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Evaluation and characterization of flare in ArF lithography

The impact of flare on lithographic imaging has been the subject of increased investigation as critical dimension requirements and K1 factors continue to be reduced. All 'real world' lithographic systems include aberrations and non-uniformities that detract from the ability to produce the ultimate imaging possible. The increased acceptance of double exposure techniques, such as complementary phase shift, can greatly increase the sensitivities of the process by effectively doubling the flare exposure in each image. All optical imaging systems have some amount of stray light, or flare, that detracts from system performance, critical dimension (CD) control, and process latitude. The effects of flare are compounded with the use of multiple exposure processes are used since this doubles the amount of exposure energy going through the optics and therefore increase the amount of stray light. Flare was characterized on two 0.63NA 193nm lithographic scanners using two different measurement techniques. Using a double-exposure technique previously presented new data that characterizes the across slit flare performance of a 193nm lithography system is reported. Data showing the effect of lens contamination and cleaning is also presented. In addition, a different flare metrology technique based on MTF was used to characterize the flare effects at a range of spatial frequencies. Metrology requirements and limitations of each technique are also discussed.