Sub-10nm resolution after lift-off using HSQ/PMMA double layer resist

Hydrogen silesquioxan (HSQ) is a well-investigated negative tone inorganic resist [1,2] which is known for its capabilities for high resolution electron beam lithography (EBL) and its stability against dry etching [3]. In this paper, we introduce a process to create dense structures by EBL utilizing a layer of poly-methyl-methacrylate (PMMA) as sacrificial layer beneath a HSQ layer. The sacrificial layer allows a simple lift-off process to remove the HSQ with organic solvents and thus avoids the use of hydrofluoric acid (HF) containing etchants, which is the commonly used HSQ remover [4]. The described double layer resist system allows patterning on substrates that are not HF compatible such as glass or oxide compounds, achieving a high resolution down to the sub-10nm regime. Despite the use of a double layer resist, this process is applicable for arbitrarily large areas due to the remaining PMMA underneath the HSQ and the avoidance of undercuts.