极紫外宽带多层膜反射镜离散化膜系的设计与制备

极紫外(EUV)宽带多层膜的光谱性能对膜厚控制精度要求较高,仅由时间控制膜厚的镀膜系统难以满足其精度控制要求。本文提出了基于进化算法的宽带EUV多层膜离散化膜系设计方法,与传统膜系设计相比,离散化膜系所制备多层膜具有更为优良的EUV反射光谱性能。为验证离散化膜系设计在宽带EUV多层膜研制中的优越性,采用磁控溅射方法对具有离散化膜系的宽带多层膜反射镜进行了制备和测试。测试结果表明:研制的宽角度多层膜反射镜可实现入射角带宽为0°～17°,高于41%的反射率;研制的堆栈宽角度多层膜反射镜可实现入射角带宽为0°～18.5°,高于35%的反射率;研制的宽光谱多层膜反射镜可实现波长带宽为12.9～14.9 nm,高于21%的反射率。

Design and fabrication of EUV broadband multilayer mirrors with discrete thicknesses

Efficient broadband reflective Extreme Ultraviolet (EUV) multilayers require superior control and precision of layer thickness. A solely time-controlled deposition system can not meet the requirements of high accuracy. In this paper, we present a scheme for the design of broadband multilayers with discrete thicknesses based on an evolutionary algorithm. This method greatly improves the reflectivity curve compared to that of conventional multilayer mirrors without discrete thicknesses. To verify the superiority of the design, the broadband multilayers were deposited using a magnetron sputtering system. The EUV measurements reveal that the deposited aperiodic broad angular multilayers exhibits reflectivity values greater than 41% over an angle of incidence range of 0-17° for a fixed wavelength of 13.5 nm, the broad angular multilayers in four different stacks exhibits reflectivity values greater than 35% with a wide angular bandpass over an angle of incidence range of 0-18.5° for a fixed wavelength of 13.5 nm, and the broadband multilayer mirrors exhibits reflectivity values greater than 21% for wavelengths ranging between 12.9-14.9 nm for a fixed angle of incidence of 3°. This study demonstrates a great potential for the application of discrete design in the fabrication of EUV broadband multilayers with high accuracy.