基于Mueller矩阵椭偏仪的纳米压印模板与光刻胶光栅结构准确测量

在纳米压印工艺中,对模板和压印结构的几何参数进行快速、低成本、非破坏性地准确测量具有非常重要的意义.与传统光谱椭偏仪只能改变波长和入射角2个测量条件并且在每一组测量条件下只能获得振幅比和相位差2个测量参数相比,Mueller矩阵椭偏仪可以改变波长、入射角和方位角3个测量条件,而且在每一组测量条件下都可以获得一个4×4阶Mueller矩阵共16个参数,因此可以获得更为丰富的测量信息.通过选择合适的测量条件配置,充分利用Mueller矩阵中的测量信息,有望实现更为准确的纳米结构测量.基于此,本文利用自主研制的Mueller矩阵椭偏仪对硅基光栅模板和纳米压印光刻胶光栅结构进行了测量.实验结果表明,通过对Mueller矩阵椭偏仪进行测量条件优化配置,并且在光学特性建模时考虑测量过程中出现的退偏效应,可以实现压印工艺中纳米结构线宽、线高、侧壁角以及残胶厚度等几何参数更为准确的测量,同时对于纳米压印光刻胶光栅结构还可以直接得到光斑照射区域内残胶厚度的不均匀性参数.     

入射光照对典型光刻胶纳米结构的光学散射测量影响分析

作为一种快速、低成本和非接触的测量手段,光学散射测量在半导体制造业中的纳米结构三维形貌表征方面获得了广泛关注与运用.光学散射测量是一种基于模型的测量方法,在纳米结构待测参数的逆向提取过程中,为降低参数之间的耦合性,通常需要将结构的光学常数作为固定的已知量,即假设结构的材料光学常数不受光学散射仪入射光照的影响.事实上,这一假设对于半导体制造业中的绝大多数材料是成立的,但某些感光材料的光学常数有可能随着入射光的照射时间增加而发生改变,而由此产生的误差会在一定程度上传递给待测形貌参数的逆向提取值.本文针对聚甲基丙烯酸甲酯光刻胶薄膜培片和光栅结构分别开展了光学散射测量实验与仿真研究,结果表明该光刻胶材料的光学常数随着入射光照时间增加而变化,进而导致光栅结构形貌参数的提取结果较大地偏离于真实值,不容被忽视.这一研究发现将为更进一步提高光刻胶纳米结构三维形貌参数的测量精确度提供理论依据.     

DRC-MME高级参数模型直通标定实验的自由度分析

在椭偏测量中,采用直通式标定方法准确标定出系统模型参数对于样品的精确测量至关重要.由于双旋转补偿器式Mueller矩阵椭偏仪(DRC-MME)高级参数模型复杂,参数数量较多,且部分高级参数之间存在相互级联和耦合,为保证标定结果的准确性,实验中各个参数之间的独立性关系需要被检验.针对这一问题,使用奇异值分解、泡利矩阵和其他数学工具,从理论上对DRC-MME直通标定实验的自由度进行研究分析,明确在数据拟合过程中的"无用"参数,并通过仿真实验验证研究分析结果的正确性.最后搭建实验平台,开展了直通标定实验,得到了符合实际物理意义的高级参数标定结果,并使用标定好的高级参数模型对硅衬底上二氧化硅薄膜厚度进行了测量,测量结果与标称值相差1.9 nm,重复测量精度为5.31 pm.所提对直通标定实验自由度的研究分析方法不仅适用于椭偏仪,也可为其他的多参数优化过程提供一个分析思路.     

