Non-integral depth measurement of high-aspect-ratio multi-layer microstructures using numerical-aperture shaped beams

This work presents a new optical metrology technique for accurate depth measurement of individual high-aspect-ratio (HAR) multi-layer microstructures with high spatial resolution and signal-to-noise ratio (SNR). To resolve the limitations of existing optical metrology techniques, light shaping with high light efficiency is optimized using numerical-aperture controlled laser beams. Experimental tests evidenced a 28-fold improvement in SNR for measuring large-depth structures when compared with measurements obtained using traditional broadband incoherent illumination. More importantly, instead of integral measurement characteristics currently limited by conventional spectral reflectometry or scatterometry, non-integral depth measurement of an individual microstructure from densely spaced microstructures such as through-silicon vias (TSV) and redistribution layers (RDL) can be realized using the developed optical measuring system with desired numerical aperture and field of view achieved simultaneously. As demonstrated by the measurement of a single submicron structure with linewidth as small as 0.6 mu m and an aspect ratio of 5, the precision of depth measurement can be kept within a few nanometers.

Automated summary

This work introduces a new optical metrology technique that enables accurate depth measurement of high-aspect-ratio multi-layer microstructures with high spatial resolution and signal-to-noise ratio. By optimizing light shaping using numerical-aperture controlled laser beams, the limitations of existing optical metrology techniques are overcome. Experimental tests show a 28-fold improvement in SNR for measuring large-depth structures compared to traditional broadband incoherent illumination. The developed optical measuring system allows for non-integral depth measurement of densely spaced microstructures, such as through-silicon vias and redistribution layers, with desired numerical aperture and field of view achieved simultaneously. The precision of depth measurement can be maintained within a few nanometers, as demonstrated by measuring a single submicron structure with a linewidth of 0.6 μm and an aspect ratio of 5.