【作者】 邓元龙；

【导师】 姚建铨；

【作者基本信息】 天津大学 ， 物理电子学， 2007， 博士

【摘要】 纳米级厚度薄膜在微电子、材料与化学工程、光学与激光技术等诸多科学领域有着广泛的应用。针对自动光度式椭偏仪的缺点及工业现场的实时、在线测量要求,本文对外差干涉椭圆偏振测量技术进行了系统的理论分析和实验研究。实验系统包括外差光源、稳频电路、外差信号处理、相位差测量和光学系统设计等环节,重点研究了非线性混频误差的产生机理及对外差干涉椭圆偏振测量的影响。实验数据与理论分析基本一致。利用抗干扰能力强的外差干涉法与椭偏测量术相结合,首次系统的完成了纳米薄膜外差干涉椭圆偏振测量理论的应用基础研究。根据具体的纳米薄膜模型,研究了椭偏参数复灵敏度因子的变化规律及误差传递的约束关系,明确给出了膜厚纳米级测量精度与外差信号幅值、相位差检测精度之间的数值关系式。分别采用纵向塞曼激光器和声光调制器作为外差频率源,设计了反射式和透射式两种干涉式椭偏测量系统光学结构,原理分析表明这种分频、共光路的结构设计能有效提高系统抗干扰能力;系统中没有机械旋转部件,在保留椭偏测量优点的同时,可以提高系统稳定性和测量速度。弱磁场中的纵向塞曼激光器输出40KHz的拍频信号,采用光强比较法、热补偿法和模拟PID调节器实现了稳频控制。设计了相位直接比较和高频脉冲填充计数的测相电路,相位差测量分辨力达到0.12°。设计并完成了模拟信号处理及计算机接口电路、椭偏方程反演程序。首次实现了在非恒温、大干扰环境中,纳米级精度的外差干涉椭偏薄膜测量,并分析了入射角测量误差、拍频稳定度、测相电路误差和环境干扰对测量数据的影响。采用琼斯矢量法,首次综合的分析了偏振椭圆化、偏振非正交和偏振器件分光误差同时作用时,非线性混频误差的产生机制及其对外差干涉椭偏测量精度的影响。分析结果表明由此产生的膜厚测量误差可达数纳米量级,非线性混频误差是影响外差干涉椭圆偏振测量实用化的关键因素。椭偏参数|ρ|受误差因素影响较大,应该优先选用Δ求解薄膜参数。光束偏振态(椭圆化和非正交)对测量影响较大,挑选合适的激光源和波片是实现纳米精度测量的前提。定义了误差评价因子,用于预估非线性混频误差幅值的大小和选择合适的椭偏测量方式。非线性混频误差的分析结果对外差干涉式椭偏测量系统的设计有重要的指导意义。更多还原

【Abstract】 The films with thickness of nanometers have wide applications in the fields of microelectronics, materials and chemical engineering, optical and laser technology. For aiming at the disadvantages of spectroscopic ellipsometers and the requirements of in-situ and real time measurement, in this dissertation the heterodyne inteferometric ellipsometry are studied systematically. The experimental system consists of heterodyne light source, frequency stabilization system, heterodyne signal processing, phase-differences measurement and the design of optical system, the analysis of nonlinear frequency mixing error are attached more importance. The experimental results fit well with the theoretical analysis.For the first time, the application of heterodyne interferometric ellipsometry to nanometer films’measurement is studied systematically at the base of fundamental ellipsometry equations and the heterodyne interferometry with high anti-interference performance. For a specific model of nanometer films, the variation rules of the complex sensitivities of ellipsometric parameters are analyzed and calculated theoretically. For reaching nanometer accuracy, the measurement requirements of the amplitudes and phase differences of heterodyne signals are given.By adopting longitudinal Zeeman laser and two acousto-optical modulators respectively, the optical system of reflection and transmission ellipsometers are designed and analyzed by Jones Vector method. It shows the frequency-separation and common-path configuration is helpful to improve the anti-interference performance. Without any rotational mechanical parts, the measurement system is expected to operate at higher speed and stability.Laser frequency stabilization is realized by light intensity comparison, thermal compensated method and analogue PID controller, the longitudinal Zeeman laser located in weak magnetic field outputs a beat signal with 40KHz. The resolution of phase detection reaches to 0.12°by using direct comparison and counting method. The analog signal processing, computer interface and the programs of ellipsometry equation’s inversion are also built up. The films measurement with nanometer accuracy by heterodyne interferometric ellipsometry is realized for the first time under the disturbed environment without constant temperature control. The influence of the errors of incident angle, beat frequency’s stability, phase measuring technique and the environmental disturb on measurement are studied.By using Jones Vector method, the mechanism of nonlinear frequency mixing error and its influence on measurement accuracy are studied synthetically, it is mainly caused by the imperfection of polarizing beam splitters (PBS), the elliptical polarization and non-orthogonality of light beams. As the main obstacle to the practical application of the heterodyne interferometric ellipsometry, it results in an error up to several nanometers of the thickness measurement of thin films. Comparably speaking, the ellipsometric parameterΔshould have the priority for the inversion algorithm because |ρ| is affect greatly by the errors. The laser source and wave plate with high quality are prerequisite to reach nano-accuracy because the elliptical polarization and non-orthogonality have major effect on the measurement results. The definitions of the error evaluation-factors are defined to pre-estimate the error magnitude of ellipsometric parameters. The analysis results are used as foundation for optimum design of the heterodyne interferometric ellipsometer.更多还原