Combined absorber stack for optimization of the EUVL mask

摘要

Integration and optimization of the absorber stack has become a critical issue with the progress of the extreme ultraviolet lithography development because it influences many issues such as throughput, pattern fidelity, and mask yield. Simulation works to optimize an absorber stack were carried out and the results were empirically confirmed. TaN showed a great potential as an extreme ultraviolet absorber property but it did not meet the requirement for deep ultraviolet reflectivity for inspection. According to the simulation, Al_2O_3 was selected as an anti-reflection coating for DUV wavelength. Al_2O_3 ARC with optimum thickness reduces the DUV reflectivity from 42.5 to 4.4 % at 248 nm while maintaining the other properties. A novel absorber stack consisted of TaN absorber, Ru capping, and Al_2O_3 ARC is proposed, and the total thickness of the stack is only 47 nm and the EUV and DUV reflectivities are 0.97% at 13.5 nm and 4.4% at 248 nm, respectively.