Surface Profiling by Analysis of White-light Interferograms in the Spatial Frequency Domain

TLDR

The study presents a scanning white‑light interferometer designed for high‑precision surface structure analysis. The instrument scans the object perpendicular to its surface, records interferograms at each image point, transforms them into the spatial‑frequency domain, extracts surface height from the complex phase versus frequency, and constructs a complete 3‑D image from the height data and coordinates. The device achieves measurement repeatability better than 0.5 nm r.m.s.

Abstract

Abstract We describe a scanning white-light interferometer for high-precision surface structure analysis. Interferograms for each of the image points in the field of view of the instrument are generated simultaneously by scanning the object in a direction perpendicular to the object surface, while recording detector data in digital memory. These interferograms are then transformed into the spatial frequency domain and the surface height for each point is obtained by examination of the complex phase as a function of frequency. The final step is the creation of a complete three-dimensional image constructed from the height data and corresponding image plane coordinates. The measurement repeatability is better than 0·5 nm r.m.s. for a surface height range of 100 μm.