High resolution resist-free lithography in the SEM

Focussed Electron Beam Induced Processing is a high resolution direct-write nanopatterning technique. Its ability to fabricate sub-10 nm structures together with its versatility and ease of use, in that it is resist-free and implementable inside a Scanning Electron Microscope, make it attractive for a variety of applications in nanofabrication. FEBIP comprises two complementary techniques: Electron Beam Induced Deposition and Electron Beam Induced Etching. In EBID (EBIE), the electron beam is scanned in the presence of a precursor gas that has been let into the chamber of the SEM. The precursor molecules adsorbed onto the sample surface are dissociated by the electron beam, as well as by secondary and backscattered electrons that are generated at the surface by the interaction of the electron beam with the sample. The nonvolatile dissociation product forms a deposit (etch) on the surface, while the volatile products are pumped out. A pattern can thus be deposited (etched) by merely scanning the beam in the presence of the precursor. As the secondary electrons are lower in energy (< 50 eV), they contribute more significantly to the dissociation than the higher energy backscattered or primary electrons. At the outset therefore, the resolution in EBID is limited by the emission radius of the secondary electrons, which can be as low as a few nanometres. The fabrication of lines as little as 3 nm wide on bulk silicon attests to the high resolution patterning capability of EBID, which in turn makes it potentially attractive for lithography. The development of a laboratory nanofabrication technique into a viable alternative for lithography, however, requires several criteria to be met.