AIMS-45 image validation of contact hole patternsafter inverse lithography at NA 1.35

摘要

The AIMS~(TM)-45, when used in scanner mode, can emulate image intensity as seen in resist on the wafer at scannerillumination conditions. We show that this feature makes AIMS~(TM)-45 well-suited to analyze patterns treated withinverse lithography. We have used an inverse lithography technique by Mentor Graphics, to treat a random contact holelayout (drawn at minimal pitch 115nm) for imaging at NA 1.35. The combination of the dense 115nm pitch and availableNA of 1.35 makes Quasar illumination necessary, and the inverse lithography treatment automatically generated optimal(model-based) Assist Features (AF) for all geometries in the design. The mask, after inverse lithography treatment, hasCH patterns with numerous AF of different sizes and orientations, and is a challenge for both mask making and maskqualification. We have analyzed the inverse lithography masks with the model-based AF using an AIMSTm-45 aerial image measurement tool, and compare the results of the AIMS~(TM)-45 to wafer data obtained after exposure on an ASML XT:1900i. A first benefit of AIMS~(TM)-45 is that the most meaningful quantity (image in resist) is generated without theintermediate steps of doing multiple reticle SEM measurements followed by extensive simulation. A second point ofinterest is that the AIMS~(TM)-45 generates image intensities, which allows a direct validation of the intensity-driveninverse litho conversion. Both features prove the value of the AIMS~(TM)-45 for analyzing inverse litho masks andgeometries.