激光照射下的低温氧化生成锗的纳米结构及其特性

在高精度椭偏仪（HPE）系统中，采用激光照射硅锗合金衬底助氧化的新方法，在SiO2层中生成锗的双纳米面结构；并在样品生长过程中，用HPE同步测量样品的纳米结构. 用Raman光谱仪测量样品的横断面，发现很强的PL发光谱峰. 用量子受限模型和改进的量子从头计算（UHFR）方法分析了PL光谱的结构. 关键词： 高精度椭偏仪 锗的纳米结构 PL光谱 量子受限     

基于棱镜的椭偏法测量液体复折射率

通过引进等腰棱镜,利用椭偏测量技术实现了液体复折射率的精确测量.基于菲涅尔公式及椭偏测量原理,从理论上分析仪器测量得到的椭偏参数与棱镜-液体界面椭偏参数的关系,并讨论了测量液体折射率及吸收系数的精度.使用消光式椭偏仪,测量了水和印度墨水的复折射率,得到了样品的折射率、吸收系数随浓度变化的实验曲线,实验结果与参考文献基本一致.实验表明:棱镜椭圆偏振技术测量液体折射率及吸收系数的精度分别为0.000 4和0.000 3,适合于快速测量.     

基于双折射晶体的快拍穆勒矩阵成像测偏原理分析

针对传统穆勒矩阵成像测偏仪包含活动部件,需进行多次测量,容易产生测量误差,不能对运动目标或动态场景进行同时、实时测量等问题,提出了一种以改进型萨瓦偏光镜为核心分光器件的快拍Mueller矩阵成像测偏技术(MSP-SMMIP).它不含任何活动部件,能通过单次快拍测量获取目标强度图像和全部16个穆勒矩阵阵元图像.它主要由偏振态产生和偏振态分析两部分组成,偏振干涉条纹通过偏振态产生光路后定位于测试样品上,随后这些条纹通过空间载频将样品的Mueller矩阵分量编码,经偏振态分析光路成像于焦平面上.采用斯托克斯矢量-穆勒矩阵形式阐明了光场偏振态被MSP-SMMIP调制的过程,给出了其像面干涉图表达式,讨论了Mueller矩阵反演和系统定标的方法.基于CCD相机参数分析了系统的光学指标.通过数值模拟实验给出模拟测量结果,通过定性和定量评价测量结果表明该系统的可行性.MSP-SMMIP技术具有稳态、快拍、结构简洁、易定标、可同时实时获取目标强度图像和全部Mueller矩阵阵元图像的显著特点.     

椭圆偏振光谱测量技术及其在薄膜材料研究中的应用

椭圆偏振光谱测量技术通过测量线偏振光经材料表面反射后光的相对振幅与相位改变量计算得到椭偏参数,再通过椭偏参数的拟合获取样品光学性质。由于其具有非接触、高灵敏度、非破坏性等优势,广泛应用于物理、化学、材料科学和微电子等方面,是一种不可或缺的光学测量手段。本文首先简要回顾了该技术的发展历程,接着阐述了传统椭偏仪的基本原理,按照测量原理的不同可将椭偏仪分为消光式和光度式。随后,本文简单介绍了一些常用椭偏仪的基本架构、测量原理和相关应用,并比较了他们的优缺点,重点展示了复旦大学研制的双重傅立叶变换红外椭偏光谱系统。然后按照椭偏参数处理的基本步骤:测量、建模与拟合3个方面,阐述了其过程,详细剖析了参数拟合所使用的各种光学色散模型,同时通过应用实例介绍了各色散模型的应用情况。最后,对未来椭偏技术的发展方向进行了展望。     

椭偏与光度法联用精确测定吸收薄膜的光学常数与厚度

介绍了一种同时利用椭偏仪和分光光度计精确测量薄膜光学常数的方法, 并详细比较了该方法与使用单一椭偏仪拟合结果的可靠性.采用可变入射角光谱型椭偏仪（VASE）表征了250—1700 nm波段辉光放电法沉积的类金刚石薄膜,研究发现当仅用椭偏参数拟合时,由于厚度与折射率、消光系数的强烈相关性,无法得到吸收薄膜光学常数的准确解.如果加入分光光度计测得的透射率同时拟合,得到的结果具有很好的惟一性.该方法无需设定色散模型即可快速拟合出理想的结果,特别适合于确定透明衬底上较薄吸收膜的光学常数. 关键词： 光学常数 光谱型椭偏仪 吸收薄膜 透射率     

