A White Light Spectral Interferometric Demodulation Method Based on Frequency Domain Solving and Model Matching

White-light interferometry (WLI) is widely used for thin-film thickness metrology due to its non-destructive and high-speed characteristics. Yet conventional data-processing pipelines struggle to balance accuracy and computational efficiency. We introduce a Collaborative Spectral–Phase optimization (C-SP) algorithm that enables rapid, high-precision thickness evaluation of single-layer opaque films. C-SP adopts a two-stage coarse-to-fine framework: a frequency-domain coarse estimation first narrows the parameter space, followed by adaptive local refinement via an improved stochastic parallel gradient descent. The adaptive search window effectively mitigates local stagnation while concentrating computation on the most probable solution region. Experimental validation on SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films demonstrates a repeatability below 0.49 nm, a 3σ value under 1.46 nm, and a computation time less than 0.19 s. This method only requires the measurement of the interference spectrum of the film, and the thickness of the film can be calculated. The method combines speed, precision, and broad applicability, providing a practical tool for thin-film structural characterization, process optimization, and in-line fabrication control.