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The use of higher NA lenses of next generation 248 nm microlithography systems sets tight requirements on the spectral purity of the laser, especially because these lenses are not chromatically corrected. Present day KrF excimer lasers are equipped with etalon-based spectrometers that can measure the laser linewidth at full-width-at-half-maximum (&FWHM), at nearly every pulse. Both, experience and analysis have shown that the AX FWHM may not be the optimum measure of laser spectral purity, and that a better characterization would be the width of the line that contains 95% ofthe laser energy, AX iflt Therefore, the lithographer is at risk of losing the image quality if the line shape, characterized by is outside its limit, even if the laser signals that the AXFW is within limits. In this paper, we describe the results of our development of new generation spectrometers that are capable of making simultaneous, high resolution AX FWHM and L\X95% measurements of laser line shape. The measurements can be done on a pulse-to-pulse basis or with averaging over an exposure window. Several different configurations and their comparable analysis are presented. These new spectrometers are compact, and can be integrated with a deep UV laser or used as a portable field service tool. Despite the small size, the spectrometers have a resolution of about 0. 1 pm when measuring FWHM values and about 0.3 pm when measuring 95% integral values. The implementation of these new metrology tools provides the lithographer with a correct measure of the laser spectral purity during exposure and during process optimization.

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-AtHalf-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 tools should be either portable or built into the laser. They should be able to provide contmuos 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.

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