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Terahertz time-domain spectroscopy (THz-TDS) allows broadband noninvasive measurement of the optical parameters of various materials in the THz domain. The measurement accuracy of these parameters is highly influenced by the difficulty in distinguishing THz signals from unwanted signals such as noise, signal fluctuation, and multiple echoes, which directly affects material identification and characterization efficiency. We introduce a novel method that provides effective extraction and separation of THz signals from such undesired effects. The proposed algorithm was assessed through experiments that presented enhancement in material parameter evaluation, such as the decomposition of the sample-induced echoes (SIEs) from the complex THz sample signal with near-zero extraction error. Improved precision ( ± 0.05 μ m) was achieved in the determination of the sample thickness compared to that of the mechanical method ( ± 10 μ m). Furthermore, we could infer from the component concentration measurement results of a compound sample (44.2 % decrease in the root mean square concentration error) that the material parameter calculation accuracy had improved, proposing a means to enhance the ultimate nondestructive material evaluation performance.

Accurate and non-destructive measurement of thin layer thickness is critical for ensuring the quality and performance of microelectronic devices. In this study, terahertz time-domain spectroscopy (THz-TDS) was used to measure the combined thickness of a silicon wafer and its deposited thin layer without requiring prior knowledge of the individual material properties. The multi-reflected THz signals from the Si wafer were utilized to accurately calculate the actual thickness and optical properties with a 0.19% error. In the reflection measurement, the variation of optical properties was measured according to the thickness of the deposition through the quartz chamber window. To overcome the intrinsic overlapping of the pulse signal through the quartz chamber window, the detection time of unwanted signals was calculated theoretically, and the inspection conditions such as quartz window thickness and distances between the wafer and window were optimized for accurate measurement with THz-TDS. Based on these results, the accuracy of thickness prediction in the thin layer was confirmed with 4.2% of an error.