Reflectance Improvement of Mo/Si Multilayer Mirrors and Masks for Extreme Ultra-Violet Lithography

• Main Authors: Fang-Yi Liu, 劉芳宜
• Other Authors: Yang-Tung Huang
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/77100946056740022341

碩士 === 國立交通大學 === 加速器光源科技與應用碩士學位學程 === 100 === In this study, the design and characteristics of Mo/Si multilayers for extreme ultra-violet (EUV) lithography have been investigated. The reflectance of the quarter-wavelength multilayers can be enhanced further by optimized procedures with which the layer thicknesses are varied for best performance. For commercial EUV lithographic systems multilayer mirrors and masks require with higher reflectance and better stability. Interface-engineered Mo/Si multilayers with 72.62% reflectance and a FWHM of 0.828 nm at 13.5-nm wavelength have been developed and simulated. The design was achieved with 54 pairs of Ru/Mo/B4C/Si multilayer. This structure consist of alternating Mo and Si layers separated by thin boron carbide (B4C) and ruthenium (Ru) layers. Ru barrier layer was inserted into a Mo-on-Si interface and B4C barrier layer was inserted into a Si-on-Mo interface to improve the EUV reflective multilayer properties. About 4 % improvement of the reflectance at 13.5-nm wavelength compared to standard quarter-wave stacks can be acquired by the design. The best results according to simulation were obtained with 1.4-nm-thick Ru layers for the Mo-on-Si interfaces and 0.2-nm-thick B4C layers for the Si-on-Mo interfaces. The contaminations of optical surfaces by photon irradiation in the presence shorten optics lifetime become one of the main concerns. From simulation results, the most promising candidate seems to be Ru. The improvement in oxidation resistance of EUV multilayers has been achieved with Ru -capped interface-engineered Mo/Si multilayers. This structure achieves high reflectance and the great oxidation resistance during the EUV exposure in a water-vapor (oxidized) environment. Based on simulation results, we calculated reflectance for the reflective multilayer mirrors in a EUVL procedure and concluded that Ru-capped Ru/Mo/B4C/Si multilayers have a higher performance than quarter-wave Mo/Si multilayers. The simulation results clearly show reflectance improvement of our designed structure compared with standard Mo/Si multilayer structures.