Development of standalone coherent EUV scatterometry microscope with high-harmonic-generation EUV source

Abstract

For extreme ultraviolet (EUV) mask evaluation, we have developed the coherent EUV scatterometry microscope (CSM), which is equipped with a laboratory coherent EUV source for high-harmonic generation (HHG) and acts as a standalone EUV tool. The CSM records the diffraction from mask patterns directly with a charge-coupled-device (CCD) camera, which was illuminated with the coherent EUV light. The pattern image and the critical dimension values are evaluated by using the diffraction image with iterative calculations based on coherent diffraction imaging. The 59th high-order harmonic generation at a wavelength of 13.5 nm was pumped by a tabletop 6 mJ, 32 fs, Ti:sapphire laser system. EUV output energy of 1 μW was successfully achieved. We observed the EUV mask using the HHG-CSM system. A very small 2 nm-wide line defect was successfully detected while located in an 88 nm line-and-space pattern.