Enabling accurate and cost-effective registration metrology on EUVL masks

As EUV lithography moves towards high-volume manufacturing, standardized commercial EUV masks are becoming available. The overlay requirements for the technology nodes utilizing EUV lithography are very tight, therefore reliable and accurate reticle registration metrology—on target and especially on-device areas—is of great importance. We report investigations using the latest generation LMS IPRO system for reticle pattern placement measurements on EUV masks. High performance metrology is based on excellent optical imaging capabilities and consideration of the reticle optical properties for EUV mask-specific measurement setup. This enables highaccuracy, model-based measurement on the device. The die-to-database algorithm is optimized with respect to the mask pattern properties of EUV masks. Repeatability and accuracy results are presented. The cost effectiveness of LMS IPRO is demonstrated by comparing results of high-performance and high-throughput modes.