Time-dependent exposure dose of hydrogen silsesquioxane when used as a negative electron-beam resist

Hydrogen silsesquioxane (HSQ) is used as a high-resolution, negative-tone, inorganic electron-beam resist for use in nanoimprint lithography. Previous studies show that 1week long exposure delay in air decreases sensitivity and enhances the contrast of HSQ [F. C. M. J. M. van Delft, J. Vac. Sci. Technol. B 20, 2932 (2002)]. In this work, the authors report that the electron-beam dose required for high-resolution (sub-50-nm) HSQ patterning is shown to be very sensitive to the time the sample has been at room temperature. For example, a sample written with nanoscale features at constant e-beam dose will increase in size approximately 66% per hour of time at room temperature. The minimum feature size for a given dose depends on the ambient conditions the sample was stored in (air, nitrogen, vacuum). Samples stored in vacuum are not exempt from the feature broadening. Long e-beam writing times for large-area patterning of nanoscale features will likely suffer from this time dependence unless the exposure dose is varied during the e-beam writing. The experiments relating the various ambient conditions and the minimum feature size under dose control are presented.