Exposure of Hydrogen Silsesquioxane in Electron Beam Lithography

Hydrogen silsesquioxane (HSQ) offers high-resolution patterning capabilities in electron beam lithography. However, electron scattering within the resist remains challenging to detect, complicating the process control. Since previous research primarily focused on minimizing forward scattering by employing thin resist layers, this work specifically investigates scattering behavior using a thick HSQ resist (∼1 μm). By observing the residual resist of the HSQ nanopillars, the broadening trajectories of the electron beam due to forward scattering at various voltages are experimentally confirmed. Forward electron scattering generates a ring of residual resist surrounding nanopillars, with the residue shifting downward as the beam voltage increases. Backscattering electrons lead to residual resist in unexposed regions and at the nanopillar base. Increasing the developer concentration and extending the development duration effectively eliminates the scattering-induced residual resist, enabling steep HSQ nanopillars with a high aspect ratio (∼5) at 20 keV. The underlying exposure and development mechanisms are analyzed. From a practical perspective, the plasma etching performance of HSQ nanopillars is studied under gases (SF₆/O₂ and SF₆/C₄F₈) to fabricate silicon nanopillars. This research contributes to an in-depth analysis of the electron scattering behavior in HSQ resists, offering valuable insights for photoresist synthesis and lithographic process optimization.