Absolute evaluation of out-of-band radiation from laser-produced tin plasmas for extreme ultraviolet lithography

Out-of-band (OOB) radiation (at wavelengths longer than 130nm) from an extreme ultraviolet (EUV) light source reduces the precision of lithography. The energy of the OOB radiation from laser-produced Sn plasmas were measured by using an absolutely calibrated transmission grating spectrometer equipped with a charge-coupled device. The dependence of the OOB radiant energy on the mass and size of the tin fuel was clarified. The dominant source of the OOB radiation is peripheral heating around the laser spot via electron thermal conduction and radiation from the high-temperature EUV emission region.

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