Supercritical CO₂ drying in nanoscale confinement: Molecular mechanisms and displacement efficiency

High-aspect-ratio nanostructures in semiconductor fabrication are highly susceptible to capillary-induced pattern collapse during drying, posing a serious challenge to structural integrity and device performance. Supercritical CO₂ (scCO₂) drying has emerged as an effective, low-damage alternative by displacing the organic solvent isopropanol (IPA). However, the molecular-level transport processes and displacement pathways under nanoscale confinement remain poorly understood. In this study, molecular dynamics simulations are employed to elucidate the microscopic mechanisms governing scCO₂–IPA displacement, with a focus on molecular diffusion, interfacial interactions, and local structural reorganization. The results reveal that the pressure dependence of displacement efficiency is governed by a competition between enhanced IPA dissolution and diffusion limitations arising from the increasing density of scCO₂. In the range of 8–20 MPa, higher pressure significantly facilitates CO₂ penetration into confined regions and accelerates IPA dissolution, thereby improving displacement efficiency. Beyond ∼20 MPa, however, the diffusivity of scCO₂ decreases sharply, leading to a marked plateau in displacement performance. Elevated temperature disrupts the local structural ordering of IPA and enhances the diffusivity of both CO₂ and IPA, resulting in a continuous increase in the displacement rate. This work provides molecular-level insight into the pressure- and temperature-dependent transport behaviors during scCO₂ drying and offers quantitative guidance for optimizing supercritical drying strategies for high-aspect-ratio semiconductor nanostructures. • MD simulations reveal the microscopic mechanism of scCO₂ displacing IPA. • Pressure controls drying through competing solubility and diffusion effects. • Temperature enhances displacement by increasing self-diffusion and weakening IPA structure. • Structural evolution and diffusion analysis clarify CO₂–IPA transport dynamics. • Findings guide optimization of scCO₂ drying for high-aspect-ratio nanostructures.