Dimension and process effects on the mechanical stability of ultra-small HSQ nanopillars

The demand for ever-smaller devices increases with the development of the semiconductor industry. High-resolution patterning based on lithography is significant to fabricate ultra-small nanostructures in various nanodevices. With the minimization of feature size down to nanometric scale, it is challenging to reliably define ultra-small features and structures through lithographic approaches. The ultra-small resist structures defined by lithography approaches usually suffer from mechanical instability behaviors during the development and drying process. The stable mechanical behaviors of lithography-defined resist nanopatterns are the important issue for reliable fabrication. Exploring the mechanical stability of resist patterns is of great importance both scientifically and technologically. Hydrogen silsesquioxane (HSQ) is a high-resolution negative-tone electron-beam resist for sub-10-nm fabrication. But, the ultra-small electron-beam exposed HSQ resist structures usually suffer from collapse and displacement after the development process. Hence, it is essential to understand the stability behavior of HSQ resist nanostructures to reliably fabricate various nanodevices. But, a systematic study of the stability behavior of HSQ is still lacking. To address this issue, we exposed the HSQ nanopillars on different substrates and dried them using different drying methods to probe the factors of critical dimensions, substrate adhesion, and dry methods for reliable HSQ nanopillars fabrication in this work. Through the analysis of experimental data, we found the adhesion dominates the mechanical stability of HSQ nanopillars at the ultra-small scale. By using finite element analysis, we systematically explored the role of the capillary effect in the two main unstable mechanics behaviors (collapse and displacement). To suppress the capillary forces, we optimized the drying process with the use of CO₂ supercritical drying. We further provided an effective and facile method through spin-drying in the atmosphere to improve the stability of lithography-defined HSQ pillars.