Characterization of DUV and VUV optical components

In order to improve the efficiency of optical components for microlithography, metrology for comprehensive characterization of DUV and VUV radiation and the related optics has been developed at Laser-Laboratorium Gottingen. The performance of optical components is assessed by measuring absorptance, scatter losses and damage thresholds during ArF and F-2 laser irradiation. Absolute linear and non-linear absorption coefficients are determined by high-resolution laser calorimetry, which provides greatly enhanced accuracy as compared to transmissive measurements. This technique accomplishes also fast monitoring of laser induced degradation phenomena. The absorptance data are compared with the results of accompanying high-resolution laser-induced fluorescence measurements. For an assessment of the optical quality of DUV/VUV optics, a specially designed wavefront analyzer based on the Hartmann-Shack principle is employed. This device, which also allows accurate beam characterization of ArF and F-2 laser in the near- and far-field, can be used as an alternative to interferometric measurements for 'at wavelength' testing of optics, e.g. for on-line monitoring of compaction or lens heating in fused silica.