The availability of defect-free masks is considered to be a critical issue for enabling extreme ultraviolet lithography (EUVL) as the next generation technology. Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of EUV mask defects. In this work, two native mask blank defects were characterized using atomic force microscopy (AFM) and cross-section transmission electron microscopy (TEM), and the defect printability of the characterized native mask defects was evaluated using simulations implementing the finitedifference time-domain and the waveguide algorithms. The simulation results were compared with through-focus aerial images obtained at the SEMATECH Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory. The authors found agreement between the through-focus simulation results and the AIT results. To model the Mo/Si multilayer growth over the native defects, which served as the input for the defect printability simulations, a level-set technique was used to predict the evolution of the multilayer disruption over the defect. Unlike other models that assume a constant flux of atoms (of materials to be deposited) coming from a single direction, this model took into account the direction and incident fluxes of the materials to be deposited, as well as the rotation of the mask substrate, to accurately simulate the actual deposition conditions existing inside the ion beam deposition tool. The modeled multilayer growth was compared to the cross-section TEM images through the defects, as well as to the AFM scans for the given defects, and a good agreement was observed between them.
Since completely defect-free masks will be hard to achieve, it is essential to have a good understanding of the printability of the native extreme ultraviolet (EUV) mask defects. In this work, we performed a systematic study of native mask defects to understand the defect printability they cause. The multilayer growth over native substrate mask blank defects was correlated to the multilayer growth over regular-shaped defects having similar profiles in terms of their width and height. To model the multilayer growth over the defects, a multilayer growth model based on a level-set technique was used that took into account the tool deposition conditions of the Veeco Nexus ion beam deposition tool. Further, the printability of the characterized native defects was studied at the SEMATECH-Berkeley Actinic Inspection Tool (AIT), an EUV mask-imaging microscope at Lawrence Berkeley National Laboratory. Printability of the modeled regular-shaped defects, which were propagated up the multilayer stack using level-set growth model, was studied using defect printability simulations implementing the waveguide algorithm. Good comparison was observed between AIT and the simulation results, thus demonstrating that multilayer growth over a defect is primarily a function of a defect's width and height, irrespective of its shape.
Articles you may be interested inResidual-type mask defect printability for extreme ultraviolet lithography J. Vac. Sci. Technol. B 30, 06F501 (2012); 10.1116/1.4756934The effects of oxygen plasma on the chemical composition and morphology of the Ru capping layer of the extreme ultraviolet mask blanks Cleaning of extreme ultraviolet lithography optics and masks using 13.5 nm and 172 nm radiation It is widely recognized in the semiconductor industry that getting to defect-free extreme ultraviolet (EUV) mask blanks is critical in achieving high volume chip manufacturing yield beyond the 22 nm half-pitch node. Finished mask blanks are normally subjected to a cleaning process to get rid of the loosely adhered particles on the top. It is important that this cleaning process does not degrade the properties of the multilayer blank or introduce additional particles or pits during the process. However, standard cleaning processes used to clean multilayer blanks can result in EUV reflectivity loss, loss of uniformity in reflectivity, increased roughness, and add pits and particles on mask blanks. The standard cleaning process consists of multiple steps, each of which may cause the oxidation of the ruthenium capping layer, as well as the underlying bilayers, etching of the multilayer stack, and increased roughness of the bilayers, thus leading to a loss in EUV reflectivity. It is a challenging task to experimentally correlate the processing steps to the resulting damage and to quantify the reflectivity loss. Further, due to the high cost of materials we have not been able to perform extensive experiments to determine the root cause of problems. In this work, we have combined mask blank cleaning using standard processes, x-ray photoelectron spectroscopy, transmission electron microscope cross section, and atomic force microscope studies with simulations to quantify the impact of the multilayer oxidation, etching, and roughness on the EUV reflectivity loss and mask blank degradation.
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