Electron Beam Induced Deposition Process Research Articles

Superconducting single-photon detectors fabricated via a focused electron beam-induced deposition process

Superconducting detectors have become essential devices for high-performance single-photon counting over a wide wavelength range with excellent time resolution. Detector fabrication typically relies on resist-based lithography processes, which can limit possibilities for device integration, e.g., on unconventional substrates. Here, we demonstrate a resist-free fabrication route for realizing superconducting nanowire single-photon detectors based on focused electron beam-induced deposition. Utilizing direct writing of a Pt–C mask, we achieved nanowire meanders with linewidths below 100 nm, operated them as superconducting devices for the detection of visible and near-infrared photons, and showed detector integration on side-polished optical fibers. Being compatible with device fabrication on curved irregular surfaces, our approach could enable superconducting detector integration in complex configurations.

Multiscale simulation of the focused electron beam induced deposition process

Focused electron beam induced deposition (FEBID) is a powerful technique for 3D-printing of complex nanodevices. However, for resolutions below 10 nm, it struggles to control size, morphology and composition of the structures, due to a lack of molecular-level understanding of the underlying irradiation-driven chemistry (IDC). Computational modeling is a tool to comprehend and further optimize FEBID-related technologies. Here we utilize a novel multiscale methodology which couples Monte Carlo simulations for radiation transport with irradiation-driven molecular dynamics for simulating IDC with atomistic resolution. Through an in depth analysis of hbox {W(CO)}_6 deposition on hbox {SiO}_2 and its subsequent irradiation with electrons, we provide a comprehensive description of the FEBID process and its intrinsic operation. Our analysis reveals that simulations deliver unprecedented results in modeling the FEBID process, demonstrating an excellent agreement with available experimental data of the simulated nanomaterial composition, microstructure and growth rate as a function of the primary beam parameters. The generality of the methodology provides a powerful tool to study versatile problems where IDC and multiscale phenomena play an essential role.

Formation mechanisms of boron oxide films fabricated by large-area electron beam-induced deposition of trimethyl borate.

Boron-containing materials are increasingly drawing interest for the use in electronics, optics, laser targets, neutron absorbers, and high-temperature and chemically resistant ceramics. In this article, the first investigation into the deposition of boron-based material via electron beam-induced deposition (EBID) is reported. Thin films were deposited using a novel, large-area EBID system that is shown to deposit material at rates comparable to conventional techniques such as laser-induced chemical vapor deposition. The deposition rate and stoichiometry of boron oxide fabricated by EBID using trimethyl borate (TMB) as precursor is found to be critically dependent on the substrate temperature. By comparing the deposition mechanisms of TMB to the conventional, alkoxide-based precursor tetraethyl orthosilicate it is revealed that ligand chemistry does not precisely predict the pathways leading to deposition of material via EBID. The results demonstrate the first boron-containing material deposited by the EBID process and the potential for EBID as a scalable fabrication technique that could have a transformative effect on the athermal deposition of materials.

Oxygen-assisted purification of platinum structures deposited by ion and electron beam induced processes

Purification in the presence of O2 flux is investigated in platinum structures grown by ion and electron beam induced deposition processes using a standard precursor, MeCpPtMe3. Two different room temperature purification processes are evaluated. In the first process, the purification is obtained by simultaneously supplying oxygen and precursor gas during the deposition. In the second process, an in situ post-treatment is performed on deposited structures by electron irradiation in the presence of oxygen. The first process applied to electron beam deposition requires a high flux of oxygen to improve the purification efficiency, while application to ion beam deposition requires a lower oxygen flux to enhance purification while avoiding an additional increase of the milling process. Both purification processes result in high purity Pt depositions and a reduction of deposition yields. For the ion beam, the electrical resistivity only drops for the first purification process: deposition supplying simultaneously oxygen and gas precursor. The second process of electron post irradiation does result in compositional changes, including reduced amounts of carbon but does not result in improvements in resistivity. For the electron beam, the resistivity shows a significant reduction applying both purification processes in sequence: in this way a resistivity of 22.5 µΩ cm has been obtained which is only twice the bulk value for Pt.

