Hydrogen silsesquioxane bilayer resists—Combining high resolution electron beam lithography and gentle resist removal

Hydrogen silsesquioxane (HSQ) is one of the leading resists for high resolution electron beam lithography. For example, lines and spaces with 12 nm pitch are reported in ultrathin HSQ. However, to take advantage of this HSQ capability for functional devices, the pattern defined in the resist has to be transferred to the underlaying substrate—either by etching or material deposition. The common remover for HSQ is hydrofluoric acid (HF), which is not suitable for all substrates. To avoid HF as remover, bilayer resist systems were developed by different groups combining the high resolution capabilities of HSQ with the possibility to remove the resist with an organic solvent. In this paper, three different types of sacrificial layers including chrome, Novolak resin, and poly methyl methacrylate are reviewed and compared.