Laser assisted CD correction system for EUV masks is developed in order to satisfy the enhanced uniformity requirement for EUV layers. Based on the very nature of chemical reactions, the reaction rate between the EUV mask absorber and wet etchant is controlled to develop EUV mask CD correction system. The CD correction facility is developed by selective temperature control through local laser illumination including considerations on laser wavelength, beam size, position precision under wet etching solution environment, resulting in ultra-fine control of wet etch rate to obtain a process. The process developed is expected to play an important role in EUV productivity as it is the only technology that can respond to specification requiring extreme CD quality control of EUV masks.
With continued design shrinks enabled by EUV lithography, there is a greater need for high sensitivity reticle inspections to minimize defectivity during reticle manufacturing. While laser-illumination based inspection systems have been the workhorses in reticle quality control so far, electron-beam based inspection systems have fundamentally been expected to provide the highest resolution needed for the most critical layers. To address this EUV inspection need at the 3x nm pitch and beyond, KLA has developed a multi-column e-beam inspection system. This new e-beam inspector provides the industry’s highest sensitivity die-to-database inspection system and is based on a unique multi-column e-beam architecture for HVM-worthy throughput. With multiple systems shipped to address gap layers at leading-edge mask shops, this new system has demonstrated significant sensitivity advantages while overcoming the long-standing e-beam limitation of throughput gap vs. optical systems. This paper covers the technology that combines advantages of e-beam resolution with KLA’s database inspection algorithms. Additionally, recent inspection results are reviewed, highlighting the sensitivity results.
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.
It is now well established that extremely ultraviolet (EUV) mask multilayer roughness can lead to wafer-plane line-edge roughness (LER) in lithography tools. It is also evident that this same effect leads to sensor plane variability in inspection tools. This is true for both patterned mask and mask blank inspection. Here we evaluate mask roughness specifications explicitly from the actinic inspection perspective. The mask roughness requirement resulting from this analysis are consistent with previously described requirements based on lithographic LER. In addition to model-based analysis, we also consider the characterization of multilayer mask roughness and evaluate the validity of using atomic force microscopy (AFM) based measurements by direct comparison to EUV scatterometry measurements as well as aerial image measurements on a series of high quality EUV masks. The results demonstrate a significant discrepancy between AFM results and true EUV roughness as measured by actinic scattering.
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