XPS study of thermal and electron-induced decomposition of Ni and Co acetylacetonate thin films for metal deposition

Optimizing thin metal film deposition techniques from metal-organic precursors such as atomic layer deposition, chemical vapor deposition (CVD), or electron beam-induced deposition (EBID) with the help of surface science analysis tools in ultrahigh vacuum requires a contamination-free precursor delivery technique, especially in the case of the less volatile precursors. For this purpose, the preparation of layers of undecomposed Ni(acac)2 and Co(acac)2 was tried via pulsed spray evaporation of a liquid solution of the precursors in ethanol into a flow of nitrogen on a CVD reactor. Solvent-free layers of intact precursor molecules were obtained when the substrate was held at a temperature of 115 °C. A qualitative comparison of thermally initiated and electron-induced precursor decomposition and metal center reduction was carried out. All deposited films were analyzed with respect to chemical composition quasi in situ by x-ray photoelectron spectroscopy. Thermally initiated decomposition yielded higher metal-to-metal oxide ratios in the deposit than the electron-induced process for which ratios of 60:40 and 20:80 were achieved for Ni and Co, resp. Compared to continuous EBID processes, all deposits showed low levels of carbon impurities of ∼10 at. %. Therefore, postdeposition irradiation of metal acetylacetonate layers by a focused electron beam and subsequent removal of intact precursor by dissolution in ethanol or by heating is proposed as electron beam lithography technique on the laboratory scale for the production of the metal nanostructures.

Characterization of Nanoporous Materials with Atom Probe Tomography.

A method to characterize open-cell nanoporous materials with atom probe tomography (APT) has been developed. For this, open-cell nanoporous gold with pore diameters of around 50 nm was used as a model system, and filled by electron beam-induced deposition (EBID) to obtain a compact material. Two different EBID precursors were successfully tested-dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9]. Penetration and filling depth are sufficient for focused ion beam-based APT sample preparation. With this approach, stable APT analysis of the nanoporous material can be performed. Reconstruction reveals the composition of the deposited precursor and the nanoporous material, as well as chemical information of the interfaces between them. Thus, it is shown that, using an appropriate EBID process, local chemical information in three dimensions with sub-nanometer resolution can be obtained from nanoporous materials using APT.

Electron Beam Induced Reactions of Adsorbed Cobalt Tricarbonyl Nitrosyl (Co(CO)3NO) Molecules

This study focuses on elucidating the bond breaking steps involved in the electron beam induced deposition (EBID) of nanostructures created from the organometallic precursor cobalt tricarbonyl nitrosyl (Co(CO)3NO) by studying the effect of 500 eV incident electrons on nanometer scale films of Co(CO)3NO. Experiments were performed under ultrahigh vacuum conditions, using a suite of surface analytical techniques, principally X-ray photoelectron spectroscopy and mass spectrometry. The purely electron stimulated reactions of Co(CO)3NO adsorbed on gold or amorphous carbon substrates at low temperatures (−168 °C) occurs in two distinct steps. The first step involves a one electron process that initiates decomposition of the nitrosyl (NO) ligand to form a nitride, accompanied by the simultaneous desorption of at least one CO ligand to create a partially decarbonylated intermediate. This first step decomposes Co(CO)3NO into a nonvolatile Co-containing compound and therefore initiates the EBID process. In the seco...

Optimization of electron beam induced deposition process for the fabrication of diode-like Pt/SiO2/W devices

Pt/SiO2/W devices of controlled size, thickness, and interfaces were fabricated by electron beam induced deposition (EBID) in a focused ion beam (FIB) system, for possible applications as metal-insulator-metal diodes. A systematic study of the deposition parameters used for the fabrication of the devices was carried out by scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy (TEM). In particular, the morphological and structural quality of the deposited layers, their mutual interfaces, and the thickness of the insulating layer were accurately investigated, being key issues for the application of these multilayer structures as tunneling diodes; to this aim, a novel TEM sample preparation approach was developed, which allows the in situ FIB preparation of ready-to-be-observed multilayer structures; by using this approach, TEM samples can be directly made, by depositing the structures in the same conditions used for the device fabrication, in the correct geometry for the cross sectional investigations and, without any further preparation steps. The capability of the EBID technique to fabricate submicrometer electronic devices with promising electrical properties, such as asymmetry and nonlinearity, was demonstrated.

