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Nondestructive three-dimensional topography of high-aspect ratio structures presents significant challenges, particularly in accurately capturing the bottom topography. Here, a sample-induced aberration-compensable near-infrared coherence scanning interferometry is proposed, with the capacity of measuring the bottom of high-aspect ratio structures and reconstructing full three-dimensional topographies. While near-infrared light penetrates the silicon to boost probe throughput, the modulation by high-aspect ratio structures defocuses the probe at the bottom. To comprehend the modulation characteristics and devise solutions, the finite element method and angular spectrum diffraction modeling are combined to analyze the high-aspect ratio sample-induced modulation, and then, a solution is devised to refocus the probe. Consequently, an aberration detection optical path integrated into the coherence scanning interferometry system is constructed. By utilizing the measured aberrations as feedback, an aberration-compensating wavefront corrector is then introduced in the test arm to refocus the probes to the bottom. The proposed method surpasses the restrictions associated with the aspect ratio in three-dimensional topography. Experiments on ∼200 μm-deep and ∼20:1-aspect ratio trenches showcase simultaneous high microscopic lateral resolution and interferometric vertical precision for accurate three-dimensional high-aspect ratio trench metrology.
Ma et al. (Tue,) studied this question.