional EUVL mask that have a 70nm absorber layer thickness. To improve the contrast values of mask pattern image, we evaluated the effect of absorber layer thickness on inspection image contrasts. As a result, reducing the thickness of the absorber layer to 44nm, enough image contrast values of hp32nm 1:1 lines and spaces patterns were obtained. In this paper, the influence of the thickness of absorber layer on inspection sensitivities for opaque and clear extension defects are also discussed.