# Meta-device for sensing subwavelength lateral displacement

## TL;DR

A new method using two-photon interference and metasurfaces improves lateral displacement measurement for lithography with fewer photons and higher speed.

## Contribution

A novel two-photon state transverse displacement measurement method using polarization gradient metasurfaces is introduced.

## Key findings

- The new method reduces detected photons to 3% of classical methods while maintaining precision.
- The approach is suitable for next-generation lithography with faster acquisition times.
- The method uses a polarization gradient metasurface for high-speed nanoscale alignment.

## Abstract

Accurate transverse displacement measurement is essential for precise mask-to-wafer positioning in lithography. While lateral displacement metrology has achieved nanometer-level precision, the limitations imposed by coherent state and grating challenge in-situ measurement speed and precision. Here, we introduce a two-photon state transverse displacement measurement method utilizing a polarization gradient metasurface by employing two-photon state interference. Compared with the classical method, our new method can experimentally reduce the number of detected photons to around 3% with equivalent precision. These attributes make the two-photon state polarization gradient metasurface approach highly suitable for integration with semiconductor lithography processes and show its promise in realizing equivalent measurement precision within notably shorter acquisition durations, providing a robust solution for next-generation transverse displacement measurement requirements.

Two-photon-enhanced lateral displacement metrology with polarization gradient (geometric phase) metasurfaces achieves 97% photon number reduction for high-speed nanoscale mask-wafer alignment in next-generation lithography.