Research on Multi-Traceability-Chain Comparison of Film Thickness Values Based on SiO2 Thin Films

Nanoscale film thickness metrology suffers from inconsistent results across instruments operating on different physical principles, which undermines measurement reliability and traceability. For single-wavelength ellipsometry in particular, inherent coupling between film thickness and refractive index causes inversion ambiguity, hindering rigorous metrological comparison with metrological atomic force microscopy (AFM). To address this, we propose a stepped SiO2 thin film fabricated by atomic layer deposition and wet etching as a transfer standard for cross-method comparison. The metrological AFM measures step height traceable to the SI meter definition via three-axis laser interferometry, while the ellipsometer derives thickness from ellipsometric parameters (Ψ, Δ) traceable to an iodine-stabilized He-Ne laser. A multi-sample global fitting strategy is adopted to resolve the underdetermined inversion problem. For three samples of ~105 nm, ~492 nm and ~955 nm, the two methods show relative deviations below 0.5%, with a normalized deviation EN of 0.26 for the 955 nm sample, well below the acceptance threshold of 1. Results confirm the stepped film as an effective transfer standard, providing a practical framework for value unification in nanoscale film thickness metrology.