Development of highly spatial-coherent, 13.5-nm high-order harmonics for EUVL mask inspection using coherent EUV scatterometry microscope

We demonstrate the generation of low divergence, spatially coherent, high-order harmonics (orders ranging from 23rd to 95th) using commercial sub-TW laser system. The 6 mJ, 32 fs laser pulses were loosely focused with f/125 concave mirror in a semi-infinite gas cell. The beam divergence was measured to be 0.18-mrad at the 59th harmonics (13.5 nm) in 18kPa of helium. The 59th harmonics with novel high-throughput, spatial beam separator, which has attenuation ratio of 0.01 for the pump pulse, was used to detect line-defects in extreme-ultraviolet lithography mask. A 2nm-wide line-defect in an 88-nm line-and-space pattern was successfully detected using diffraction imaging technique.