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Specification of the phase angle of a 6% attenuated PSM mask used in ArF lithography

As 6% attenuated phase shift masks (PSM) become commonly used in ArF advanced lithography for the 90nm Technology and mass production to print lines/ spaces as well as contacts, the specification and control of the phase angle and the width of the distribution of phase angles becomes critical to maintain the quality of the lithography process. The influence of the mean phase angle and the width of the distribution of phase angles on the best focus, the through pitch behavior and uniformity of the critical dimension (CD uniformity) has been studied experimentally using a 6% attenuated PSM whose phase angle has been affected by several reticle cleans. The results are consistent with aerial image simulations. Independent specifications for the mean phase angle and the width of the distribution of phase angles have been derived and could be applied for the production of masks in the future.