Phase Defect Observation Using Extreme Ultraviolet Microscope

Abstract

An aerial image mask inspection system for extreme ultraviolet lithography (EUVL) is developed. This system consists of microscopes using the same wavelength of light as is used for the exposure and produces a magnified image of defects on a mask. Using this microscope, amplitude defects on finished masks and phase defects on glass substrates are observed. A phase defect was formed by a multilayer coated on a line pattern with 5 nm high and 90 nm wide on a glass substrate. Although the defect detected is made beforehand, it is detected by reflection of the light which penetrated the multilayer. These results show that it is possible to detect the internal reflectivity distribution without depending on surface perturbations. We tried to observe "pit defects", but it was not possible to observe these at this time. The pit defects, such as scratches on glass substrates may not become defects depending on the process of formation of the multilayer.