Phase Shift Improvement in ArF/KrF Haze-free Mask Cleaning

摘要

The continuous evolution of LSI design rules has created an increased demand for the use of KrF and ArFphase-shift photomasks (EPSMs). One of the critical issues in the use of those photomasks, especially ArF half-tonephotomasks, has been the generation of optical hazes known as (NH_4)_2SO_4. The other critical issue has been a relativelylarge phase shift of those ArF and KrF photomasks caused by so-called haze-free mask cleaning.. In the present study we used an SPM integrated clean (as a reference) consisting of heated SPM, diluted SC-1 andheated UPW (widely known for rinsing), and a haze-free integrated mask clean consisting of Ozonated-water with asimultaneous 222nm Excimer UV irradiation, diluted SC-1 and heated UPW. We found that both Ozonated-water with asimultaneous 222nm Excimer UV irradiation and the diluted SC-1 (the components of the haze-free integrated clean)caused a sizable phase shift during the mask clean. We also found that the other component of the haze-free integratedclean, the heated UPW developed a relatively large phase shift in those photomasks. We have confirmed that the morewe repeat the use of the 172nm Excimer UV light irradiation treatment before the clean, the less (more improved) phaseshift has been realized in the haze-free clean. We found that the haze-free integrated clean also developed the CD shiftsof the above photomasks and that those CD shifts could be recovered (reduced) drastically by the use of the 172nmExcimer UV light irradiation before the clean.