Exploring and Extending the Limits of CD-SEMs' Resolution
Andras Vladar, Michael T. Postek, John S. Villarrubia
This study of SEM resolution is occasioned by concerns that it is no longer adequate for lithography process control in integrated circuit manufacturing. For example, according to the most recent International Technology Roadmap for Semiconductors, the in-line nondestructive microscopy resolution requirement is shown as red (manufacturable solutions are not known) for now and the foreseeable future. Questions naturally arise: Does today's SEM performance represent a fundamental limit? Or could better instrument or measurement design improve performance? To the end of better instrument and measurement design, what are the major factors that influence or limit resolution performance' These conclusions reveal that the spatial and measurement resolution are not the same, the latter can be better by a factor of 10. There are possible improvements to current CD-SEMs, like optimizing and monitoring the spatial resolution and noise performance of the instruments. The optimal choice of measurement algorithms is essential, for example, sigmoidal fit worked best (after model-based) in this study. Users must be aware that measurement biases play a heretofore largely unsuspected role in degrading measurement resolution; fortunately, it is possible to compensate for them. Further improvements can be implemented only on new designs, like the use of optimized data collection system, and new edge algorithms, which exploit all information in the collected: data. It is expected that the results of this study will help to extend the usefulness of SEM metrology for process control and lead to more conscious and optimized CD SEM measurements: collection of the right kind and right amount of data, not more, not less. Our conclusions point to the lack of optimization in measurement algorithms and in the instrument''s signal chain.
Final report to International SEMATECH
edge algorithm, field emission gun, resolution, scanning electron microscope, SEM