Model-free and model-based methods for dimensional metrology during the lifetime of a product

For future technology nodes, highly accurate dimensional metrology will become more and more important. At this stage, measuring layer thickness in planar test structures or geometrical dimensions in simplified proxy structures may be not sufficient for accurate control of highly sophisticated process steps. Model-based dimensional metrology has the potential to provide critical parameters of interest for process control in high volume manufacturing, while during process and technology development the constrained flexibility of models and the required model-building efforts may be a serious limitation. On the other hand, model-free dimensional metrology may provide sufficient flexibility for process development, while in some cases it may not be production-worthy in high volume manufacturing. This article details advantages and disadvantages of the different methods during the lifetime of a product starting from early development to high-volume production.