目的：联合使用光谱型椭偏仪( SE)和分光光度计,精确测定超薄四面体非晶碳薄膜( ta-C)的光学常数。方法由于该薄膜的厚度对折射率、消光系数有很大的影响,仅采用椭偏参数拟合,难以准确得到该薄膜的光学常数,椭偏法测定的未知参数数量大于方程数,椭偏方程无唯一解。因此,加入透过率与椭偏参数同时进行拟合(以下简称SE+T法),以简单、快速、准确地得到该薄膜的光学常数。结果薄膜具有典型的非晶碳膜特征,SE和SE+T两种拟合方法得到的光学常数具有明显的差异,消光系数k在可见以及红外区最大差值可达0.020,紫外区最大的偏差约为0.005；折射率n在500 nm 波长以上最大差值为0.04,在紫外光区和可见光区两种方法得到的n趋于一致。联用时的拟合结果具有更好的唯一性,而且拟合得到的光学常数变得平滑。结论椭偏与分光光度计联用适合精确测定测量范围内的超薄四面体非晶薄膜的光学常数。
Objective To explore accurate measurement of optical constants of the ultrathin tetrahedral amorphous carbon ( ta-C) films by combined usage of spectral ellipsometry ( SE) and spectrophotometry. Methods As the amount of unknown parameters determined by ellipsometry method was larger than the number of equations and the ellipsometric equations had no unique solution, the accurate determination of the optical constants of the ultrathin ta-C film accurately was difficult when independently using ellip-sometric parameters for fitting due to the strong statistical influence of the film thickness on refractive index and extinction coeffi-cient. Therefore, in this paper, ellipsometric parameters and transmittance ( hereinafter referred to as SE+T) were simultaneously fitted to obtain optical constants more easily and rapidly. Results The results showed that the film had typical characteristics of amorphous carbon films. There were obvious differences in optical constants obtained by SE and SE+T. The maximum difference value of extinction coefficient k was up to 0. 020 in the visible and infrared area and was 0. 005 in the ultraviolet area. The maxi-mum difference value of the refractive index n was 0. 04 at wavelengths above 500 nm. The n value tended to be consistent by the two methods in the ultraviolet and visible area. The fitting results had better uniqueness by SE+T and the fitted optical constants were smooth. Conclusion This method of SE+T is suitable for accurate measurement of optical constants of ultrathin ta-C films within measurement range.
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