Neon Focussed-Ion-Beam Nanofabrication

Our vision is to create a state-of-the-art three-dimensional nanofabrication facility for development of electron, photonic and nanofluidic devices, based on the neon focussed-ion-beam (FIB) instrument. It will transform the nanofabrication capabilities of the UK science and engineering community by offering rapid prototyping of devices with feature sizes below 10 nm. By using neon as the primary ion species, sampling poisoning effects will be radically reduced by comparison with conventional gallium-ion FIB. Neon beams also permit high-quality nanoscale machining of silicon, which is not possible with the recently-introduced helium-ion FIB. Furthermore sputtering rates (which ultimate limit throughput) are an order of magnitude higher than with helium ions, allowing significant volumes of material to be machined within laboratory timescales.

Over the last twenty years, FIB has become a dominant nanofabrication tool for research labs. It is particularly well suited to the research environment since prototype devices can very quickly be created without the need for extensive process development. The Achilles heel of commercial FIB systems, however, is that (until recently) they all use gallium ions. The reactivity and high mobility of these gallium ions once they have been (unavoidably) implanted into a nanofabricated sample often leads to deleterious sample poisoning effects. For example, the properties of correlated electron systems in functional oxides intimately depend upon the oxygen stoichiometry and order; in most oxides these are irreversibly perturbed by Ga ions. Similarly the optical losses in plasmonic nano-apertures are limited by the damage done to the Ga-ion-milled dielectric. Furthermore, the electrical properties of nanoelectronic devices are also directly affected by Ga implantation.

Recognising these limitations, Carl Zeiss released a new FIB microscope five years ago in which the Ga source is replaced by a helium gas field-ion source (GFIS). The main advantage over Ga is that the ion species is now an inert gas, thereby removing the sample poisoning problem at a stroke. The helium GFIS FIB microscope is therefore a rival to the field-emission scanning electron microscope for imaging applications. The obvious disadvantage of using helium, however, is that the sputter yield (i.e. the rate at which material is removed by incident ions) is typically 30 times smaller for He ions than for Ga ions. This greatly increases the fabrication time, rendering He ions unsuitable for many applications.

This naturally suggests the use of heavier inert gases in the GFIS, an opportunity which Carl Zeiss are now realising with its new neon GFIS FIB system. (This product is scheduled to be released in September 2012.) The sputter yield for neon ions is typically ten times greater than that for He ions. For nanofabrication applications the use of neon represents an ideal combination of rapid fabrication and minimal poisoning. Demonstrations of neon-ion nanofabrication at Carl Zeiss's development laboratory show machined resolution better than 10 nm. This rivals that obtainable with state of the art electron-beam lithography, with the added advantages of rapid prototyping and the possibility (since FIB is a resist-less technique, allowing the beam to be aligned at an arbitrary angle with respect to the sample surface) of three-dimensional nanopatterning.

Nanotechnology can be thought of as a "toolbox" which can be used to make an impact in all of EPSRC's global, economic and societal challenge themes. The neon FIB, since it is a prototyping nanofabrication instrument, will make a central contribution to addressing these challenge themes. Since sample poisoning is minimal, the scaling up of prototype fabrication processes to future (non-FIB) manufacturing techniques will be much more straightforward than with gallium FIB. We can therefore expect neon FIB to make significant contributions within a ten-year timescale to:

(a) Manufacturing the Future, for example by creating nanoelectronic devices based on new materials with reduced environmental footprints;
(b) Energy, for example by creating nanoplasmonic devices for solar energy concentrators;
(c) The Digital Economy, for example by enabling high density low power spintronics devices using functional oxide materials;
(d) Healthcare Technologies, for example by fabrication of new nanofluidic devices for point-of-care DNA sequencing and other analytical technologies.

FIB has always been an important industrial tool in the electronics sector for correcting fabrication errors both in lithographic masks and on integrated circuits themselves. Transistor dimensions are now, however, too small to be repaired by gallium FIB; so development of neon FIB techniques for these circuit edit applications would make a big impact on the UK and European electronics sector within a three-year timescale. In the longer term we can expect new prototype devices (for example point-of-care diagnostic tools based on nanopores fabricated using neon FIB) to have an impact in the medical sector.