【作者】 干蜀毅；

【导师】 付绍军；

【作者基本信息】 中国科学技术大学 ， 同步辐射及应用， 2008， 博士

【摘要】 真空紫外反射镜在太阳物理、宇宙物理、生命科学、同步辐射等高科技领域应用广泛。近年来,随着国民经济的高速发展,科技能力的快速提升,国内相关行业对真空紫外(VUV)光学元件的需求越来越多。对VUV反射镜制作工艺进行系统、深入的研究显得十分必要。本课题的目的是研究几种常用薄膜材料在50～200nm波长范围内(VUV波段)的反射特性及相关因素对反射率的影响,在此基础上,为制作高反射率真空紫外反射镜及相关光栅涂层提供优化参数。本文主要包括三个方面的内容:1.VUV反射膜反射特性研究基于国内外VUV反射镜研究现状,针对不同的应用波长,分别选定Au、Ir作为50-100nm波段反射镜膜材、Al+MgF2作110-200nm波段反射镜膜材。建立了基底为吸收材料时的单层金属膜和双层吸收膜数学计算模型。以光学工程中常用材料熔融石英、K9玻璃及Si为基底,计算了不同厚度的Au膜、Ir膜和Al+MgF2膜在不同基底上的反射率,并确定了最高VUV反射率时所对应的膜厚。分别以不同的工艺参数和不同的沉积方法(离子束溅射,电子束蒸发),在K9、石英玻璃和Si基片上镀制了不同厚度的薄膜,在科大国家同步辐射实验室“光谱辐射标准和计量线站”上测试了镀制的反射膜在115-140nm波段上的反射率,系统、深入地研究了其反射特性与各种工艺参数间关系。结果表明:1)基片材料对真空紫外反射镜反射率有重要影响。宜以石英或K9玻璃作基底,两者区别不明显,Si明显差。115-140nm波长范围内正入射反射率Au膜达24%,Ir膜近30%,Al+MgF2膜75%;2)膜厚对反射率有重大影响。在采用镀前离子清洗的情况下,石英基片上最佳Au膜厚度约为30nm,Ir膜约12nm;K9基片上稍厚(Au:30nm～40nm,Ir:12～18nm);而对Si片,厚膜好;对Al+MgF2膜,Al膜厚度应在60nm以上,MgF2厚度则需根据入射波长优化;3)镀膜前用能量适当的离子束对基片进行离子清洗,可明显降低基片表面粗糙度,有益于VUV反射率的提高;4)离子束溅射沉积时,溅射离子能量对反射率影响大,存在一最佳值。离子束能量低于此值,反射率明显下降。高于此值,膜反射率几乎不变;5)与电子枪热蒸发相比,离子束溅射得到的反射膜晶粒平均尺寸较小,与玻璃基底的附着力好,镀制过程相对简单,膜厚好控制,稳定性、重复性好;6)为提高Au膜与基底附着力而使用的过渡层越薄越好。过渡层材料对反射率影响不大;7)厚度较薄的膜层对表面具有明显的“均匀化”效应,即粗糙度大的表面覆盖一层薄膜后,粗糙度会得到改善,而光滑表面覆盖一层薄膜后,粗糙度会变差。成膜后的表面粗糙度对反射率影响比基片表面粗糙度要大得多;鉴于这一结果,对基片表面粗糙度提出的要求不必过高,1nm左右即可。8)热处理后膜应力有所释放,但晶粒平均尺寸变大,反射率下降。9)相对于Au膜,Ir膜获得的VUV反射率较高。就膜-基附着力来看,也以Ir为佳;10)镀前溶剂清洗工艺对反射率无明显影响。2.反射率计测试误差分析对反射率测试装置(反射率计)的测试误差进行了详细分析,有针对性地提出了提高测试效率和测试精度的方法,保证了测试结果的可靠性;3.用多重分形谱评价光学表面粗糙度针对实验过程中遇到的光学表面粗糙度评价问题,第一次将多重分形谱(MFS)引入光学表面粗糙度评价体系中,以克服常规评价方法下评价值随取样尺寸、位置发生变化的弊端。计算了熔融石英、K9玻璃及Si片的表面的MFS谱线,表明MFS能够区分不同的光学表面状态,受取样点位置、取样尺寸影响小。本论文的主要创新点体现在:第一次从理论和实验两个方面全面、系统地研究了各种工艺参数对真空紫外反射率的影响,给出了制作高反VUV反射镜的优化工艺参数;对反射率计的测试误差进行了系统、深入的分析;第一次将多重分形谱(MFS)引入光学表面粗糙度评价体系中,获得了一些有价值的结论。更多还原

