基于FFT的厚膜反射法厚度提取的实用评估
Practical Evaluation of FFT-Based Thickness Extraction for Thick-Film Reflectometry
AI总结：
该研究对比FFT、LRZ等厚膜厚度提取方法，发现FFT重复性好但精度不足，LRZ精度更高，指出频谱泄漏是FFT偏差原因，凸显零交叉法在厚膜计量的优势。
AI中文摘要：
快速傅里叶变换（FFT）因简便性和计算效率被广泛应用于厚膜反射法中，但其在实际厚膜测量条件下的性能仅得到有限的实验评估。本研究采用生产晶圆上标称52μm介电薄膜的反射法测量数据，将FFT、线性化反射零交叉法（LRZ）与光学模型拟合进行对比，以白光干涉法（WLI）作为独立参考。尽管FFT展现出出色的重复性，但与WLI存在系统偏差（均方根误差RMSE=0.62μm），而LRZ显著提升了精度（RMSE=0.20μm）。模拟与理论分析表明，观测到的系统偏差与有限测量窗口及非整数条纹周期性导致的频谱泄漏一致。这些结果表明，出色的重复性不一定意味着高精度，并凸显了基于零交叉的方法在厚膜厚度计量中的优势。
英文摘要：
Fast Fourier transform (FFT) is widely used for thick-film reflectometry because of its simplicity and computational efficiency. However, its performance under practical thick-film measurement conditions has received limited experimental evaluation. In this work, FFT, Linearized Reflectance Zero-Crossing (LRZ), and optical model fitting were compared using reflectometry measurements from a nominal 52 μm dielectric film acquired on a production wafer, with White-Light Interferometry (WLI) serving as an independent reference. Although FFT exhibited excellent repeatability, it showed systematic deviation from WLI (RMSE = 0.62 μm), whereas LRZ significantly improved accuracy (RMSE = 0.20 μm). Simulations and theoretical analysis indicate that the observed systematic deviation is consistent with spectral leakage caused by finite measurement windows and non-integer fringe periodicity. These results demonstrate that excellent repeatability does not necessarily imply high accuracy and highlight the advantages of zero-crossing-based approaches for thick-film thickness metrology.
