短波软X射线多层膜性能和制备技术研究
文献类型：学位论文
| 作者 | 冯仕猛 |
| 学位类别 | 博士 |
| 答辩日期 | 2001 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 范正修 |
| 关键词 | 软X射线 多层膜 磁控溅射 散射因子 反射率 光子能量 入射角 |
| 中文摘要 | 软X射线多层膜反射元件在天文学、生物样品的全息术、X射线平板印刷术、和X射线激光以及同步辐射装置上等方面都有非常重要的用途。无论采用什么制备技术，多层膜结构始终存在缺陷，总存在一些降低多层膜反射率的杂质原子。论文用X射线的衍射理论系统分析多层膜中杂质对x射线多层膜反射率的影响，并给出了一个反映杂质含量和多层膜反射率关系的公式。这公式表明：杂质对多层膜反射特性的影响与光入射角度、光的波长、杂质的散射因子和杂质含量有关。当入射角度较小，少量杂质就会导致多层膜反射率急剧降低；而入射角度较大，杂质对多层膜反射特性影响相对来说就比较小。入射角度相同时，相对于氧原子和氩原子，水分子对多层膜反射特性的影响最大。另外，固体杂质的集聚因为有晶界对光的强烈散射而导致多层膜反射率明显降低。厚度随机误差也会严重影响多层膜反射特性。本文根据普通光学理论推导出厚度误差与多层膜反射率的关系，理论上说明了微小厚度随机误差会严重降低短波段软X射线多层膜的反射率。实验证明溅射功率稍微波动下制备的W／Si多层膜测量反射率非常低。就是说，软X射线短波段多层膜的制备，对厚度误差控制有更高的要求。本文还强调多层膜界面相关性能减小基底粗糙度对多层膜反射率的影响；如果多层膜界面结构重复性比较好，基底粗糙度导致多层膜反射率的损失就比较小；相反，在多层膜界面结构完全不相关的情况下，基底粗糙度对多层膜反射率影响就很大。所以本文认为计算影响多层膜反射率的Debye-Waller因子时，应该把粗糙度和相关因子统一考虑。论文在两个表面粗糙度不同的基底上制备短波段多层膜，它们的反射率测量值几乎相等，用代有相关因子的德拜公式就能很好解释本文这种观点的合理性。通过对多层膜中不同缺陷与反射率关系的研究，不难发现，要想通过某种方法单独计算某种缺陷的量值是困难的。论文把所有缺陷的集合定义为广义粗糙度，广义粗糙度的值实际上反映了多层膜的综合质量指标。本论文给出了计算这种综合质量指标的计算公式。利用小角度x射线衍射谱和本文计算公式，获得的广义粗糙度值能有效地反映多层膜的实际质量。对于基底是平面的多层膜，可以用经典公式计算其周期厚度，但对基底是曲面的多层膜，从经典公式获得的结构参数误差比较大。论文对该公式进行了数学上的变换，给出了计算周期厚度的另外一个公式，实验上证明用本文公式计算的周期厚度更接近于多层膜实际周期厚度。论文用不同的溅射功率制备单层Mo膜和Mo／Si多层膜，X射线衍射谱显示过低的溅射功率会导致薄膜质量变坏。用不同溅射功率制备的多层膜测量反射率也证明了这一点。论文通过原子散射因子和能量的关系曲线考察了多种材料在不同光子能量区域的光学性能，并通过计算机模拟计算优化了不同波段的材料配对和多层膜结构参数。用磁控溅射技术制备了一系列适用于不同波段的多层膜并给出了它们的反射率。其中W／Si多层膜在光子能量分别为700eV和1200eV以及入射角80°时获得了11％的反射率，Co／C多层膜在光子能量为260eV和入射角75°时有25％的测量反射率。 |
| 英文摘要 | Soft x-ray multilayer optical components are useful for a number of applications, such as microscope, x-ray astronomy, x-ray biologic holography, x-ray lithography, X-ray laser and instrumentation for synchrotron radiation beam lines. However, structures of multilayers, no matter what deposition technique is used, will not be very perfect. There are a number of possible impurity atoms involved in thin film, which leads to a loss of specular refiectivity. Therefore this paper presents the system investigation of the effect of impurity on the refiectivity of multilayer by the theory of X-ray diffraction. A formula describing the correlation of impurity-contents with the refiectivity of multilayer has been given. According to this expression, the refiectivity reduction by the impurity depends on the incidence angle, radiation wavelength, scattering factor and content of impurity. For example, a few impurities can lead to a large loss of refiectivity at the small incidence angle, and to a small decrease of the refiectivity at the large incidence angle. And at the same incidence angle, H_2Ｏ molecules have the strongest effect on refieetivity among all the gas atoms involved in the multilayer. In addition, the solid atoms involved in the film gather, the boundaries of the split phase with more scattering losses can remarkably reduce the refiectivity of multilayers. Thickness errors can also modify the refiectivity. In this paper, a formula expressing the correlation of thickness random errors with the refiectivity of multilayer is derived fi'om the optical theory. According to the formula, the little thickness random error can leads to a great loss of refiectivity of multilayer for short wavelength of soft x-ray. The measured refiectivity of W/Si multilayers fabricated at a slightly undulating sputtering power is very small, that is, short soft x-ray mirrors require better thickness control to give