Enhanced reflectivity and stability of high-temperature LPP collector mirrors
Enhanced reflectivity and stability of high-temperature LPP collector mirrors
复制标题
增强高温 LPP 收集镜的反射率和稳定性
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
D. Brandt
中科院分区：
文献类型：
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作者：
T. Feigl;S. Yulin;M. Perske;H. Pauer;M. Schürmann;N. Kaiser;N. Böwering;O. Khodykin;I. Fomenkov;D. Brandt
光源输出功率和寿命，包括收集器光学器件寿命，是EUV光刻系统的关键问题之一。为了满足EUV收集器反射镜的要求，在最近的开发工作中，其多层涂层的反射率和长期热稳定性都得到了显著提高。在外径约320 mm的不同衬底材料的子孔径椭球镜上镀上横向梯度高温多层膜。界面工程Mo/Si多层膜反射镜（MLM）涂层在13.5 nm处具有高峰反射率，工作温度高于400°C。在两个界面上引入薄的阻挡层，以阻止钼和硅的热诱导相互扩散过程，并在高温下提供涂层的长期光学稳定性。在加热至600°C后，在Si晶片样品上测量到13.5 nm处的法向入射反射率R ~ 60%。在长期加热测试和多次退火循环过程中，这些多层涂层的光学性能没有发生退化。在具有改进的表面粗糙度的高度抛光的收集器基板上，获得了超过R = 57%的峰值的s偏振光的反射率。通过优化层梯度，波长匹配程度也得到了改善，从而在整个通光孔径范围内，对于反射镜上的一系列测量点，峰值反射率值超过56%。对于非偏振光，该收集器反射镜涂层的相应面积加权2%带内平均反射率超过52%。
The source output power and lifetime, including the collector optics lifetime, are among the key issues for EUV lithography systems. In order to meet the requirements for the EUV collector mirror, both the reflectivity and the long-term thermal stability of its multilayer coating have been enhanced considerably during recent development efforts. Sub-aperture ellipsoidal mirrors of different substrate materials with outer diameters of about 320 mm were coated with laterally graded high-temperature multilayers. The interface-engineered Mo/Si multilayer mirror (MLM) coatings were optimized in terms of high peak reflectivity at 13.5 nm and working temperatures above 400°C. Thin barrier layers were introduced on both interfaces to block thermally induced interdiffusion processes of molybdenum and silicon and to provide long-term optical stability of the coating at elevated temperatures. A normal-incidence reflectance of R ~ 60 % at 13.5 nm was measured on Si wafer samples after heating up to 600°C. No degradation of the optical properties of these multilayer coatings occurred during both long-term heating tests and multiple annealing cycles. On highly polished collector substrates with improved surface roughness a reflectance for s-polarized light exceeding peak values of R = 57 % was obtained. With optimized layer gradient the degree of wavelength matching was improved, as well, resulting in peak reflectivity values above 56 % throughout the clear aperture for a series of measurement points across the mirror. The corresponding area-weighted 2% in-band average reflectance for this collector mirror coating exceeds 52 % for unpolarized light.