基于红外干涉法的碳化硅外延层厚度测量研究

Research on Measurement of Silicon Carbide Epitaxial Layer Thickness Based on Infrared Interferometry

摘要: 为满足第三代半导体碳化硅(SiC)外延层厚度高精度、无损、标准化测量需求，解决传统红外干涉法因双光束近似、固定折射率假设与单入射角拟合带来的系统误差大、稳定性不足等关键问题，本文提出一种融合光学干涉模型、Cauchy折射率色散和Drude折射率色散模型修正与双入射角联合非线性拟合的厚度反演方法。研究构建单层反射双光束干涉模型与更贴近真实物理过程的Fabry-Pérot多光束干涉模型，引入Cauchy色散方程精准描述折射率随波长的变化规律，依托Python完成光学建模、干涉仿真与数据处理。实验采用10˚与15˚双入射角红外反射光谱进行联合拟合，显著抑制层内多次反射、折射率色散、光谱噪声及基线漂移对测量结果的影响。结果表明，消除多光束干涉系统误差后，SiC外延层厚度为8.8037 μm，硅外延层厚度为4.6441 μm；传统双光束模型计算结果为8.0000 μm，量化验证了多光束效应对厚外延层测量的系统性偏差。误差与稳定性分析显示，Fabry-Pérot多光束模型拟合精度更高、残差更小，决定系数R²大于0.99，在不同初始值下均稳定收敛，厚度相对偏差小于0.5%。该方法无损、快速、可标准化，适用于SiC、Si等半导体外延层检测，可推广至其他第三代半导体材料的无损厚度测量，为SiC器件研发、工艺控制与产业化提供高精度技术支撑。

Abstract: To meet the demands for high-precision, non-destructive and standardized thickness measurement of silicon carbide (SiC) epitaxial layers of third-generation semiconductors, and solve the key problems of large systematic errors and insufficient stability existing in traditional infrared interferometry caused by two-beam approximation, fixed refractive index assumption and single-incident-angle fitting, this paper proposes a thickness inversion method integrating optical interference model, Cauchy refractive index dispersion and Drude Refractive Index Dispersion Model correction and dual-incident-angle joint nonlinear fitting. This study constructs a single-layer reflective two-beam interference model and a Fabry-Pérot multi-beam interference model closer to real physical processes, introduces the Cauchy dispersion equation to accurately describe the variation rule of refractive index with wavelength, and completes optical modeling, interference simulation and data processing based on Python. In the experiment, infrared reflectance spectra at incident angles of 10˚ and 15˚ are adopted for joint fitting, which greatly suppresses the effects of intra-layer multiple reflections, refractive index dispersion, spectral noise and baseline drift on measurement results. The results show that after eliminating the systematic error of multi-beam interference, the thickness of SiC epitaxial layer is 8.8037 μm and the thickness of silicon epitaxial layer is 4.6441 μm, while the calculation result of traditional two-beam model is 8.0000 μm, which quantitatively verifies the systematic deviation caused by multi-beam effect in the measurement of thick epitaxial layers. Error and stability analysis indicates that the Fabry-Pérot multi-beam interference model has higher fitting accuracy and smaller residuals with the coefficient of determination R² greater than 0.99, and it can converge stably under different initial values with relative thickness deviation less than 0.5%. Featuring non-destructiveness, rapidity and easy standardization, this method is suitable for the detection of SiC, Si and other semiconductor epitaxial layers, and can be extended to non-destructive thickness measurement of other third-generation semiconductor materials, providing high-precision technical support for the research and development, process control and industrialization of SiC devices.