Influence of laser spatial parameters and illuminator pupil-fill performance on the lithographic performance of a scanner

摘要

Litho-tool illuminator performance, characterized by quantitative measurements of pupil-fill intensity distribution and cross-field uniformity, has been cited as a key contributor to CD uniformity. While both modeling exercises with simulated pupil fills and measurements of real pupil fills have been undertaken, quantitative assessments of the pupil's effect when compared with other CD error contributors are rare. An integral part of illuminator performance is, of course, the laser. Not only must a litho laser meet stringent requirements at installation, but also the litho tool and laser suppliers are responsible for ensuring performance after maintenance activity, such as laser module replacement. We have investigated the effects of adjustable spatial laser parameters on the illuminator pupil fill as measured via a pinhole reticle and on illumination uniformity as measured by the scanner. We present the experimental results of these studies, estimates of their effects on litho performance via modeling, the sensitivity of lithographic performance to the spatial parameters, and an assessment of their importance relative to other lithographic variables affecting CD uniformity. Results show that not only is the baseline illuminator pupil-fill performance a small contributor to lithographic error, but also that the system is stable in the presence of laser adjustments.