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Material limitations to 193-nm lithographic system lifetimes

Several experiments are reported to better predict the 193-nm radiation-induced compaction rates of fused silica at lithographic intensities. Birefringence monitoring is capable of measuring the compaction-induced birefringence distribution from modest total fluences. For example, 6 hours at 350Hz with a per pulse energy density of only 1.1mJ/cm2 produces a relative compaction of about 38 ppB and corresponding relative refractive index change of 11 ppB which is easily measured. Moreover, this value of compaction is more than would be predicted by extrapolation from past higher fluence experiments. Compaction follows a non- linear dependence on pulse count. Compaction rates drop with continuing irradiation but do not saturate in the 1-10 ppm compaction range. The dependence of compaction on intensity is found to accurately follow an intensity squared rule that is all data over a wide range of pulse energy densities can be plotted via a single curve. Using this result, one can now scale higher energy density tests to predict damage rates of materials at lower fluences. Although compaction rates can vary by a factor of three over all sample types, we find less than 25 percent variation in compaction rate among UV grade samples.