Understanding into the microstructure and diffusion behaviors of water removal in nanopores of wafer by supercritical carbon dioxide: Experiment and molecular dynamics simulation

In the fabrication of semiconductor devices, especially wafer processing, drying process constitutes a critical processing step. The continuing reduction of critical dimensions in wafer manufacturing has rendered structural collapse (deformation or bending) induced by conventional wet processing techniques an increasingly severe issue. Supercritical carbon dioxide (scCO₂), owing to its absence of surface tension, demonstrates significant potential as an effective displacement agent and drying medium for nanostructure of wafer. However, the understanding of the underlying drying mechanisms for the residual water in the nanostructure of wafer remains insufficient. Herein, the microstructure and diffusion behaviors of residual water removal in silicon nanopores of wafers in the scCO₂ medium affected by various concentrations of isopropanol (IPA) co-solvent using equilibrium- and non-equilibrium molecular dynamics simulations were studied in details. The increased amount of IPA contributes to the better dispersion of water droplet in the scCO₂ with lower energy barrier of water dissolution. The residual water molecules undergo overall displacement and swelling behaviors during the scCO₂ fluid flooding process. The experimental results indicate that with the increasing treatment time and additive amount of IPA, the residual salt concentrations in the microscale structures less than 10 μm, even below the detection limit of Inductively-Coupled Plasma Optical Emission Spectrometry (ICP-OES), which confirms the effectiveness of supercritical drying of wafer nanopatterns. Furthermore, the drying efficiency shows distinct feature-size dependence. Overall, these findings are of paramount importance to provide fundamental molecular-level insights into water removal processes in micro/nano structures of wafer during drying by scCO₂.