Linewidth asymmetry study to predict aberration in lithographic lenses

In low-k1 optical lithography, aberration effects are more significant than ever before. Typically, aberrations are measured by phase measuring interferometry (PMI) when the lenses are fabricated, but this technique is not accessible for lithographers, nor does it include resist effects. Recent progress in resist-based evaluation techniques makes reliable Zernike coefficients available in many cases, but these approaches are still far away from practical application for lithographers, because it remains necessary to know which Zernike coefficients are important for controlling CD variations in each application. It is well known that coma aberration causes local CD variation, which is critical for device performance. In this study, we investigated in detail, characteristics of coma-induced linewidth asymmetry. From a practical point of view, the characterization methods proposed here could be used either for classification of lenses or to specify IC design rules.