A new sequential EBID process for the creation of pure Pt structures from MeCpPtMe3

Electron beam induced deposition (EBID) is a process used for the fabrication of three-dimensional nanostructures of a variety of materials, but direct deposition of pure metallic structures has rarely been achieved. Typically, MeCpPtMe3 as a precursor for Pt leads to a carbon rich deposit with ∼15 at.% Pt, which negatively affects its application as an electrical contact. We report a new process for Pt purification: in situ annealing with electron beam post-irradiation under oxygen flux, which can completely purify a thin (<100 nm) Pt EBID structure at substrate temperatures as low as 120 °C. We have developed a sequential method in which a thin Pt EBID structure is deposited on a previously purified structure and subsequently purified. The resistivity of the contact grown by this sequential procedure is observed to be ∼70 ± 8 μΩ cm—only six times higher than that of pure bulk Pt. Thus, sequential deposition and purification proves to be an effective method for fabricating pure Pt structures of desired dimensions.

Enhanced material purity and resolution via synchronized laser assisted electron beam induced deposition of platinum

We introduce a laser assisted electron beam induced deposition (LAEBID) process which is a nanoscale direct write synthesis method that integrates an electron beam induced deposition process with a synchronized pulsed laser step to induce thermal desorption of reaction by-products. Localized, spatially overlapping electron and photon pulses enable the thermal desorption of the reaction by-product while mitigating issues associated with bulk substrate heating, which can shorten the precursor residence time and distort pattern fidelity due to thermal drift. Current results demonstrate purification of platinum deposits (reduced carbon content by ~50%) with the addition of synchronized laser pulses as well as a significant reduction in deposit resistivity. Measured resistivities from platinum LAEBID structures (4 × 10(3)μΩ cm) are nearly 4 orders of magnitude lower than standard EBID platinum structures (2.2 × 10(7)μΩ cm) from the same precursor and are lower than the lowest reported EBID platinum resistivity with post-deposition annealing (1.4 × 10(4)μΩ cm). Finally the LAEBID process demonstrates improved deposit resolution by ~25% compared to EBID structures under the conditions investigated in this work.

Fabrication of an UltraLow-Resistance Ohmic Contact to MWCNT–Metal Interconnect Using Graphitic Carbon by Electron Beam-Induced Deposition (EBID)

Reduction in contact resistance is one of the foremost challenges for carbon nanotube/graphene nanodevices. In this study, we present a novel fabrication process for low-temperature, Ohmic contact between open-ended multiwalled carbon nanotubes (MWCNTs) and metal interconnects using graphitic carbon deposited via electron beam-induced deposition (EBID). The electrical and structural properties of the contact interface are characterized for making connection to the single (outermost) shell only, as well as to multiple conducting shells of MWCNTs. In addition to establishing the scaling relationship between the carbon contact length and the resulting contact resistance, the magnitude of the contact resistance has been quantified with and without post-deposition thermal annealing. The results indicate that the contact is Ohmic in nature, and ranges from 26.5 kΩ for the connection made to the outermost shell of an MWCNT down to just 116 Ω for the multiple-shell connection performed via a process suggested through the EBID process simulations. These results provide a significant advance in application of MWCNTs to future interconnect technologies.

