High-vacuum versus ''environmental'' electron beam deposition (original) (raw)
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Electron beam deposition for nanofabrication: Insights from surface science
Surface Science, 2011
Electron beam induced deposition (EBID) is a direct-write lithographic technique that utilizes the dissociation of volatile precursors by a focused electron beam in a low vacuum environment to create nanostructures. Notable advantages of EBID over competing lithographic techniques are that it is a single step process that allows three-dimensional free-standing structures to be created, including features with single-nanometer scale dimensions. However, despite the inherent advantages of EBID, scientific and technological issues are impeding its development as an industrial nanofabrication tool. Perhaps the greatest single limitation of EBID is that metal-containing nanostructures deposited from organometallic precursors typically possess unacceptable levels of organic contamination which adversely affects the material's properties. In addition to the issue of purity, there is also a lack of understanding and quantitative information on the fundamental surface reactions and reaction cross-sections that are responsible for EBID. In this prospective, we describe how surface analytical techniques have begun to provide mechanistic and kinetic insights into the molecular level processes associated with EBID. This has been achieved by observing the effect of electron irradiation on nanometer thick films of organometallic precursors adsorbed onto solid substrates at low temperatures (b 200 K) under ultra-high vacuum conditions. Experimental observations include probing changes in surface composition, metal oxidation state, and the evolution of volatile species. Insights into surface reactions associated with purification strategies are also detailed. We also discuss unresolved scientific challenges and opportunities for future EBID research.
Factors in Electrochemical Nanostructure Fabrication Using Electron-Beam Induced Carbon Masking
Journal of The Electrochemical Society, 2004
The present work investigates the fabrication of Au nanostructures using the masking effect of carbon patterns deposited by the electron-beam ͑E-beam͒ of a scanning electron microscope for electrochemical reactions. E-beam induced deposition is based on the decomposition of residual hydrocarbon species ͑molecules from the pump oil͒ to create a solid deposit at the point of impact of the E-beam. Subsequently, such E-beam deposited matter is used to completely block the electrochemical deposition of Au in the nanometer scale. In this work, several factors affecting the resolution of the process are studied. Electrochemical conditions as well as control of the E-beam C-deposit are investigated to optimize the lateral resolution of the process. Especially, it is demonstrated that the beam energy used for depositing the C-mask plays a crucial role in fabricating Au nanostructures in the sub-50 nm range.
Microelectronic Engineering, 2003
A new type of atomic force microscope is proposed for atomic force microscopic analysis inside a scanning electron microscope. We attached a piezoresisitive atomic force microscopic cantilever to a micro manipulator to achieve a compact and guidable setup, so that the tip can be positioned under observation of the scanning electron microscopy (SEM) system. Another manipulator and a glass drain tube serve as a precise local gas injection system for organometallic vapour. Electron beam induced deposition of tungstenhexacarbonyl is 25 carried out at a global chamber pressure of 2 ? 10 mbar or less. Characterization of the directly patterned tungsten carbide structures according to deposition rate and dotsize or linewidth is done by combination of atomic force microscopy and SEM analysis for different electron energies, exposure doses and stepsize of pattern generator. A deposition rate of 1550 nm /(nC / dot) and 10 900 nm /(nC / nm) for dot and line deposition, respectively, and a dotsize and linewidth in the range of 20 to 25 nm have been obtained.
Spatial resolution limits in electron-beam-induced deposition
Journal of Applied Physics, 2005
Electron-beam-induced deposition ͑EBID͒ is a versatile micro-and nanofabrication technique based on electron-induced dissociation of metal-carrying gas molecules adsorbed on a target. EBID has the advantage of direct deposition of three-dimensional structures on almost any target geometry. This technique has occasionally been used in focused electron-beam instruments, such as scanning electron microscopes, scanning transmission electron microscopes ͑STEM͒, or lithography machines. Experiments showed that the EBID spatial resolution, defined as the lateral size of a singular deposited dot or line, always exceeds the diameter of the electron beam. Until recently, no one has been able to fabricate EBID features smaller than 15-20 nm diameter, even if a 2-nm-diam electron-beam writer was used. Because of this, the prediction of EBID resolution is an intriguing problem. In this article, a procedure to theoretically estimate the EBID resolution for a given energetic electron beam, target, and gaseous precursor is described. This procedure offers the most complete approach to the EBID spatial resolution problem. An EBID model was developed based on electron interactions with the solid target and with the gaseous precursor. The spatial resolution of EBID can be influenced by many factors, of which two are quantified: the secondary electrons, suspected by almost all authors working in this field, and the delocalization of inelastic electron scattering, a poorly known effect. The results confirm the major influence played by the secondary electrons on the EBID resolution and show that the role of the delocalization of inelastic electron scattering is negligible. The model predicts that a 0.2-nm electron beam can deposit structures with minimum sizes between 0.2 and 2 nm, instead of the formerly assumed limit of 15-20 nm. The modeling results are compared with recent experimental results in which 1-nm W dots from a W͑CO͒ 6 precursor were written in a 200-kV STEM on a 30-nm SiN membrane.
