Extreme ultraviolet lithography (EUVL) has been selected to print a new generation of semiconductor chips at the 22 nm half-pitch node and beyond [1]. This technology has been demonstrated at laboratory and beta-tool scales but several technological issues, including the fabrication of defect-free masks, need to be addressed before it can be implemented for mass production of chips. In support of EUVL, there is a need to develop metrology tools capable of detecting printable defects on masks and mask-blanks. The most reliable way of detecting printable defects is to image the Mo/Si coated mask at the wavelength employed in the printing process, 13.5 nm. This is key to detect absorption contrast defects in the surface of the mask as well as phase defects generated from imperfections within the layers of the resonant-reflective multilayer coating. Demonstrations of high resolution actinic aerial microscopes have until now been conducted at synchrotron facilities where 13.5 nm wavelength radiation from bending magnets provides the required illumination [2-4]. Transitioning EUV inspection microscopes into compact devices to inspect EUVL masks on-site is possible but requires table-top light sources with high brightness and sufficient flux near 13.5 nm as found in recently developed EUV lasers. [5-7].
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