In-situ non-contact monitoring of photoresist thickness and degree of cure using terahertz time-domain spectroscopy

IF 4.5 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING

Ndt & E International Pub Date : 2025-08-20 DOI:10.1016/j.ndteint.2025.103530

Sang-Il Kim , Hak-Sung Kim

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Abstract

In this work, a terahertz time-domain spectroscopy (THz-TDS) system was used to measure the thickness and refractive index of the photoresist during the photolithography process. The THz-TDS system was configured in a reflection mode to inspect the photoresist. The time-domain THz waves reflected from the photoresist were analyzed in the frequency-domain using a Fourier transform. The amplitude and phase information of the frequency-domain THz waves were expressed as functions of the photoresist's thickness and refractive index using Fresnel equations. Numerical analysis was used to simultaneously determine the thickness and refractive index of the photoresist. The measurements obtained by the THz-TDS system were compared with spectroscopic ellipsometry, white light reflectance spectroscopy (WLRS), and scanning electron microscopy (SEM). The thickness and degree of curing of the photoresist were monitored in real time without contact, with a final-stage thickness difference of 12.3 % and a Pearson correlation coefficient up to 0.72 between THz monitoring and conventional methods.

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利用太赫兹时域光谱对光刻胶厚度和固化程度进行现场非接触监测

本文采用太赫兹时域光谱（THz-TDS）系统测量光刻过程中光刻胶的厚度和折射率。THz-TDS系统配置为反射模式以检测光刻胶。利用傅里叶变换对光刻胶反射的时域太赫兹波进行频域分析。利用菲涅耳方程将频率域太赫兹波的振幅和相位信息表示为光刻胶厚度和折射率的函数。采用数值分析方法同时确定了光刻胶的厚度和折射率。将太赫兹- tds系统测量结果与椭圆偏振光谱、白光反射光谱（WLRS）和扫描电子显微镜（SEM）进行了比较。通过无接触实时监测光刻胶的厚度和固化程度，太赫兹监测与常规方法之间的最后阶段厚度差异为12.3%，Pearson相关系数高达0.72。

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来源期刊

Ndt & E International 工程技术-材料科学：表征与测试

CiteScore

7.20

自引率

9.50%

发文量

121

审稿时长

55 days

期刊介绍： NDT&E international publishes peer-reviewed results of original research and development in all categories of the fields of nondestructive testing and evaluation including ultrasonics, electromagnetics, radiography, optical and thermal methods. In addition to traditional NDE topics, the emerging technology area of inspection of civil structures and materials is also emphasized. The journal publishes original papers on research and development of new inspection techniques and methods, as well as on novel and innovative applications of established methods. Papers on NDE sensors and their applications both for inspection and process control, as well as papers describing novel NDE systems for structural health monitoring and their performance in industrial settings are also considered. Other regular features include international news, new equipment and a calendar of forthcoming worldwide meetings. This journal is listed in Current Contents.