Parallel electron-beam-induced deposition using a multi-beam scanning electron microscope
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2011
Lithography techniques based on electron-beam-induced processes are inherently slow compared to light lithography techniques. The authors demonstrate here that the throughput can be enhanced by a factor of 196 by using a scanning electron microscope equipped with a multibeam electron source. Using electron-beam induced deposition with MeCpPtMe 3 as a precursor gas, 14 Â 14 arrays of Pt-containing dots were deposited on a W/Si 3 N 4 /W membrane, with each array of 196 dots deposited in a single exposure. The authors demonstrate that by shifting the array of beams over distances of several times the beam pitch, one can deposit rows of closely spaced dots that, although originating from different beams within the array, are positioned within 5 nm of a straight line. V
Electron-beam-induced fabrication of metal-containing nanostructures
Scanning, 2006
An experimental system based on a transmission electron microscope JEM-100CX has been developed for electron beam-induced chemical vapor deposition. Direct electron beam-induced growth of nanometer-wide self-supporting rods has been performed inside the microscope operating in scanning mode by decomposition of carbonyls of chromium Cr(CO) 6 , tungsten W(CO) 6 , and rhenium Re 2 (CO) 10. In situ phase and structure transformations under annealing inside the microscope column were studied. Nanoscale rods and strips grown from rhenium carbonyl are of special interest because, after annealing, they consist of a single pure rhenium phase. The described method of metallic nanoelements fabrication enables us to produce highly conductive nanowires and tips for application in nanoelectronics, emission electronics, and scanning tunneling microscopy.
Constructing, connecting and soldering nanostructures by environmental electron beam deposition
Nanotechnology, 2004
Highly conductive nanoscale deposits with solid gold cores can be made by electron beam deposition in an environmental scanning electron microscope (ESEM), suggesting the method to be used for constructing, connecting and soldering nanostructures. This paper presents a feasibility study for such applications. We identify several issues related to contamination and unwanted deposition, relevant for deposition in both vacuum (EBD) and environmental conditions (EEBD). We study relations between scan rate, deposition rate, angle and line width for three-dimensional structures. Furthermore, we measure the conductivity of deposits containing gold cores, and find these structures to be highly conductive, approaching the conductivity of solid gold and capable of carrying high current densities. Finally, we study the use of the technique for soldering nanostructures such as carbon nanotubes. Based on the presented results we are able to estimate limits for the applicability of the method for the various applications, but also demonstrate that it is a versatile and powerful tool for nanotechnology within these limits.
Tip-based electron beam induced deposition using active cantilevers
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2019
Tip-based electron beam induced deposition is performed using field emission of low-energy electrons from the tip of an active (i.e., self-sensing and self-actuating) atomic force microscope cantilever inside a scanning electron microscope. By using the active cantilever for feature placement and metrology combined with fast switching between field-emission and noncontact imaging mode, high placement accuracy and time-efficient, precise 3D measurement of the deposits are enabled. First results on the effect of electron energy and exposure dose on the growth rates and dimensions of the deposits are presented, and the potential to increase spatial resolution due to the enhanced localization of the dissociation reactions induced by the low-energy electrons is discussed.
Electron-beam-induced deposition with carbon nanotube emitters
Applied Physics Letters, 2002
Electron-beam-induced deposition ͑EBID͒ is performed with multiwalled carbon nanotube emitters that are assembled to atomic force microscope cantilevers through nanorobotic manipulations. A typical experiment shows that under 120 V bias, field emission current 2 A occurs from a nanotube emitter. In comparison with conventional EBID with a Schottky-type electron gun of a field-emission scanning electron microscope ͑FESEM͒ in the same vacuum chamber, the deposition rate of the nanotube emitter reaches up to 12.2% of that of FESEM although the bias and the emission current are only 0.8% and 1.9% of those of FESEM ͑15 kV and 106 A͒. The concept of parallel EBID is also presented.