Laser spectrum line shape metrology at 193 nm

The spectral shape requirements for an ArF laser for 193nm microlithography are expected to be about 2X tighter than at 248nm. This is in part due to the dispersion of fused silica and CaF2 at 193nm and in part due to the push by the lens designers towards higher NA lenses. However, unlike 248nm, it is likely that the process engineer may not be satisfied with simple spectral bandwidth measurements of Full-Width-At-Half-Maximum (FWHM). Instead, the knowledge of the complete spectral shape may be required, since it is the total shape that has an impact on the lens performance. This requirement may have significant impact on corresponding metrology tools. These toots should be either portable or built into the laser. They should be able to provide continuos feedback to the process engineer as far as the lens performance is considered. Present paper discusses recent developments in 193 nm metrology which can be implemented as a part of laser on-board diagnostics or as a field service tool, and is capable of accurately measuring the laser spectrum shape. This information, together with proprietary lens parameters, will allow process engineer to accurately evaluate the aberrations due to the laser line shape.