电子薄膜的电子探针能谱分析技术研究

【作者】 李世岚；

【导师】 包生祥；

【作者基本信息】 电子科技大学 ， 材料学， 2008， 硕士

【摘要】 对于电子薄膜材料研究,薄膜的微观结构、成分和厚度是决定薄膜性能的一个关键因素。如何表征薄膜的微观结构、成分和厚度也一直是薄膜研究领域的一个重要课题,尤其是应用无损表征方法。扫描电子显微镜配备X射线能谱仪分析技术（电子探针能谱）能够观察微观形貌和分析薄膜的微区成分的同时,根据电子束的穿透深度可测量薄膜的厚度。其它任何薄膜分析技术都无法同时具备以上三个功能。采用电子探针能谱分析技术时,由于X射线激发深度较大,当薄膜厚度较小时,会同时出现薄膜层和基片的谱线,严重影响薄膜成分的分析结果。为了排除基片谱线对薄膜成分分析的干扰,本论文针对电子薄膜与集成器件国家重点实验室研制的微米及纳米薄膜材料成分与厚度表征的需要,开展了如下研究:1.在常规电子探针能谱分析系统的基础上,建立的掠出射角电子探针能谱分析方法,并对该分析方法进行了系统验证。通过对金属铜膜和Cd掺杂氧化锌半导体薄膜的掠出射电子探针能谱分析与常规出射电子探针定性分析对比、不同出射角条件下不同线系特征X射线的强度研究、样品倾斜对电子探针能谱定量分析精度影响等方面进行了研究,证明了该方法能够很好的解决许多电子探针常规出射分析薄膜样品时存在的困难,如电子有效作用范围深度减小,具有很好的表面灵敏性,衬底产生的荧光效应能降至最低,薄膜定量分析精确度提高。2.研究了在常规电子探针能谱系统中如何提高薄膜成分分析准确度的方法。从薄膜成分的电子探针能谱分析得出:同一元素的不同线系特征谱线,是影响分析结果最重要的因素。对于具有荧光效应的衬底薄膜:所选元素的特征谱线应具有衬底的荧光效应;对于不具有荧光效应的衬底薄膜:当过压比足够时,选择峰背比最大的特征谱线,在特征谱线选择正确的前提下,工作电压越大,分析结果越准确。3.研究发展了电子探针能谱薄膜厚度的测量技术。根据电子束的穿透深度计算薄膜的厚度。对于单一组分薄膜:可以直接通过外推衬底与薄膜特征峰强度之比(Ⅰ_衬底/Ⅰ_薄膜)至“0”,对应的加速电压即为薄膜的归一化电压E_d（开始不能检测到衬底的特征X射线）;而对于多组分薄膜样品,若衬底和薄膜中都含有相同元素时,借助与薄膜组份含量相同的块材标样,分别得出薄膜样品中衬底与薄膜特征峰强度之比与加速电压之间的关系,以及块材标样样品相应元素的特征峰强度之比与加速电压之间的关系。当薄膜样品中衬底与薄膜特征峰强度比的变化率与块材标样样品相应元素的特征峰强度比的变化率一至时,对应的加速电压即为多组份薄膜的归一化电压E_d。4.对薄膜样品中轻元素的电子探针能谱定量分析研究。通过应用轻元素标样对低能量端的峰位进行低能量端峰位校准,使低能量端的峰与模拟线很好的吻合;逐渐降低工作电压直至电子穿透深度刚好等于薄膜厚度时,能最大程度减少基片和表面吸附的影响,并结合EDAX能谱分析软件的SEC因子,可以获得令人满意的分析结果。更多还原

【Abstract】 Microstructure, component and thickness are key factors to determine the performances in research of thin films. The methods to characterize microstructure, component and thickness of thin fihns are all through important issues in thin films field, especially the non-destructive characterization. The observation of microstructure, analysis of components in tiny regions and measurement of thickness according to penetration depth can be realized with Scanning Electron Microscope and X-ray Energy Dispersive Spectrometer (EPMA), while any other thin film-analyzing approaches don’t possess the above three function simultaneously.Using EPMA analysis technique, when thickness of thin films is less, the spectrum line of thin film and substrate appears at the same time, which affects the element analysis results of thin films severely. To eliminate the interference from substrate spectrum, this paper discuss the following research means, aiming at analyzing and characterizing the micro- and nano-materials of thin films in the State Key Laboratory of Electronic Thin Films and Integrated Devices.1. Based on the general EPMA system, grazing-exit EPMA (GE-EMPA) analysissystem is set up and evaluated systematically. Through qualitative analysis between the GE-EMPA and general EMPA of Cu metal thin film and ZnO semiconductor thin film adulterated with Cd, different characteristic X-ray intensity with different exit angle, the effect of incline to the quantitative analysis of electron probe spectrum, and some other studies, this method is proved to solve many problems of analyzing general electron probe exit of thin films, such as depth decrease of electron effect range, good surface sensitivity, fluorescence effect from the substrate dropping to the bottom, increased precision of quantitative analysis for thin films, etc.2. The methods for improving analysis precision of thin fihns are demonstrated with general EMPA analysis technique. From the X-ray spectrum analysis of thin films, it’s found that-different characteristic X-ray line of one element is a factor that impacts the analysis result most. For thin films and substrate with fluorescence effect, if any element is affected by fluorescence from substrate, characteristic X-ray line of the chose elements should have fluorescence effect from the substrate. For thin films and substrate without fluorescence effect-with enough overvoltage ratio, the biggest peak to background ratio (P/B) should be chose; when the characteristic X-ray line is chose exactly, the bigger work voltage is, the more precise analysis result.3. Thickness measurement of thin films with EMPA is investigated. According to the penetration depth of electron beam, thickness of thin films is calculated. For the thin film with single element, with extrapolating the characteristic X-ray peak ratio of substrate to thin film to "0", the corresponding accelerating voltage is the normalization voltage Ed (the characteristic X-ray of substrate can’t be tested at the beginning). For thin films with many elements, if the thin film and substrate have same elements, the relationship between accelerating voltage and element intensity ratio of thin film to substrate, as well as the relationship between accelerating voltage and standard bulk pattern can be got. The change speed of characteristic X-ray peak ratio of substrate to thin film and standard bulk are identical, the corresponding accelerating voltage is the normalization voltage Ed.4. Quantitative analysis of light elements of thin films is implemented with EMPA. Through adjusting the position of low energy peak marked with light element, low energy peak and simulation line inosculate primely. With decreasing work voltage gradually until electron penetration depth and thickness of thin films are identical, the effect of substrate and surface absorption can be reduced furthest, combining with SEC factor in EDAX spectrum analysis software, satisfactory analysis consequences can be obtained.更多还原