【作者】 吕鹏；

【导师】 关庆丰；

【作者基本信息】 江苏大学 ， 材料学， 2014， 博士

【摘要】 本文对空间EUV望远镜中光学器件及半导体材料进行了荷电粒子束辐照效应研究,利用光学显微镜(OM),扫描电子显微镜(SEM),原子力显微镜(AFM),透射电子显微镜(TEM),极紫外反射率计(EXRR)和光致发光光谱仪(PL)等多种表征及测试手段重点考察了辐照效应对材料微观结构与物理性能的影响。在不同本底真空度下(6×105Torr,3×10-5Torr, and3×10-6Torr)制备“嫦娥三号”卫星着陆器所携带的EUV相机中Mo/Si多层膜反射镜,并对多层膜的微观结构和物理性能进行检测和分析。小角XRD结果显示,本底真空度越高,制备出的多层膜周期性越好；EXRR测量结果显示：多层膜的反射率随着本底真空度的升高,从1.93%升高到16.63%。这主要是因为镀膜机的本底真空度不够高会引入杂质气体,02、N2等杂质气体会进入到膜层内部,TEM照片显示样品出现断开、弯曲等形貌,同时会导致Mo层和Si层相互扩散严重,增加了膜层界面粗糙度,从而导致反射率降低。Mo/Si多层膜高反射率的高低主要取决于Mo在(110)晶面上择优取向以及较低的界面粗糙度。过渡层是由于Mo层和Si层相互扩散引起的,Mo-on-Si层总是比Si-on-Mo层厚。在空间环境模拟装置中对Mo/Si多层膜反射镜进行能量为100keV,剂量为6×1011/cm2和6×1013/cm2的质子辐照实验；利用蒙特-卡洛随机统计法模拟100keV质子及其辐照诱发的缺陷在多层膜内的浓度分布；系统地分析了辐照诱发的各种微观结构缺陷的类型、尺寸、密度、分布等特征及演化规律；分析微观缺陷对Mo/Si多层膜界面的元素扩散行为以及界面过渡层结构的影响规律,总结和建立微观结构与材料物理性能之间的关系。模拟辐照结果显示,质子辐照的过程中的能量损失贯穿整个样品,但是主要集中在Mo/Si多层膜的末段,入射质子在轨迹末端将其绝大部分能量传递给靶材原子(Mo原子和Si原子),造成大量离位原子和空位,产生晶格缺陷,在轨迹末端附近产生最大损伤,而Mo层中的缺陷明显多于Si层；辐照后EXRR测试结果表明：质子辐照导致Mo/Si多层膜反射镜光学性能退化,反射率降低,中心波长红移；质子辐照对Mo/Si多层膜微观结构的影响是原子级的,通过辐照加剧了原子间的扩散导致纳米厚度的膜层分布不均匀,在过渡层中形成了MoSi2(101)和Mo5S13(310)的织构,使得本身就存在的过渡层微结构发生巨大变化,最终导致光学性能的严重下降。采用强流脉冲电子束(HCPEB)装置辐照单晶Si和单晶Ge。HCPEB辐照单晶Si后表面形成大量弥散的火山坑状的熔坑形貌,熔坑的数量密度随辐照次数的增加而减小；OM观察结果显示HCPEB轰击处理还能在单晶硅表面诱发强烈的塑性变形,产生幅值极大及高应变速率的准静态热应力,形成整齐排布的微裂纹,其中[100]取向的形成矩形网络,[111]取向的形成正三角形网络；TEM显示HCPEB辐照在Si表面诱发了丰富的位错组态,包括螺型位错,位错偶极子、位错缠结,和位错网络,这些都位错的分解和拓展有关。除了各种位错之外,还观察到层错、弗兰克位错圈、偏位错圈和SFT结构,这些缺陷不仅包括过饱和空位和由空位凝聚而成的各种空位型结构缺陷,也包括丰富的位错、堆垛层错等线、面晶体缺陷；而过饱和空位(或许包括空位簇缺陷)在HCPEB辐照造成的温度梯度作用下会沿着位错、堆垛层错等择优地向表面快速迁移,在Si表面局部区域形成密集的多孔结构,而孔的密度和尺寸会随着辐照次数的增加而增大；TEM观察结果显示,HCPEB辐照还在Si表面产生改性效果,由于脉冲电子在Si表面的快速加热和冷却过程,使得Si晶核来不及长大,形成了Si纳米晶,PL光谱显示辐照后Si样品具有还410nm(3.01eV)左右的蓝光发射现象,其光致发光机理可以由镶嵌在轻微氧化或氮化的非晶结构中的Si纳米晶的量子限制效应来解释；AFM观察显示,HCPEB辐照在Si表面形成了网格型和六边形白组装纳米阵列,与TEM中的位错网络保持非常一致的几何形状,辐照诱发的位错等缺陷结构对沉积过程中的Si颗粒(原子)更具吸附力,即位错等缺陷结构为自组装纳米网格结构的形成提供了驱动力。HCPEB辐照单晶Ge在表面诱发了大量熔坑,局部裂纹,其形貌特征、演化规律与单晶Si的实验结果大致相同；TEM观察结果显示,Ge中的微观缺陷以空位簇缺陷以及位错圈为主,Ge纳米晶的尺寸在4nm左右,比Si纳米晶的尺寸稍大,而且尺寸分布较均匀,其原因是Ge的熔点比Si的熔点低,相同辐照参数下Ge纳米晶有更长的生长时间：PL结果显示辐照后单晶Ge样品仍然具有蓝光发射特性,发光机理为镶嵌在轻微氧化或氮化的非晶结构中的Ge纳米晶的量子限制效应。HCPEB辐照在Ge表面也形成了自组装纳米结构,截面TEM显示量子点下方存在250nm深的缺陷通道,证实了Si表面的自组装纳米阵列形成机理,因此本文中HCPEB辐照诱发自组装纳米结构机制为：辐照时表面被迅速加热,熔化、蒸发、气化并形成等离子体,而Si, Ge是半导体材料,导电能力弱,电子辐照后表面滞留了大量的负电荷。同时,电子辐照在材料中同时引入点缺陷、位错、空位簇缺陷等具有电荷性的大量缺陷,使得表面电荷分布不均匀,而缺陷处成为负电荷的富集区域,在库仑力的作用下,表面等离子体中带正电荷的Si/Ge离子被吸引到样品表面负电荷富集位置,即缺陷处。而Si2+/Ge2+含有大量的Si/Ge原子和原子团簇,导致Si/Ge原子在表面缺陷附近沉积,在经历四个生长阶段后,最终形成了自组装纳米结构。HCPEB辐照效应说明其具备制备自组装纳米结构和半导体发光器件的潜质。更多还原

【Abstract】 The irradiation effect of optical device in EUV imager and semiconducting materials which irradiated by charge particle beams have been investigated in this study. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Atomic force microscopy (AFM), scanning electron microscope (SEM), EUV/soft X-ray reflectometer (EXRR) and photoluminescence (PL). The relationship between microstructrue and physical properties were investigated in this paper.Mo/Si multilayers mirror for Extreme-ultraviolet imager in Chang’e3lander are fabricated by using magnetron sputtering method at different background pressures:6×10-5Torr,3×10-5Torr, and3×10-6Torr. The microstructure and optical performance of Mo/Si multilayers mirror have been investigated. XRD indicated that multilayers fabricated at high background pressure possessed better periodic structure and thinner Mo-on-Si interlayers. The reflectivity of the Mo/Si multilayers increased from1.93%to16.63%, and