Proceedings Article | 12 October 2021
KEYWORDS: Photomasks, Semiconducting wafers, Inspection, Reticles, Lithography, Manufacturing, Critical dimension metrology, Computer simulations, Wafer-level optics, SRAF
Comprehensive disposition of reticle defects is critical for process and yield control. Misjudging a real defect on mask may not only reduce its lithography process window but also kill thousands of wafers causing unbearable economic loss. With the development of OPC and ILT technology, manual judgement of reticle defects has become more challenging. The situation is even worse in advanced logic fab, especially for foundry, where pattern complexity and diversity vary from worldwide fabless upstream firms. Working with KLA, USCXM adopted and reported ADC (Automated Defect Classification) and DPM (Defect Progressing Monitor) solutions to avoid defect misclassification and to alarm defects degrading [1]. These solutions run smoothly and shorten the cycle time in daily routine production. However, both functions cannot well predict the defect printability on wafer when there are questionable mask defects. Usually, the problematic mask has to be sent back to mask shop, where an AIMSTM tool evaluates printing risk, leading to a very time-consuming verification cycle. Thus, a cutting-edge technology called LPR (Lithography Printability Review) has been fully qualified and applied in a logic foundry for the first time. Using the optical mask inspection images, with LPR, the aerial image CD error can be accurately modeled thereby eliminating possibility of any related yield loss, while also dramatically shortening the cycle time for verifying such defects. In this paper, we introduce a series of strict qualification processes for LPR adoption. The qualification flow involves both PDM (Programmed Defect Mask) and production mask with respective purpose. The PDM verification covers various defect types while the production mask provides abundant pattern geometry. The LPR vs AIMSTM simulation efficiency is over 90% without missing one killer defect. Furthermore, LPR operates as part of an integrated solution with ADC and DPM. Typical production cases are also presented in this paper to demonstrate its invaluable contribution to avoiding yield loss. The RA (Reticle Analyzer) product including ADC, DPM and LPR, is the only mature solution, and is now deployed in full volume mask manufacturing production, driving intelligent automation with zero misoperation, shortened cycle time, and increased fab productivity.