Fabrication of pure gold nanostructures by electron beam induced deposition with Au(CO)Cl precursor: deposition characteristics and primary beam scattering effects

In the search for a direct write, high-purity electron beam induced deposition (EBID) process, a new gold precursor that is commonly available is investigated. This precursor, Au(CO)Cl, can indeed be used to produce a high-purity golden nanostructure (>95 at% Au), at a wide variety of electron beam parameters. The use of a mass spectrometer to determine the components of the actual precursor vapour showed that the Au(CO)Cl density in the vapour is very low (estimated at <0.1%), while the main component is CO. This indicates that the electron decomposition cross-section of the actual precursor is roughly two orders of magnitude higher than for common EBID precursors. A remarkable observation is a skirt deposition at positions between 5 and 200 µm away from the beam impact point. This skirt cannot be attributed to secondary electrons of type II (SE2), but results from local scattering of the primary beam on its way through the precursor gas. The skirt deposition is quantified experimentally and by modelling and must be present in all EBID processes with any precursor, delivered through a local supply system with fluxes in the range 1016–1019 molecules cm−2 s−1. It is shown that the skirt effect can be minimized by increasing the applied beam energy and by reducing the gas path length.

Low resistivity Pt interconnects developed by electron beam assisted deposition using novel gas injector system

Electron beam-induced deposition (EBID) is a direct write process where an electron beam locally decomposes a precursor gas leaving behind non-volatile deposits. It is a fast and relatively in-expensive method designed to develop conductive (metal) or isolating (oxide) nanostructures. Unfortunately the EBID process results in deposition of metal nanostructures with relatively high resistivity because the gas precursors employed are hydrocarbon based. We have developed deposition protocols using novel gas-injector system (GIS) with a carbon free Pt precursor. Interconnect type structures were deposited on preformed metal architectures. The obtained structures were analysed by cross-sectional TEM and their electrical properties were analysed ex-situ using four point probe electrical tests. The results suggest that both the structural and electrical characteristics differ significantly from those of Pt interconnects deposited by conventional hydrocarbon based precursors, and show great promise for the development of low resistivity electrical contacts.

Fundamental Proximity Effects in Focused Electron Beam Induced Deposition

Fundamental proximity effects for electron beam induced deposition processes on nonflat surfaces were studied experimentally and via simulation. Two specific effects were elucidated and exploited to considerably increase the volumetric growth rate of this nanoscale direct write method: (1) increasing the scanning electron pitch to the scale of the lateral electron straggle increased the volumetric growth rate by 250% by enhancing the effective forward scattered, backscattered, and secondary electron coefficients as well as by strong recollection effects of adjacent features; and (2) strategic patterning sequences are introduced to reduce precursor depletion effects which increase volumetric growth rates by more than 90%, demonstrating the strong influence of patterning parameters on the final performance of this powerful direct write technique.

Interaction of W(CO)6with SiO2surfaces: A density functional study

The interaction of tungsten hexacarbonyl W(CO)$_6$ precursor molecules with SiO$_2$ substrates is investigated by means of density functional theory calculations with and without inclusion of long range van der Waals interactions. We consider two different surface models, a fully hydroxylated and a partially hydroxylated SiO$_2$ surface, corresponding to substrates under different experimental conditions. For the fully hydroxylated surface we observe only a weak interaction between the precursor molecule and the substrate with physisorption of W(CO)$_6$. Inclusion of van der Waals corrections results in a stabilization of the molecules on this surface, but does not lead to significant changes in the chemical bonding. In contrast, we find a spontaneous dissociation of the precursor molecule on the partially hydroxylated SiO$_2$ surface where chemisorption of a W(CO)$_5$ fragment is observed upon removal of one of the CO ligands from the precursor molecule. Irrespective of the hydroxylation, the precursor molecule prefers binding of more than one of its CO ligands. In the light of these results, implications for the initial growth stage of tungsten nano-deposits on SiO$_2$ in an electron beam induced deposition process are discussed.

Tuning electromechanical response of individual CNT by selective electron beam induced deposition

Carbon nanotubes have been recognized as one of the most promising materials for developing nanoelectromechanical systems. In particular, the electron beam induced deposition (EBID) process of amorphous carbon under scanning electron microscopy (SEM) represents a very well known and suitable technique for the realization of a stable mechanical and electrical contact between CNTs and the supporting material. Within this context, the effect of the EBID process on the electromechanical response of an individual multiwalled CNT was directly investigated by using a piezoelectric nanomanipulation system operating inside an SEM chamber. The experimental system ensures a high control capability on the geometric parameters of the as fabricated cantilevered CNT based structure, thus allowing a precise modelization of the electrostatic CNT deflection process. The amorphous carbon coating was found to produce a variation of the mechanical response of the CNT cantilevered system, suggesting the use of EBID under SEM as an effective method for tuning the electromechanical properties of single CNT based nanostructures.

