Quantifying reduced negative ion contributions in nano-confined SiO2 wet etching via reaction-pathway analysis

Wet chemical processing in nano-confined geometries is increasingly required for advanced device fabrication, where the etching rate (ER) of SiO 2 is consistently lower than that of blanket films. Although electric double-layer (EDL) overlap has often been invoked to explain this behavior qualitatively, a quantitative, pathway-resolved understanding has been lacking. Here, we present a reaction-pathway analysis framework to quantify confinement-induced etching-rate suppression. By extending the classical Knotter model for dilute-HF etching with an additional OH − -driven dissolution pathway, we reproduce ER behavior across a wide pH range (−1 to 6) under NaOH-based pH adjustment. Statistical fitting of reaction constants ( k 0 − k 3 ) and a surface-speciation parameter ( K 3 ) to ER–pH data for both blanket and 3–10 nm confined SiO 2 structures enables decomposition of individual pathway contributions. The analysis indicates that negatively charged pathways (HF 2 − and OH − ) are significantly reduced under nano-confinement, whereas the neutral H 2 F 2 -driven pathway is comparatively less affected. These trends are consistent with changes in the availability or transport of anionic species in confined geometries, potentially associated with electrostatic effects such as EDL overlap, although contributions from geometric hindrance and specific adsorption cannot be independently ruled out. The fitted kinetic parameters should therefore be interpreted as effective quantities that incorporate multiple confinement-related effects. The model reproduces the ER–pH relationships with small residual errors. The root mean square error (RMSE) is 0.33 Å s −1 for the blanket dataset and 0.22, 0.13, and 0.28 Å s −1 for the 10 nm, 5 nm, and 3 nm confined structures, respectively, indicating good agreement across all conditions relative to the overall ER range. The proposed framework provides quantitative insight into wet etching behavior in nano-confined environments and offers practical guidance for selecting chemistries and pH windows to mitigate etching-rate loss in nanoscale fabrication processes.