基于矢量光束偏振特性的薄膜参数表征  

Characterization of Thin Film Parameters Based on Polarization Properties of Vector Beams

作　　者：李金花 曹兆楼 郑改革 Li Jinhua;Cao Zhaolou;Zheng Gaige(International Joint Laboratory on Photonics and Optoelectronic Detection for Meteorology,School of Physics and Optoelectronic Engineering,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China;Jiangsu Key Laboratory for Optoelectronic Detection of Atmosphere and Ocean,School of Physics and Optoelectronic Engineering,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China;School of Physics and Optoelectronic Engineering,Nanjing University of Information Science&Technology,Nanjing 210044,Jiangsu,China)

机构地区：[1]南京信息工程大学物理与光电工程学院江苏省气象光子学与光电探测国际合作联合实验室,江苏南京210044 [2]南京信息工程大学物理与光电工程学院江苏省大气海洋光电探测重点实验室,江苏南京210044 [3]南京信息工程大学物理与光电工程学院,江苏南京210044

出　　处：《光学学报》2024年第14期112-118,共7页Acta Optica Sinica

基　　金：国家自然科学基金(42375127)。

摘　　要：传统椭偏仪表征薄膜参数时存在光斑尺寸较大、空间分辨率较低且基底透明时易受背面反射光干扰等问题。针对这些问题,提出采用高数值孔径显微物镜聚焦线偏振光的方法,以形成矢量光束照明薄膜。紧聚焦光束由不同角度入射光线组成,受到薄膜反射系数的影响,光束反射时形成结构化图案,且图案细节与薄膜参数密切相关,通过对反射光束进行成像即可反演薄膜参数。基于电磁理论数值模拟了薄膜不同参数对反射光场的影响,并进行了实验验证。结果表明,反射光场对薄膜参数的变化较为敏感,硅表面二氧化硅薄膜厚度的反演误差低于2 nm,重复测量误差低于0.3 nm。该方法得到的光斑尺寸接近衍射极限,显著提高了空间分辨率,在纳米结构表征领域的应用前景广阔。Objective Layered thin film characterization is significant for the fabrication of micro/nano structures. It is necessary to accurately measure refractive indices and thicknesses of films for ensuring the performance of micro/nano structures. As ellipsometry has high efficiency without intrusion, it nowadays serves as a metrology workhorse for critical dimension determination of nanostructures by comparing measured phase retardation and intensity variation between s/p-polarized reflected beams with theoretical prediction. However, traditional ellipsometry employs a quasi-plane wave to illuminate the sample, resulting in low spatial resolution and potential interference of the reflected light at the other surface for transparent substrates. Additionally, the illumination and detecting arms should be mechanically rotated to adjust the illumination angle for angle-resolved measurements, which requires high stability and reliability. Thus, it is desirable to develop a metrology system capable of measuring without mechanical movements. To this end, we propose a polarization imaging system with a tightly focused vector beam as the light source. As rays from different positions of the aperture provide angle-resolved illumination, the reflected spot images contain information on multi-angle s/p-polarized reflection coefficients, which can be further employed to retrieve film parameters. Compared with ellipsometry, the spot size is close to the diffraction limit in the proposed method, which significantly improves the spatial resolution, reduces the focal depth, and helps avoid mechanical rotation.Methods A numerical procedure is developed to simulate the reflection of a vector beam on layered films. The amplitude of rays from different positions of the pupil is traced during the reflection based on coordinate system transformation. The angular spectrum theory is adopted to calculate the propagation of focused beams in the free space. By utilizing the proposed numerical method, datasets relating x/y-polarized reflected sp

关 键 词：偏振 矢量光束 薄膜参数 反射 逆问题 

分 类 号：O436[机械工程—光学工程]