Throughput vs. Yield: reviewing the metrology needs for stochastics-aware process window analysis (SA-PWA)
In the past decade, EUV lithography has rapidly evolved, and has finally been acknowledged as a requirement for continued scaling. While there have been many improvements on the scanner side to improve resolution, throughput and performance, metrology and characterization have also played a significant role in enabling process maturity and yield. Now, an EUV process owner's toolbox contains infrastructure and methodology for stochastics-aware process window analysis (SA-PWA), and the subsequent data is a keystone for process transfer to high-volume manufacturing (HVM). However, the monitoring, metrology and analysis needed for SA-PWA is oftentimes at odds with the throughput metrics for HVM. At first, methods for detecting stochastic failures were developed by pushing existing tooling, such as critical dimension scanning electron microscopy (CDSEM), e-beam inspection (EBI) and Brightfield inspection (BFI), outside of its comfort zone to find these nanosized defects at sub-36nm pitch. On one hand, application of these methods improved yield at aggressive sub-36nm pitches. On the other hand, inspections are on the order of hours per wafer or days and the data requires rigorous manual analysis. There are some compromises to improve SA-PWA without sacrificing improvements to yield, but eventually throughput will plateau and become the rate-limiting step in an EUV process development cycle. Continued improvement requires innovative development of next-generation metrology tooling and software components for data analysis, and simplified, or better yet automated, SA-PWA.