利用单波长椭偏仪对各向异性薄膜光学常数和欧拉角的研究

基于椭偏测量原理和4×4矩阵法原理，提出了利用单波长椭偏仪在光轴平行于薄膜表面方向上测量各向异性薄膜的薄膜参数(包括双折射率、厚度及欧拉角)的方法.通过转动待测样品90°的方法，得到2组椭偏参数，利用反演算法对2组椭偏参数进行反演，得到各向异性薄膜的4个薄膜参数；采用数值模拟分析了入射角、薄膜厚度、欧拉角及其定位误差对测量结果的影响；实验测量了光轴平行于样品表面的各向异性聚酰亚胺薄膜样品在转动前后的椭偏参数，并进行反演.结果表明:该方法提出的算法反演稳定性好、精度高；该方法测得各向异性薄膜的寻常光折射率、非寻常光折射率、厚度以及欧拉角的精度分别达到0.000 1、0.000 1、0.1 nm及0.03°；寻常光折射率、非寻常光折射率、厚度的最大测量误差分别为0.001 2，0.004 4以及4.57 nm；该方法具有较好的测量稳定性、自洽性及可靠性.文中提出的方法具有测量过程简单、对实验仪器要求低的优点，拓展了单波长椭偏仪的测量范围，提出了各向异性薄膜参数的测量方法，具有实际应用意义.

A Study of the Optical Constants and Euler Angle of Anisotropic Thin Film with the Single-wavelength Ellipsometer

Based on the principle of ellipsometry and the 4×4 matrix method, a way of measuring the parameters of anisotropic films whose optical axis is parallel to the surface with the single-wavelength ellipsometer is proposed, the parameters including birefringence, thickness and Euler angle. Two sets of ellipsometric parameters can be obtained by rotating the sample at 90°, and four film parameters of the anisotropic film can be obtained with the inversion algorithm to invert two sets of ellipsometric parameters.The effects of incident angle, film thickness, Euler angle and its rotation error on measurement accuracy are discussed with numerical simulation. The ellipsometric parameters of the polyimide film whose optical axis parallels its surface are measured and inverted. The results show that the algorithm has good stability and high precision and the ordinary refractive index, extraordinary refractive index, thickness and Euler angle are 0.000 1, 0.000 1, 0.1 nm and 0.03° respectively. The maximum measurement errors of ordinary refractive index, extraordinary refractive index and thickness are 0.001 2, 0.004 4 and 4.57 nm respectively. This method has good measurement stability, self-consistency and reliability as well as the advantages of simple measurement process and low requirement for instruments. This method extends the measurement range of single-wavelength ellipsometer and the way of measuring anisotropic film, so it has practical significance.