光谱型椭偏仪对各向异性液晶层的测量

探讨了利用普通光谱型椭偏仪对各向异性液晶层进行综合性测量的可行性. 并利用法国Jobin Yvon公司的UVISEL SPME(Spectroscopic Phase Modulated Ellipsometer)光谱型椭偏仪测量了光学各向异性液晶层的折射率n_o和n_e及液晶层厚d，进一步利用椭偏仪在透射方式下测量了平行排列液晶层的光延迟特性Δnd，二者取得了很好的一致性，说明利用光谱型椭偏仪可以实现对光学单轴性液晶层及其他材料的测量，测厚精度为纳米量级. 关键词： 光谱型椭偏仪 各向异性 折射率 相位延迟     

基于光谱椭偏仪的纳米光栅无损检测

本文制备了硅基和光刻胶两种材料的纳米光栅,利用光谱椭偏仪对该纳米结构的光栅进行了测量,随后利用建立的拟合模型对其测量数据进行了拟合,结果证明了运用该仪器进行纳米光栅结构无损检测的可行性,在入射角60?,方位角75?的测量条件下,纳米结构关键尺寸、侧壁角等三维形貌参数的测量精度最大可达99.97%,该技术对于无损检测有着一定的推动意义.     

Characterization of grating structures by Mueller polarimetry in presence of strong depolarization due to finite spot size

In this paper, we present an approach based on Mueller polarimetry for dimensional characterization of periodic structures with sample sizes smaller than the illuminating beam spot. The relevant theoretical background based on Mueller matrix formalism is presented. The sample, a photoresist grating box surrounded by silicon substrate, was measured in conical configuration by means of a spectroscopic Mueller polarimeter whose beam was illuminating both the grating and the substrate. By translating the boundary between these two regions through the beam we could follow the depolarization effect related to the incoherent superposition of the light reflected by the grating and the substrate. The grating’s optical response was modeled by rigorous coupled-wave analysis. The optimized geometrical parameters of the grating (the line width, the grating depth, and the side-wall angle) show very good consistency for all sample positions with 15% or more of the spot area covered by the grating. Another source of depolarization, the finite spectral resolution of the polarimeter was also taken into account in the analysis, leading to a good quantitative agreement with the sharp “depolarization lines” observed in the measured Mueller spectra.     

Multichannel Mueller matrix ellipsometer for real-time spectroscopy of anisotropic surfaces and films

A multichannel ellipsometer in the dual-rotating-compensator configuration has been developed for potential applications in real-time Mueller matrix spectroscopy of anisotropic surfaces and films. This instrument provides spectra (1.7-5.3 eV) in all 16 elements of the unnormalized Mueller matrix M of a film-substrate system with a minimum overall data acquisition time of t(a) = 0.25 s. We have applied this instrument first for high-precision determination of spectra in M with t(a) = 2.5 s for a microscopically sculptured film.     

Differentiating characteristic microstructural features of cancerous tissues using Mueller matrix microscope

Polarized light imaging can provide rich microstructural information of samples, and has been applied to the detections of various abnormal tissues. In this paper, we report a polarized light microscope based on Mueller matrix imaging by adding the polarization state generator and analyzer (PSG and PSA) to a commercial transmission optical microscope. The maximum errors for the absolute values of Mueller matrix elements are reduced to 0.01 after calibration. This Mueller matrix microscope has been used to examine human cervical and liver cancerous tissues with fibrosis. Images of the transformed Mueller matrix parameters provide quantitative assessment on the characteristic features of the pathological tissues. Contrast mechanism of the experimental results are backed up by Monte Carlo simulations based on the sphere–cylinder birefringence model, which reveal the relationship between the pathological features in the cancerous tissues at the cellular level and the polarization parameters. Both the experimental and simulated data indicate that the microscopic transformed Mueller matrix parameters can distinguish the breaking down of birefringent normal tissues for cervical cancer, or the formation of birefringent surrounding structures accompanying the inflammatory reaction for liver cancer. With its simple structure, fast measurement and high precision, polarized light microscope based on Mueller matrix shows a good diagnosis application prospect.     