the center wavelength revealed a blue shift with the decrease of background pressure. Impurity gas (O2, N2) could seemingly influence the growth and nucleation behavior of Mo/Si multilayers. Low crystallization degree in (110) preferred the orientation of Mo layers and serious interdiffusion in the Mo/Si multilayers fabricated at low background pressure were observed by TEM. In addition, the thicknesses of Mo-on-Si are always thicker than Si-on-Mo interlayers. It is suggested that the influence of background pressures on the microstructure has a critical role in determining the optical properties of Mo/Si multilayers.The microstructure and optical properties of Mo/Si multilayers mirror before and after100keV proton irradiation have been investigated. The concentration distributions of the protons and defects in the multilayer after irradiation of protons with energy of100keV were simulated by the Monte-Carlo method. Type, size, density, distribution and evolution of defect which induced by proton irradiation were systematically investigate. The relationship between microstructure and properties of Mo/Si multilayers have been built. Results of simulated irradiation experiment show that the energy loss in the process of radiation running through the whole sample, but mainly left in the substrate of Mo/Si multilayers. Most energy of incident protons transfer to the target atom (Mo and Si atoms), which caused a large number of displaced atom and vacancies.The defects in the Mo layer significantly more than the Si layer. The results of EXRR show that, after proton irradiation, the reflectivity of the Mo/Si multilayer decreased and the center wavelength shift red, compared with those before proton irradiation. HRTEM observations revealed that the presence of MoSi2, MosSi and MosSi3in Mo-on-Si interlayers before irradiation. However, the preferred orientation such as MoSi12with (101) texture and Mo5Si3with (310) texture were formed in Mo-on-Si interlayers after proton irradiation, which lead to the increase of the interlayers thickness. It is suggested that the changes of microstructures in Mo/Si multilayers under proton irradiation could cause the optical performance degradation.Single crystal silicon and single crystal germanium were irradiated by high current pulsed electron beam (HCPEB) in this paper. A large number of craters and microcrack formed on Si surface after irradiation. The density of crater decreased with the increase of pulse times. OM observation reveals that HCPEB treatment induce intense plastic deformation which generate the maximum amplitude and high strain rate quasi-static thermal stress on the surface Si wafer, formed orderly arrangement microcracks. The microcracks in Si(100) oriented are rectangular network, in Si(111) are equilateral triangle network. TEM observations show that HCPEB irradiation induced abundant dislocation configuration which include screw dislocations, dislocation dipole, tangled dislocation, and dislocation network. All of these are connected with decomposition and extension of dislocation. In addition to all kinds of dislocations, we observed stacking faults, Frank dislocation loops, partial dislocation loops and SFT. These defect are not only include supersaturated vacancies and vacancy type defects by vacancy agglomerates, but also include abundant dislocations (line