Focused Electron Beam Induced Etching Research Articles

Sidewall angle tuning in focused electron beam-induced processing.

Structures fabricated using focused electron beam-induced deposition (FEBID) have sloped sidewalls because of the very nature of the deposition process. For applications this is highly undesirable, especially when neighboring structures are interconnected. A new technique combining FEBID and focused electron beam-induced etching (FEBIE) has been developed to fabricate structures with vertical sidewalls. The sidewalls of carbon FEBID structures have been modified by etching with water and it is shown, using transmission electron microscopy imaging, that the sidewall angle can be tuned from outward to inward by controlling the etch position on the sidewall. A surprising under-etching due to the emission of secondary electrons from the deposit was observed, which was not indicated by a simple model based on etching. An analytical model was developed to include continued etching once the deposit has been removed at the exposed pixel. At this stage the secondary electrons from the substrate then cause the adsorbed water molecules to become effective in etching the deposit from below, resulting in under-etched structures. The evolution of the sidewall angle during etching has also been experimentally observed in a scanning electron microscope by continuously monitoring the secondary electron detector signal.

Selected Area Manipulation of MoS2 via Focused Electron Beam-Induced Etching for Nanoscale Device Editing.

We demonstrate direct-write patterning of single and multilayer MoS2 via a focused electron beam-induced etching (FEBIE) process mediated with the XeF2 precursor. MoS2 etching is performed at various currents, areal doses, on different substrates, and characterized using scanning electron and atomic force microscopies as well as Raman and photoluminescence spectroscopies. Scanning transmission electron microscopy reveals a sub-40 nm etching resolution and the progression of point defects and lateral etching of the consequent unsaturated bonds. The results confirm that the electron beam-induced etching process is minimally invasive to the underlying material in comparison to ion beam techniques, which damage the subsurface material. Single-layer MoS2 field-effect transistors are fabricated, and device characteristics are compared for channels that are edited via the selected area etching process. The source-drain current at constant gate and source-drain voltage scale linearly with the edited channel width. Moreover, the mobility of the narrowest channel width decreases, suggesting that backscattered and secondary electrons collaterally affect the periphery of the removed area. Focused electron beam doses on single-layer transistors below the etching threshold were also explored as a means to modify/thin the channel layer. The FEBIE exposures showed demonstrative effects via the transistor transfer characteristics, photoluminescence spectroscopy, and Raman spectroscopy. While strategies to minimize backscattered and secondary electron interactions outside of the scanned regions require further investigation, here, we show that FEBIE is a viable approach for selective nanoscale editing of MoS2 devices.

Combined Focused Electron Beam-Induced Deposition and Etching for the Patterning of Dense Lines without Interconnecting Material.

High resolution dense lines patterned by focused electron beam-induced deposition (FEBID) have been demonstrated to be promising for lithography. One of the challenges is the presence of interconnecting material, which is often carbonaceous, between the lines as a result of the Gaussian line profile. We demonstrate the use of focused electron beam-induced etching (FEBIE) as a scanning electron microscope (SEM)-based direct-write technique for the removal of this interconnecting material, which can be implemented without removing the sample from the SEM for post processing. Secondary electron (SE) imaging has been used to monitor the FEBIE process, and atomic force microscopy (AFM) measurements confirm the fabrication of well separated FEBID lines. We further demonstrate the application of this technique for removing interconnecting material in high resolution dense lines using backscattered electron (BSE) imaging to monitor the process.

Maskless Direct-Write Etching of Nanopit Arrays in Si Using Focused Electron Beam Induced Etching

We have used a focused electron beam and chlorine injection in order to etch nanopits on predefined positions of a Si sample. With other methods it is often difficult to get exactly positioned nanopits. With this maskless, resistless direct-write approach nanopits with a diameter below 100 nm has been fabricated. We will report on the optimum processing conditions and present different geometries fabricated wit this technique. Finally, application examples will be given.

Using an energized oxygen micro-jet for improved graphene etching by focused electron beam

We report on an improved Focused Electron Beam Induced Etching (FEBIE) process, which exploits heated oxygen delivery via a continuous supersonic micro-jet resulting in faster graphene patterning and better etch feature definition. Positioning a micro-jet in close proximity to a graphene surface with minimal jet spreading due to a continuous regime of gas flow at the exit of the 10 μm inner diameter capillary allows for focused exposure of the surface to reactive oxygen at high mass flux and impingement energy of a supersonic gas stream localized to a small etching area exposed to electron beam. These unique benefits of focused supersonic oxygen delivery to the surface enable a dramatic increase in the etch rate of graphene with no parasitic carbon “halo” deposition due to secondary electrons from backscattered electrons (BSE) in the area surrounding the etched regions. Increase of jet temperature via local nozzle heating provides means for enhancing kinetic energy of impinging oxygen molecules, which further speed up the etch, thus minimizing the beam exposure time and required electron dose, before parasitic carbon film deposition due to BSE mediated decomposition of adsorbed hydrocarbon contaminants has a measurable impact on quality of graphene etched features. Interplay of different physical mechanisms underlying an oxygen micro-jet assisted FEBIE process is discussed with support from experimental observations.