Electron beam induced deposition of residual hydrocarbons in the presence of a multiwall carbon nanotube

Amorphous carbon deposited via electron beam induced deposition (EBID) is frequently used to make a low-temperature Ohmic contact with low electrical resistance and improved mechanical characteristics of the multiwall nanotube (MWNT) substrate or MWNT-MWNT interface. However, influence of the MWNT on the EBID process has not been quantified. In this work, we experimentally and theoretically investigate the growth dynamics of EBID of residual hydrocarbons in presence of a MWNT. We demonstrate that the properties of MWNT do not impact amorphous carbon deposition process.

Electron-Beam-Induced Deposition of Platinum from a Liquid Precursor

We demonstrate here the first focused electron-beam-induced deposition (EBID) of nanostructures using a liquid precursor. We have deposited sub-50 nm platinum (Pt) wires and dots from a dilute, aqueous solution of chloroplatinic acid. Existing EBID processes rely on the electron-beam stimulated decomposition of gaseous precursors; as a result, the deposits are highly contaminated (up to 75 at. % carbon or 60 at. % phosphorus for Pt processes). In contrast, we show that deposition of platinum by electron-beam reduction of platinum ions from solution leads to high-purity deposits (approximately 10 at. % chlorine contamination) at rates at least ten times higher than those obtained with other platinum precursors. Liquid-phase EBID offers a new route to deterministic, three-dimensional, nanometer-scale structures composed of multiple materials without complex multistep processing. Thus, it may prove important for prototyping and low-volume production of nanoscale devices and for repair and modification of nanoscale masks and templates used in high-volume production.

The influence of beam defocus on volume growth rates for electron beam induced platinumdeposition

Electron beam induced deposition (EBID) is a versatile method for the controlledfabrication of conducting, semi-conducting and non-conducting structures down to thenanometer scale. In contrast to ion beam induced deposition, EBID processes are free ofsputter effects, ion implantation and massive heat generation; however, they havemuch lower deposition rates. To push the deposition efficiency further towards itsintrinsic limits, the individual influences of the process parameters have to beexplored. In this work a platinum pre-cursor is used for the deposition of conductingnanorods on highly oriented pyrolytic graphite. The study shows the influence ofa beam defocus during deposition on the volume growth rates. The temporalevolution of volume growth rates reveals a distinct maximum which is dependent onthe defocus introduced, leading to an increase of deposited volumes by a factor2.5 after the same deposition times. The observed maximum is explained by anincreasing and saturating electron yield contributing to the final deposition processand constantly decreasing diffusion abilities of the pre-cursor molecules towardthe tip of the nanorods, which is further supported by dwell time experiments.

Single-crystal nanowires grown via electron-beam-induced deposition

Electron-beam-induced deposition (EBID) is a useful technique for direct-writing ofthree-dimensional dielectric, semiconductor, and metallic materials with nanoscaleprecision and resolution. The EBID process, however, has been limited in manycases because precursor byproducts (typically from organic precursors likeW(CO)6) are incorporated into the deposited material resulting in contaminated and amorphousstructures. In this work, we have investigated the structure and composition ofEBID tungsten nanostructures as-deposited from a tungsten hexafluoride(WF6) precursor. High resolution transmission electron microscopy, electron diffractionand electron spectroscopy were employed to determine the effects that theelectron beam scanning conditions have on the deposit characteristics. Theresults show that slow, one-dimensional lateral scanning produces texturedβ-tungsten nanowire cores surrounded by an oxide secondary layer,while stationary vertical growth leads to single-crystal [100]-orientedW3O nanowires. Furthermore we correlate how the growth kinetics affect the resultant nanowirestructure and composition.