defects), stacking faults (surface defects). Under the effect of the temperature gradient caused by HCPEB irradiation, supersaturated vacancies (perhaps including the vacancy clusters) preferentially transfer to surface, then formed porous structure on the part area of Si surface. Si nanocrystallites (Si-ncs) formed during HCPEB irradiation. The reason is Si nucleus formed quickly with low growth velocity, which leads to the formed Si crystal nucleus on the top layer of Si wafer are too late to grow up. PL measurements show that single crystal Si wafer exhibit blue photoluminescence emission at room temperature after HCPEB irradiation. The luminescence mechanism is quantum confinement effect of Si-ncs embedded in amorphous silicon oxide or silicon nitride matrix. AFM observation results show the formation of grid type and hexagonal Si self-assembled nano-arrays after HCPEB irradiation, which consist with the geometry of dislocation network in TEM. Defect structures such as dislocations are more adsorption capacity for deposition process of Si particles (atomic). In the other words, defect structure provide driving force for the formation of self-assembled nanostructureA large number of craters and microcrack formed on Ge surface after HCPEB irradiation. Its morphology characteristics and evolution are in accord with the results of Si irradiated by HCPEB. TEM observation results show that the main defects in Ge are vacancy cluster defects and dislocation loop. The size of the uniform Ge-ncs is about4nm, more than the size of Si-ncs. The reason is that the melting point of Ge is lower than Si, under the same irradiation parameters, Ge-ncs have longer time to grow. PL measurements show that single crystal Ge wafer exhibit blue photoluminescence emission at room temperature after HCPEB irradiation. The luminescence mechanism is quantum confinement effect of Ge-ncs embedded in amorphous germanium oxide or germanium nitride matrix. Ge self-assembly nanostructures were prepared by HCPEB irradiation. Crosss-section TEM observe reveals the existence of defects channel with250nm deep below the quantum dot. It is confirmed that the formation reason of self-assembly nanoarray on the Si surface after HCPEB irradaition. Therefore, formation mechanism of self-assembly nanostructures induced by HCPEB irradiation could be defined. The irradiated surface was rapid heating, then melting, evaporating, gasifying and formed plasma finally. The conductive ability of Si and Ge are weak, and a large number of negative charges left on the surface after HCPEB irradiation. At the same time, the irradiation induced many charged defects, such as point defect, vacancy cluster defects and dislocation loop. These defects become the negative charge accumulation area which caused the charge distribution nonuniform on the surface. Then the positively charged Si/Ge ions in plasma were absorbed to the negative charge accumulation area under the action of coulomb attraction. Si/Ge ions contain a large number of Si/Ge atoms and atom clusters. The absorbed atoms formed self-assembled nanostructures after nucleating, island, merging and connecting. HCPEB irradiation effect shows that such a direct and fast treatment can be used as a potential surface modification method for fabricating self-assembled nanostructures semiconductor light-emitting devices.更多还原