Table-top microscope for at-wavelength inspection of extreme ultraviolet lithography mask

Extreme ultraviolet lithography (EUVL) has been selected to print a new generation of semiconductor chips at the 22 nm half-pitch node and beyond. 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.