Optical Constants and Thickness Testing of Films Based on Reflection Spectroscopy
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摘要:
薄膜的光学常数(折射率、消光系数)和厚度决定了镀膜零件的光学性能，因此根据实际条件掌握薄膜的光学常数和厚度是膜系结构设计和性能优化的重要环节。本文采用傅里叶红外光谱仪测试薄膜样品的反射光谱曲线，通过单纯形优化算法拟合反射光谱曲线，借助不同色散模型，构建目标优化函数，获得薄膜光学常数和厚度，拟合结果与采用椭偏仪测试的结果具有较好的一致性。将拟合得到的薄膜光学参数及厚度代入反射率理论计算模型，通过理论计算模型得到的反射率曲线和实验测试曲线吻合良好，折射率测试结果与计算结果的最大相对误差小于1.8%，厚度测试结果的相对误差不大于0.4%，考虑消光系数的反射光谱拟合曲线与测试曲线相对误差的最大值小于2%。该方法只需测量薄膜的反射光谱曲线，通过计算就能得到薄膜的光学常数及厚度。该方法测试计算简单、精度高、适用范围广，对光学薄膜结构设计、优化和加工具有一定的实际应用价值。
Abstract:The optical constant (refractive index, extinction coefficient) and thickness of the film determine the optical properties of the coated part, so mastering the optical constant and thickness of the film according to the actual conditions is an important part of the film structure design and performance optimization. In this study, a Fourier transform infrared spectrometer was used to measure the reflectance spectrum curve of the sample. The target optimization function was constructed with the help of a different dispersion model, the simplex optimization algorithm was fitted to the reflectance spectrum curve, and the optical constant and thickness of the thin film were obtained using the target optimization function. The fitted optical constant and thickness of the thin film agree with the ellipsometer test results. When the inverted optical parameters and thickness of the thin film were incorporated into the theoretical reflectance calculation model and the reflectance curve obtained by the theoretical calculation model was in good agreement with the experimental test curve, the maximum relative error of the refractive index was less than 1.8%, the maximum relative error of thickness was less than 0.4%, and the maximum relative error of reflectance was less than 2%. This method only requires the measurement of the reflectance spectrum curve, and the optical parameters of the thin film can be obtained through calculations. This method has simple testing calculations, high accuracy, and a wide application range. This has important practical applications in structural design, optimization, and machining of optical thin films.
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Keywords:
- optical thin film /
- reflection spectrum /
- refractive index /
- thin film thickness
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图 3 Ge/ZnSe薄膜折射率、消光系数曲线
Figure 3. Refractive index, extinction coefficient curves of Ge/ZnSe thin film
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图 5 YbF3/Ge薄膜折射率、消光系数曲线
Figure 5. Refractive index, extinction coefficient curves of YbF3/Ge thin film Wavelength λ/μm Reflectivity/%
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图 7 DLC/Ge薄膜折射率、消光系数曲线
Figure 7. Refractive index, extinction coefficient curves of DLC/Ge thin film
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图 9 Ge/ZnSe膜折射率相对误差曲线
Figure 9. Relative error of refractive index of Ge/ZnSe thin film
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图 13 YbF3/Ge膜折射率相对误差曲线
Figure 13. Relative error of refractive index of YbF3/Ge thin film
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