Ice Lithography for Nanodevices

Abstract

We report the successful application of a new approach, ice lithography (IL), to fabricate nanoscale devices. The entire IL process takes place inside a modified scanning electron microscope (SEM), where a vapor-deposited film of water ice serves as a resist for e-beam lithography, greatly simplifying and streamlining device fabrication. We show that labile nanostructures such as carbon nanotubes can be safely imaged in an SEM when coated in ice. The ice film is patterned at high e-beam intensity and serves as a mask for lift-off without the device degradation and contamination associated with e-beam imaging and polymer resist residues. We demonstrate the IL preparation of carbon nanotubes field effect transistors (FETs) with high quality trans-conductance properties.

Ice-assisted electron beam lithography of graphene

“…Ice lithography requires ~10 3 larger electron doses than conventional e-beam lithography [22, 23]. One may anticipate graphene damage induced by backscattered electrons returning to the surface from the bulk many microns from where the incident e-beam enters the surface.…”

An ice lithography instrument

“…As previously shown, the ice overlaying carbon nanotubes shields the tubes from ebeam induced contamination or damage but does not impede their visualization. 2 Ice is removed from desired contacting electrode regions using a SEM lithography system (NPGS 9, Nabity, Bozeman, MT) and a beam blanker (Deben, Suffolk, UK). After ice removal, a SEM image can be taken to evaluate the quality of the writing, and the sample is then transferred into the metal deposition chamber.…”

“…The SEM cold finger cooled down from room temperature to 83 K in 30 min, and the cold finger dewar contained sufficient LN 2 for more than 8 h of care-free operation. The JEOL diffusion pump baffle contained sufficient LN 2 more than 12 h of operation. With the partial pressure of water in the SEM chamber below 10 −6 Pa, less than 20 monolayers of water molecules will grow on an exposed surface at <130 K in 30 min.…”

“…1,2 Although e-beam lithography using organic resists, such as poly(methylmethacrylate) (PMMA) serves as the backbone tool of many nanoscience laboratories, the process requires several time consuming steps carried out in different machines. More importantly, as demonstrated by electron transport studies of very clean as-grown single walled carbon nanotubes, 3,4 optimal device performance is frequently hampered by lift-off residues that contaminate the active nanoscale components.…”

“…Using ice lithography, we produced pristine single walled carbon nanotube field effect transistors with good electrical properties without any lift-off contamination. 2 Finally, high resolution, sub-20-nm-wide metal lines that normally require a high-end 100 kV e-beam lithography system can easily be patterned by ice lithography with a modest 30 kV e-beam lithography system.…”