the highest possible reflectivity. In this paper the effects of roughness correlation are stressed on the refiectivity of multilayer. To our knowledge, the drop in refiectivity is possible small when interface morphology is completely replicated from layer to layer, but the refiectivity reduction is large when the different interfacial roughness is completely uncorrelated. Generally, there is a considerable repetition of the interfacial morphology between layers. In such case, both the degree of interfacial roughness correlation and roughness should be incorporated into calculation by describing the reduction of refiectivity by a Debye-Waller factor. In order to prove the judgment, we have fabricated multilayers on substrates with different surface roughness separately, and measured their refiectivity. And the experimental results well proof the correctness of the method. According to our investigation of effects of various defects on the reflectivity, the influence of all defects can be lumped into a factor and can not be distinguished from each other, in this paper the assemble of all defects in multilayer may be defined as a generalized roughness, whose value reflects the integrative quality of multilayer. The formula valid for calculating the value of generalized roughness is given, which provides the value of generalized roughness effectively reflecting the quality of rnultilayer The classical formula for calculating the structure parameters of multlayers deposited on the substrate with R=∞ is well known and reliable. But it cannot provide the precise periodic thickness of multilayer fabricated on the curved surface. Another expression for calculating the periodic thickness is derived from the classical formula. The experimental results show that the periodic thickmess calculated with our formula is in well agreement with the practical periodic thickness. The Mo single thin films and Mo/Si multialyers are fabricated using magnetron sputtering with different sputtering power. The large angle x-ray diffraction(SAXRD) patterns of Mo single thin films are gotten with CuK_u radiation. The XRD patterns show that the quality of thin film will be very poor when the sputtering power is very low. The same conclusion can be extracted frorn comparison of the refiectivity of Mo/Si multilayers fabricated by different sputtering power. This paper presents an overview of optinmm candidates for the energy range between 100～1300eV using the scattering factor at different photoenergy. The cornputer simulations of the desired pair-materials are also given to optimize the structure parameters. Many multilayers for the desired energy of soft x-ray have been fabricated using the magnetron sputtering. Several multilayers show a considerable measured refiectivity at the different incidence angle and different energy. For example, W/Si multilayers have the measured refiectivity of 11% at the photoenergy of 700eV and 1200 eV separately and the 80° incidence angle. Co/C multilayers also show me a reflectivity of 25% at the photoenergy of 260eV and the 75°incidence angle. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15326]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 冯仕猛. 短波软X射线多层膜性能和制备技术研究[D]. 中国科学院上海光学精密机械研究所. 2001. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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