High-precision and cost-effective EUV reticle defect registration with integrated grid matching using KLA LMS IPRO and FlashScan

In this paper we introduce a method of combining the use of the KLA FlashScan® reticle blank defect inspection system and the KLA LMS IPRO reticle pattern registration metrology system for high-precision mask defect inspection and registration. We investigated EUV mask blanks at various production stages and confirmed the reliable measurement of defect coordinates, which propagate through the multilayer stack towards the surface as well as after the absorber deposition process. During the inspection, in addition to the categorization among various types and sizes of blank defects, unique alignment marks were also placed on the mask. These alignment marks allowed us to use a defined coordinate system, enabling reliable and accurate registration of the defect location even on blank substrates. If the mask shop requires EUV defect coordinates in their own internal coordinate system, matching between the mask shop and blank coordinate systems is achieved by measuring both alignment mark pairs and applying the appropriate coordinate transformation. The combined use of inspection and metrology systems proved to be a cost-effective solution for the development of a defect mitigation strategy with automatic workflow for EUV mask shops and mask blank suppliers.