Overlay metrological system for overlaid linear gratings by an interferoscatterometer

Abstract

Interferoscatterometry is an optical measurement technology based on the analysis of light scattered and interfered from a periodic structure. In this work, first we build up a model for this system by the rigorous coupled wave analysis. With the model we calculate the diffractive efficiency of overlaid linear gratings with a mirror located in the incident region. Then, from the analyses of the overlaid linear gratings we obtain the best structure which has the highest sensitivity in the interferoscatterometry. Finally, we measure a sample and get experimental signatures. In order to get the overlay between the upper and lower grating, we compare the experimental signatures with theoretical signatures which are built in a library. The application of the interference technique on the scatterometry shows a higher sensitivity and a longer measurement range. (c) 2005 American Institute of Physics.