Extraordinary Transmission through Metallic Grating with Subwavelength Slits for S-Polarization Illumination

Based on the rigorous coupled-wave analysis algorithm, we have systematically analysed the effect of the geometrical parameters of a dielectric film coated metallic grating with subwavelength slits on extraordinary optical transmission for s-polarization illumination. Results show that the dielectric film which sustains a waveguide electromagnetic mode on the top of the metallic lamellar grating can strongly enhance the transmittance, the positions of the transmission peaks are mainly determined by the period of the metallic grating, the thickness and refractive index of the dielectric film. This structure shows potential applications in excellent polarizers or polarization-isotropic devices at infrared spectral range by appropriately choosing the geometrical parameters.     

Snapshot imaging Mueller matrix polarimeter using polarization gratings

A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation. Spatial polarization fringes are localized onto a sample by incorporating polarization gratings (PGs) into a polarization generator module. These fringes modulate the Mueller matrix (MM) components of the sample, which are subsequently isolated with PGs in an analyzer module. The MM components are amplitude modulated onto spatial carrier frequencies which, due to the PGs, maintain high visibility in spectrally broadband illumination. An interference model of the SIMMP is provided, followed by methods of reconstruction and calibration. Lastly, a numerical simulation is used to demonstrate the system's performance in the presence of noise.     

Polarimetric target detection in the presence of spatially fluctuating Mueller matrices

In polarimetric imaging systems, the main source of perturbations may not be detection noise but fluctuations of the Mueller matrices in the scene. In this case, we propose a method for determining the illumination and analysis polarization states that allow reaching the highest target detection performance. We show with simulations and real-world images that, in practical applications, the statistics of Mueller matrix fluctuations have to be taken into account to optimize polarimetric imagery.     

三代微光像增强器信噪比测量技术研究

微光像增强器是微光成像技术中的核心部件,微光像增强器的信噪比是像增强器的重要参数之一,它可以定量表征像增强器在探测弱辐射图像时的性能,可综合反映空间因素和时间因素对探测图像特性的影响。介绍了微光像增强器信噪比的测量原理和装置,测量装置采用精确的微孔光阑、可变光阑及共轭对称透镜系统,实现直径为0.2 mm的特定光斑投射在像增强器光阴极面上。采用光子计数技术,通过研究小探测面（探测直径小于4 mm）微弱光照度标定方法,解决了针孔微弱光照度的准确标定与直径为0.2 mm信噪比光源照度准确测量。     

Polarization modulation imaging ellipsometry for thin film thickness measurement

A polarization modulation (PM) imaging ellipsometer is proposed and setup in order to measure precisely the thickness of thin film. Five images are collected sequentially by CCD camera with respect to five pre-determined azimuth angles of a quarter wave plate (QWP) during measurement. Then two-dimensional (2-D) distributions of the ellipsometric parameters ψ and Δ over the full dynamic range are obtained. Conceptually, PM imaging ellipsometer integrates the features of phase shift interferometry with conventional photometric ellipsometry by rotating the QWP sequentially to produce polarization modulation that is able to measure the thickness of a thin film in two dimensions precisely and quickly. The basic principle of PM imaging ellipsometer is derived wherein features such as common path configuration, full dynamic range of measurement, and insensitive to non-uniform response of the CCD are analyzed. The experimental results verify the ability and performance of PM imaging ellipsometer on 2-D thin film thickness, while the errors regarding the ellipsometric parameters measurements are discussed.