Formation of 15 nm scale Coulomb blockade structures in silicon by electron beam lithography with a bilayer resist process

We have formed Coulomb blockade structures with widths of 15–30 nm in silicon-on-insulator (SOI) by electron beam lithography (EBL) in a bilayer resist process. The bilayer structure consisted of HSQ (hydrogen silsesquioxane) and AZ organic resist. The organic resist protects the buried oxide and allows removal of exposed HSQ features with hydrofluoric acid (HF). Measurements at 4.2 K show pronounced Coulomb blockade signatures for 15 nm wide wires. This bilayer resist process provides direct lithographic access to 15 nm level features in SOI without the need for size reduction by oxidation.