Chlorine based focused electron beam induced etching: A novel way to pattern germanium

Focused electron beam induced etching (FEBIE) with chlorine as etching agent has been used to geometrically shape and to electrically modify semiconductor nanodevices. Selected sections of monocrystalline nanowires were modified directly without the requirement for a photomask or a resist layer. FEBIE as a subtractive nanofabrication technology allows to locally etch active semiconductor devices made of Si or Ge. In this work, chlorine is used as the etchant gas to thin germanium channel structures fabricated by standard photolithography. For effective material removal a sufficiently high electron influence is essential to avoid the pitfalls of this method. Topography and conductivity of FEBIE-modified structures prior and after the etching process was studied by AFM and by electrical I–V characteristics. The presented work demonstrates the potential of Cl-based FEBIE for device prototyping and electrical trimming of future Ge-based nanodevices.

Local, direct-write, damage-free thinning of germanium nanowires

A crystallinity-retaining, implantation-free focused electron beam induced etching (FEBIE) process has been exploited to modify germanium nanowires. This technique shows a high selectivity to the metal contacts applied to the nanowires as well as to the substrate which did not exhibit significant etching. Raman-spectroscopic as well as electrical measurements have been performed on the FEBIE-modified nanowires. Experimental data obtained in this study suggest than unintentional stress is often applied to the nanowires by the defined electrical contacts. Electrical measurements indicate that the electronic properties of the as-grown Ge nanowires can be significantly altered already by a slight surface modification, resulting in an increased conductivity of more than two orders of magnitude.

Effects of electrons on the shape of nanopores prepared by focused electron beam inducedetching

The fabrication of nanometric pores with controlled size is important for applicationssuch as single molecule detection. We have recently suggested the use of focusedelectron beam induced etching (FEBIE) for the preparation of such nanopores insilicon nitride membranes. The use of a scanning probe microscope as the electronbeam source makes this technique comparably accessible, opening the way towidespread fabrication of nanopores. Since the shape of the nanopores is criticallyimportant for their performance, in this work we focus on its analysis and study thedependence of the nanopore shape on the electron beam acceleration voltage. We showthat the nanopore adopts a funnel-like shape, with a central pore penetratingthe entire membrane, surrounded by an extended shallow-etched region at thetop of the membrane. While the internal nanopore size was found to dependon the electron acceleration voltage, the nanopore edges extended beyond theprimary electron beam spot size due to long-range effects, such as radiolysis anddiffusion. Moreover, the size of the peripheral-etched region was found to be lessdependent on the acceleration voltage. We also found that chemical etching is therate-limiting step of the process and is only slightly dependent on the accelerationvoltage. Furthermore, due to the chemical etch process the chemical compositionof the nanopore rims was found to maintain the bulk membrane composition.

Nanofabrication of insulated scanning probes for electromechanical imaging in liquidsolutions

In this paper, the fabrication and electrical and electromechanical characterization of insulatedscanning probes have been demonstrated in liquid solutions. The silicon cantilevers weresequentially coated with chromium and silicon dioxide, and the silicon dioxide was selectivelyetched at the tip apex using focused-electron-beam-induced etching (FEBIE) withXeF2. The chromium layer acted not only as the conductive path from the tip, but also as anetch-resistant layer. This insulated scanning probe fabrication process is compatible withany commercial AFM tip and can be used to easily tailor the scanning probe tip propertiesbecause FEBIE does not require lithography. The suitability of the fabricated probes isdemonstrated by imaging of a standard topographical calibration grid as well aspiezoresponse force microscopy (PFM) and electrical measurements in ambient and liquidenvironments.

The controlled fabrication of nanopores by focused electron-beam-induced etching

The fabrication of nanometric holes within thin silicon-based membranes is of greatimportance for various nanotechnology applications. The preparation of such holes withaccurate control over their size and shape is, thus, gaining a lot of interest. In this work wedemonstrate the use of a focused electron-beam-induced etching (FEBIE) process as apromising tool for the fabrication of such nanopores in silicon nitride membranes and studythe process parameters. The reduction of silicon nitride by the electron beamfollowed by chemical etching of the residual elemental silicon results in a lineardependence of pore diameter on electron beam exposure time, enabling accurate controlof nanopore size in the range of 17–200 nm in diameter. An optimal pressure of5.3 × 10−6 Torr for the production of smaller pores with faster process rates, as a result of masstransport effects, was found. The pore formation process is also shown to be dependent onthe details of the pulsed process cycle, which control the rate of the pore extension, and itsminimal and maximal size. Our results suggest that the FEBIE process may play a key rolein the fabrication of nanopores for future devices both in sensing and nano-electronicsapplications.

Controlled focused electron beam-induced etching for the fabrication of sub-beam-size nanoholes

Sub-beam-size focused electron beam-induced etching of amorphous carbon membranes was achieved. The size of the tungsten filament generated electron beam was determined from the in situ stage current monitoring and verified by knife edge measurements. The in situ time resolved stage current measurements as an end point detection allowed the fabrication of nanoholes with a diameter of sub-20nm, corresponding to 20%–40% of the full width at half maximum of the incident beam.