Liquid-Cell Transmission Electron Microscopy Observation of Two-Step Collapse Dynamics of Silicon Nanopillars on Evaporation of Propan-2-ol: Implications for Semiconductor Integration Density

Miniaturization of semiconductor devices has made structures more fragile, leading to potential collapses due to capillary forces during drying after wet cleaning. This has hampered the integration of transistors according to Moore's law. We have developed a method for preparing nanopillars in a liquid cell and have successfully observed their collapse by means of a crosssectional view in transmission electron microscopy. The dynamics of collapse as a result of capillary interactions involve two steps. First, the nanopillars collapse due to an imbalance in capillary forces caused by a difference in liquid levels at the gas-liquid interface. Second, a liquid pool formed between nanopillars maintains the collapsed state of the nanopillars through surface tension. The nanopillars recover on reimmersion in the liquid after the collapse. This method is effective, and is expected to contribute to the continued development of miniaturization and three-dimensionality of semiconductors.