Experimental investigation of the mask diffraction light blocking with critical-sized Sn particles on the EUV pellicle

Abstract

Recently, chip makers have selectively adopted the EUV pellicle to mitigate yield reduction caused by the particle issue originating from the Sn droplets of a laser-produced plasma source. However, other research groups have proposed the critical size of particles based on simulated data with illumination pupil control, underscoring the necessity of experimental investigation using an optical system that emulates that of an EUV scanner. In this study, we demonstrate the effect of a particle on the pellicle on diffracted light shape and investigate its impact on mask imaging performance. This investigation was conducted through pellicle imaging using Sn particle-patterned pellicles and a coherent scattering microscope, which is an actinic inspection tool that uses a coherent harmonic source. As a result, we confirmed that the light intensity decreased to 4.031%, and the scattered light spread up to 146.01% when a 10 µm-sized particle on the pellicle blocked a specific mask diffraction order. To study this particle's effect on mask imaging performance, pattern images were reconstructed from particle-affected diffraction patterns using a phase retrieval algorithm. Eventually, a critical dimension variation of 51.15 nm and a pattern shift of 48.57 nm were confirmed with a 200 nm critical dimension of the mask pattern, as a result of particle-induced spatial frequency and phase variation. Therefore, the critical defect size of the pellicle should be determined based on the most severe lithographic variations resulting from the mask diffraction light blocked by the particles.