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1、华中科技大学 博士学位论文 微纳深沟槽结构基于模型的红外反射谱测量方法研究 姓名：张传维 申请学位级别：博士 专业：机械制造及其自动化 指导教师：史铁林;刘世元 20090901 华 中 科 技 大 学 博 士 学 位 论 文华 中 科 技 大 学 博 士 学 位 论 文 I 摘摘 要要 在微电子和微机电系统设计与制造工艺中，目前普遍采用了高深宽比的深沟槽 结构。随着沟槽尺寸不断缩小且沟槽剖面形貌更为复杂，监测沟槽深度相关的几何 特征参数对于保证工艺控制已变得越来越迫切。目前普遍采用的终点控制法，假定 刻蚀速率等于刻蚀深度除以刻蚀时间。由于刻蚀速率与多种因素有关而在刻蚀过程 中很难保持定值，因
2、此误差较大。为了实现有效的工艺控制，在制造过程中对深沟 槽结构的尺寸进行在线、非破坏性的精确检测具有非常重要的意义。为此，本学位 论文以此为研究背景，系统研究了微纳深沟槽结构基于模型的反射光谱测量理论与 方法，并成功研制开发一套基于模型的红外反射谱测量原型系统。 建立了高深宽比微纳深沟槽结构的等效光学模型，针对一维周期性结构和二维 周期性结构分别提出了一种基于修正等效介质理论的光学反射率计算新方法。通过 对各种典型微纳深沟槽结构反射特性进行仿真分析，探讨了沟槽结构反射光谱特性 与其对应几何特征参数之间的联系。 研究了基于测量光谱反演分析的沟槽结构参数快速提取技术，基于已建立的深 沟槽结构光学特
3、性模型，分别提出了基于自适应模拟退火结合 LM 算法以及人工神 经网络结合 LM 算法的参数提取快速算法，并对以上两种参数提取算法进行仿真分 析，验证该方法在沟槽结构参数提取中的快速性以及提取结构参数的准确性。 研制了一套基于模型的红外反射谱测量原型系统，研究了高灵敏度红外探测光 路设计、硅片样件背部杂散光干扰消除、光谱测量高速数据采集、信号分析及沟槽 参数自动提取软件包开发等关键技术。利用该测量原型系统对多层光学薄膜结构、 典型深沟槽结构进行了实验研究，验证了所提测量理论与方法的有效性和适用性。 本文所研究的基于模型的红外反射谱测量法为深沟槽结构刻蚀在线测量提供了 一种非接触、非破坏、快速、
4、低成本和高精度的新途径，在微机电系统及集成电路 制造过程中的在线监测与工艺控制方面具有广阔的应用前景。特别是在 DRAM 深 华 中 科 技 大 学 博 士 学 位 论 文华 中 科 技 大 学 博 士 学 位 论 文 II 沟槽缺陷原位检测、高深宽比微纳结构刻蚀实时监控、全场硅片 CD 均匀性快速评 估等方面将获得广泛的应用。 关键词关键词：高深宽比 微纳深沟槽结构 红外反射谱 等效介质近似 光谱反演 背光消 除 华 中 科 技 大 学 博 士 学 位 论 文华 中 科 技 大 学 博 士 学 位 论 文 III Abstract Deep trench structures with hi
5、gh-aspect ratio have been widely used in the design and manufacture of microelectronic and microelectromechanical system (MEMS) devices. As devices with deep trench structures have been packed more tightly, the critical dimension (CD) and depth dependent features must now be monitored to ensure proc
6、ess control. The endpoint method is commonly used in the control of etching depth which is assumed to be dependent on etching time multiplied by etching rate, however, the etching depth error using this method is usally very large due to the fact that the etching rate relies on a variety of factors
7、and is difficult to be kept as constant. Therefore, it is important to perform the on line monitoring of etching process of the micro/nano deep trench structures accurately and nondestructively so as to ensure the effective process control. On the basis of such a research background, this dissertati
8、on intends to study systematically on the theory and method of the model-based infrared reflectometry (MBIR) for the micro/nano deep trench structures, and to develop successfully a prototype system of the MBIR metrology. At first, the effective optical model of the micro/nano deep trench structures
9、 with high-aspect ratio has been established. A modeling method named corrected effective medium approximation (CEMA) has been proposed to calculate the reflectivity of the one- dimensional (1-D) and two-dimensional (2-D) deep trench structures, and has been demonstrated to be not only fast in calcu
10、lation but also accurate enough in comparison with the rigorous coupled wave analysis (RCWA) method for both 1-D and 2-D trench structures, hence is especially suitable for the MBIR metrology. Based on such a novel modeling method, extensive simulations have been carried out on typical types of micr
11、o/nano deep trench structures, and thus discuss the relationship between the the reflectance spectrum and the geometric parameters of the trench structures. Then, the extraction of the geometric parameters of trench structures in the MBIR metrology has been investigated as a typical spectral inverse
12、 problem. With the help of the above proposed modeling method, two approaches to fast parameter extracting have been put forward, namely adaptive simulated annealing and Levenberg-Marquardt combined method (ASA-LM) and artificial neural neural network and Levenberg-Marquardt combined method (ANN-LM)
13、. Simulations performed on a 1-D deep trench structure has verified that both of the proposed ASA-LM and ANN-LM methods are accuarate and fast in computation for the parameter extraction. 华 中 科 技 大 学 博 士 学 位 论 文华 中 科 技 大 学 博 士 学 位 论 文 IV Finally, a prototype system of the MBIR metrology for the meas
14、uring of micro/nano deep trench structures is described in detail. Several key technologies involved in developing the system has been investigated, including design of the infrared detecting optical path with high sensitivity, suppression of the noisy reflection from the wafer backside, high-speed
15、signal acquision and processing for the spectral measument, software programming for the signal analysis and automatic parameter extraction, etc. The prototype system has been applied to some multilayer thin films structures and a typical deep trench structure with experimental resutls demonstrated
16、that the trench geometric parameters can be extracted with a nanometer scale accuracy. The proposed MBIR technique is hopeful to provide a non-contact, non-destructive, time effective, low cost and high resolution tool for the measurement of deep trench structures. It is expected that this technique will have potential applications in the on-line monitoring and process control for microelectronics and MEMS manufacturing, and it will be widely used in the trench etching fault diagnosis, in-line
