We investigate poly͑methylmethacrylate͒ ͑PMMA͒ development processing with cold developers ͑4-10°C͒ for its effect on resolution, resist residue, and pattern quality of sub-10 nm electron beam lithography ͑EBL͒. We find that low-temperature development results in higher EBL resolution and improved feature quality. PMMA trenches of 4-8 nm are obtained reproducibly at 30 kV using cold development. Fabrication of single-particle-width Au nanoparticle lines was performed by lift-off. We discuss key factors for formation of PMMA trenches at the sub-10 nm scale.

We demonstrate a guided self-assembly approach to the fabrication of DNA nanostructures on silicon substrates. DNA oligonucleotides self-assemble into "rafts" 8 x 37 x 2 nm in size. The rafts bind to cationic SAMs on silicon wafers. Electron-beam lithography of a thin poly(methyl methacrylate) (PMMA) resist layer was used to define trenches, and (3-aminopropyl)triethoxysilane (APTES), a cationic SAM precursor, was deposited from aqueous solution onto the exposed silicon dioxide at the trench bottoms. The remaining PMMA can be cleanly stripped off with dichloromethane, leaving APTES layers 0.7-1.2 nm in thickness and 110 nm in width. DNA rafts bind selectively to the resulting APTES stripes. The coverage of DNA rafts on adjacent areas of silicon dioxide is 20 times lower than on the APTES stripes. The topographic features of the rafts, measured by AFM, are identical to those of rafts deposited on wide-area SAMs. Binding to the APTES stripes appears to be very strong as indicated by "jamming" of the rafts at a saturation coverage of 42% and the stability to repeated AFM scanning in air.

We demonstrate immobilization of DNA nanostructures (37 nm x 8 nm) on silicon by a combination of "top-down" fabrication and "bottom-up" self-assembly. Anchor lines and pads were defined using electron beam lithography and a cationic molecular monolayer. Individual DNA nanostructures bind in 85% yield onto the anchor pads and can be washed and imaged in air. The strength of the binding interaction between a DNA nanostructure and its anchor pad is at least -43 kJ/mol.

Abstract-Electron beam lithography (EBL) patterning of poly(methylmethacrylate) (PMMA) is a versatile tool for defining molecular structures on the sub-10-nm scale. We demonstrate lithographic resolution to about 5 nm using a cold-development technique. Liftoff of sub-10-nm Au nanoparticles and metal lines proves that cold development completely clears the PMMA residue on the exposed areas. Molecular liftoff is performed to pattern DNA rafts with high fidelity at linewidths of about 100 nm. High-resolution EBL and molecular liftoff can be applied to pattern Creutz-Taube molecules on the scale of a few nanometers for quantum-dot cellular automata.

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