As the semiconductor industry advances to ever-smaller nodes with finer feature sizes and more complex mask designs, reticle quality and reticle defects continue to be a top mask yield risk. The primary reticle defect quality requirement is defined as “no reticle defects causing 10% or larger CD error on wafer”. Beginning at around the 7 nm Logic node, EUV lithography will start pilot production in several leading fabs. EUV masks stress reticle defectivity requirements for mask shops even more than optical masks due to the larger printing impact from a similar size defect on the mask, and the greater cost and longer cycle time for EUV masks. In a mask shop, generally there are three use cases for a blank inspection system, which are used to monitor and improve mask defectivity; 1) Inspecting process monitor masks, which are used to partition the mask process and identify defect excursions, 2) inspecting ‘witness’ blanks, which are used to measure and control defectivity in each process tool / chamber and 3) inspecting incoming mask blanks to ensure defect-free starting materials for advanced optical and EUV reticles. Traditionally, mask shops have been using bright field confocal technology to perform these tasks. However, due to more stringent defect requirements and the flexibility necessary to support these varied use cases, the industry requires a new approach to drive yield improvements in mask manufacturing. In this paper, we report on the introduction of a new system that provides superior sensitivity, with very high throughput and the flexibility to adapt to many different use cases in a production environment.
Advanced Inverse Lithography Technology (ILT) can result in mask post-OPC databases with very small address units, all-angle figures, and very high vertex counts. This creates mask inspection issues for existing mask inspection database rendering. These issues include: large data volumes, low transfer rate, long data preparation times, slow inspection throughput, and marginal rendering accuracy leading to high false detections. This paper demonstrates the application of a new rendering method including a new OASIS-like mask inspection format, new high-speed rendering algorithms, and related hardware to meet the inspection challenges posed by Advanced ILT masks.