Generation of perfect circular polarizations and thesr use for development of a precise alignment method for spectroscopic ellipsometers

该项目旨在通过开发一种校准方法，使旋转分析仪椭偏仪（RE）的总体精度达到0.1%，该方法通过生产和使用完美的圆偏振来实现0.02%的精度。椭偏测量中的误差来源归因于仪器和非仪器的误差，即，背反射的重叠效应和计算机分析的不适当建模。提出了分别检测不同来源的仪器误差的方法，其依据是在理想对准的RE中，输出信号应仅由直流分量组成，以实现完美的圆极化。在这种情况下，旋转频率的残余AC分量应归因于光束的小缠绕与由偏振棱镜处的小偏差、光路中的部分阻塞或合成分析器旋转的其他机械来源引起的不均匀检测器灵敏度的组合。其他与偏振相关的来源，例如分析棱镜的偏振灵敏度，导致AC分量的频率加倍。为了校正四分之一波片的非理想特性，提出了一种不需要波片的情况下测量相移和相对振幅透过率的新方法。通过这些修正，用区域消光差估算的剩余误差减小到1/20。在测量数据中，研究了背反射误差和垂直于薄膜表面的折射率不均匀性的影响。背反射误差被发现是成比例的剩余椭圆在反射条件下的完美的线性偏振周期性地观察作为波长的函数。在此条件下，不均匀性误差可以定量地测量为与具有裸衬底的软管的方位角的偏差。

This project aims to achieve overall accuracy of 0.1% of a rotating analyser ellipsometer (RE) by developing an alignment method to achieve 0.02% precision with production and use of a perfect circular polarization.Sources of errors in ellipsometry measurements have been attributed to those of instrumental and also of non-instrumental, i.e., the overlapping effect of back reflection and the inappropriate modelling of computer analysis. Procedures were developed for separately detecting the instrumental errors of various origins, which relies upon that in the ideally aligned RE, the output signal should be composed solely of DC component for the perfect circular polarization. In this condition, the residual AC components of the rotation frequency should be attributed to a small winding of a beam combined with uneven detector sensitivity caused by small deviation at the polarizing prism, partial obstruction in the optical path, or other mechanical origin synthesizing to the rotation of the analyser. Other polarization-related origins such as a polarization sensitivity of the analyser prism result in the AC components of doubled frequency. For the correction of imperfect characteristics of the quarter-wave plate, a new method has been developed to measure the phase shift and the relative amplitude transmittance without dismounting the plate. With these corrections, the residual errors estimated by zone extinction differences were reduced to a level of 1/20.The effects of the back reflection errors and of inhomogeneity of a refractive index normal to the thin film surface have been studied in the measured data. The back reflection error was found to be proportional to the residual elliptically at the reflection conditions of perfect linear polarizations observed periodically as a function of a wavelength. At these condition, the inhomogeneity error was able to be measured quantitatively as the deviations of the azimuthal angles from hose with a bare substrate.