Scanning in coherent Fourier scatterometry using Fresnel zone plate projection on a digital micromirror device

Abstract

We present a digital micro-mirror device (DMD)-enabled scan head for coherent Fourier scatterometry (CFS) that performs lateral scanning without macroscopic moving parts, while maintaining a diffraction-limited probe. A binary Fresnel zone plate (FZP) is displayed and translated on the DMD to steer a single focused spot across the sample, providing an electronically programmable alternative to scanning using piezo-based translation devices. To the best of our knowledge, this is the first published CFS implementation in which a DMD is the primary lateral scanning element. Furthermore, the DMD programmability is used to compensate for the scan-position-dependent aberrations using an iterative optimisation algorithm. Across a 400 × 200 DMD-pixel scan area, the peak-intensity coefficient of variation improves from 39.4% (uncorrected) to 16.1% (after correction) and to 4.47% with additional power normalisation, demonstrating substantially improved probe uniformity. Finally, we demonstrate particle detection on a Si wafer with 1 µm polystyrene latex particles, achieving an signal-to-noise ratio of 16.04 ± 1.11 dB. The results establish DMDFZP scanning with integrated aberration correction as a compact, fast, and scalable CFS architecture, with a clear pathway to higher throughput via multi-spot parallelisation.