Pattern Inspection performance of Novel Projection Electron Microscopy (PEM) on EUV masks

EUV lithography with 13.5 nm exposure wavelength, because of its excellent resolution, is a leading candidate for the next-generation lithography for 16 nm half pitch (hp) node devices, and beyond. High-sensitivity EUV mask pattern defect detection is one of the major issues to realize device fabrication with EUV lithography. In order to achieve inspection sensitivity and attainability for 1X node, a projection electron microscopy (PEM) system is employed that enables us to do high-speed/high-resolution inspection that is not possible with the conventional DUV or EB inspection systems. By selecting a higher electron energy in imaging by using Electron Optics (EO) exposure, and by applying a newly designed model to a basic PEM optics model, we have minimized the aberration in imaging that occurs when working with EO; and we have improved the related transmittance of such a system. Experimental results by showing designs for the improved transmittance were obtained by making electron throughput measurement. To guarantee the quality of the 16 nm node EUV mask, corresponding sized programmed defects on masks were designed, and a PEM system for defect detection was evaluated by using the developed EO.