# Fourier ptychographic coherence scanning interferometry for 3D morphology of high aspect ratio and composite micro-trenches

## TL;DR

A new imaging method improves 3D measurements of complex microstructures used in advanced manufacturing.

## Contribution

Fourier ptychographic coherence scanning interferometry (FP-CSI) is introduced as a transmissive CSI modality with enhanced resolution and SNR for high aspect ratio structures.

## Key findings

- FP-CSI achieves lateral resolution up to the incoherent diffraction limit.
- Accurate measurements of a 30:1 aspect ratio micro-trench and MEMS devices are demonstrated.
- FP-CSI maintains performance at trench bottoms without iterative phase retrieval.

## Abstract

Non-destructive and accurate characterization of high aspect ratio (HAR) and composite micro-trenches is critical for advanced microfabrication but remains a major challenge. Conventional coherence scanning interferometry (CSI), while widely adopted, suffers from low signal-to-noise ratio (SNR) and limited lateral resolution when applied to HAR and composite microstructures. Here, we present Fourier ptychographic coherence scanning interferometry (FP-CSI), the first transmissive CSI modality that integrates the aperture synthesis strategy of Fourier ptychographic microscopy with the quantitative phase-resolved capability of interferometry. FP-CSI enables robust three-dimensional morphology reconstruction with enhanced SNR and improved lateral resolution, without reliance on iterative phase retrieval. We demonstrate accurate measurements of a HAR micro-trench (300 μm depth, 30:1 aspect ratio) and micro-electro-mechanical system (MEMS) devices (aspect ratios 6:1–20:1). FP-CSI achieves lateral resolution up to the incoherent diffraction limit and maintains this performance even at trench bottoms. Owing to its fidelity, robustness, and non-destructive operation, FP-CSI provides a powerful new metrology platform for next-generation semiconductor inspection, precision manufacturing, and emerging micro-optoelectronic systems.

A transmissive Fourier ptychographic coherence scanning interferometry method provides accurate 3D morphology measurements of high aspect ratio and composite micro-trenches, enhancing both the signal-to-noise ratio and lateral resolution.