【Abstract】 Vacuum ultraviolet (VUV) reflector has found various applications in many hi-tech fields including solar physics, cosmic physics, life science, and synchrotron radiation. The rapid enhancement of the economical and technological power of our country has made lots of demand for various VUV components including VUV reflector. So it is quite necessary to have a systematical and intensive study on the fabrication of VUV reflector.The main purpose of this thesis is to study the reflective performance of several commonly used film material in 50～200 nm wavelength region and the influence of various fabrication parameters on the reflectivity. Based on these work, optimum fabrication parameters can be presented and VUV reflector with high reflectance can be made. The thesis contains three parts of work: 1. Research on the performance of VUV reflective filmBased on the achievements acquired by other researchers, Au and lr are selected as reflective film material for the wavelength region from 50 nm to 100 nm, and Al covered with MgF2 for the wavelength region from 110 nm to 200 nm. The theoretical models for a single metal layer and a dual-absorbing-Iayer on absorbing substrate were established. The reflectance of Au, Ir, and Al film covered with MgF’2 of different thickness on fused silica, Bk7 glass, and Si wafer substrate, which are commonly used in optical engineering, was calculated, and optimum thickness was therefore determined.The different metal films of various thickness were deposited on various substrate with different fabrication parameter and deposition method (ion beam sputtering and electron beam evaporation). Their reflectance in the wavelength region from 115 nm to 140 nm was measured continuously by the reflectometer located in the National Synchrotron Radiation Libratory (NSRL) at the University of Science and Technology of China (USTC). The relationship between the reflective performance of the films and various fabricating parameters was investigated systematically and intensively. The results indicate:1) The substrate material has an important impact on the VUV reflectance of the film. Fused silica and Bk7 glass are proved to be suitable substrate materials which shows little difference, while Si wafer is not. In the wavelength region from 115nm to 140 nm, the highest normal incidence reflectance acquired is 24% for Au film, nearly 30% for Ir film, and 75% for Al film covered with MgF2.2) The layer thickness has a significant influence on the VUV reflectance of the film. In the case of pre-ion-cleaning, the optimum layer thickness on fused silica is about 30 nm for Au layer, and 12 nm for Ir layer, while on Bk7 glass substrate, a little bit thicker thickness is needed (Au: 30～40 nm, Ir: 12～18 nm). For Si wafer, the thicker the layer, the better the reflectance. As to Al covered with MgF2, the layer thickness of Al should be no less than 60 nm, while that of MgF2 should be optimized according to the incident wavelength.3) Bombardment of the substrate with ion beam of suitable energy before deposition can significantly enhance the VUV reflectance.4) The sputtering ion energy has a significant influence on the VUV reflectance. There does exist a optimum ion energy. The VUV reflectance will considerably decrease when the sputtering ion beam energy is lower than the optimum, while the higher energy contributes little to the enhancement of the reflectance.5) Compared with electron beam evaporation, the reflective film acquired by ion beam sputtering technique has average smaller grain size, better adhesion to the substrate, simpler and stabler deposition process, and easier control of layer thickness.6) The binding layer used for the enhancement of adhesion between film and the substrate should be as thin as possible. The material used for binding layer impacts the reflectance little.7) A layer of very thin film has a noticeable "averaging" effect on substrate surface, i.e. a rather rough surface could be "smoothened", while a rather smooth surface could be rough after covered with a layer of thin film. The surface roughness of film has much bigger influence on VUV reflectance than that of the substrate. So the surface roughness of 1 nm is reasonable for the substrate when it was grinded, better surface roughness is not necessary.8) The annealing of the film does benefit to the release of the tension, but it also causes the increase of average size of the grain and degradation of the reflectance.9) Compared with Au film, Ir layer can get higher VUV reflectance. As far as the adhesion is concerned, Ir layer performs better as well.10) Different solvent cleaning procedure before deposition has little impact on the VUV reflectance.2. Measuring error analysis of the reflectometerA detailed measuring error analysis is given to the reflectometer. Some effective measures are taken to ensure the accuracy and reliability of the measurement.3. Evaluation of optical surface roughness with multi-fractal spectrum(MFS)For the first time MFS was introduced into the evaluation of optical surfaceroughness in order to get rid of some shortcomings such as the variation of the evaluation with sampling size and position, which were generally encountered by conventional evaluation method including power spectrum density (PSD) and root-mean-square (rms) height. The MFS of the surfaces of fused silica, Bk7 glass, and Si wafer substrate were calculated, and the result indicates that MFS can distinguish different surface topographic condition from one another and can be hardly influenced by the sampling size and position.The main innovations of this paper include: for the first time the influence of various fabricating parameters on the VUV reflectance was studied theoretical and experimental, and optimum parameters for the fabrication of high reflective VUV layer were given; a intensive measuring error analysis is carried out for the reflectometer, and for the first time MFS was introduced into evaluation of optical surface roughness and some explorative conclusion was drawn.更多还原