Direct fabrication of nanowires in an electron microscope

Abstract

Electron-beam-induced deposition ͑EBID͒ is a potentially fast and resistless deposition technique which might overcome the fundamental resolution limits of conventional electron-beam lithography. We advance the understanding of the EBID process by simulating the structure growth. The merit of our model is that it explains the shapes of structures grown by EBID quantitatively. It also predicts the possibility to directly fabricate structures with lateral sizes smaller than 10 nm and points out the ideal conditions to achieve this goal. We verify these predictions by fabricating sub-10-nm lines and dots in a state-of-the-art scanning transmission electron microscope. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1575506͔ Energetic beams of photons, ions, and electrons are currently in use for fabrication of submicron devices for such diverse applications as microelectronics, nanophysics, and molecular biology. Among these, the focused electron beam fabricates the smallest features. The conventional electronbeam-induced lithography, based on polymethylmethacrylate resist has reached its fundamental resolution limits, situated around 10 nm, as dictated by the interaction range of electrons with the resist, by the molecular size, and by the resist development mechanism. To fabricate even smaller structures, we investigate a resistless technique, called electronbeam-induced deposition ͑EBID͒, which might overcome the present resolution limitation problem.Originally EBID was well known as contamination growth in electron microscopy. Broers et al.1 were the first to use contamination grown patterns as an etching mask to define 8-nm-wide metal lines. Only in the last decade has EBID gained more importance as a tool for additive lithography, 2 practiced mainly in scanning electron microscopes ͑SEM͒. The principle of EBID is illustrated in Fig. 1 and can be described briefly as follows. In a high vacuum chamber, an electron beam is focused on a substrate surface on which precursor gas molecules, containing the element to be deposited ͑organometallic compound or hydrocarbon͒, are adsorbed. As a result of complex beam-induced surface reactions, the precursor molecules adsorbed in and near to the irradiated area, dissociate into nonvolatile ͑the deposit͒ and volatile fragments ͑to be pumped away͒. The advantage of EBID over conventional lithography methods is that two-, and even three-dimensional ͑3D͒, 2-4 structures are patterned and deposited simultaneously, making it a fast, one-step technique.The theoretical understanding of EBID is rather poor. Until now, there has not been a proper explanation for the fact that the smallest structures fabricated with EBID are typically 15-20-nm wide, even though electron optical instruments, like SEMs and scanning transmission electron microscopes ͑STEMs͒, with much smaller probe sizes were used. [5][6][7][8] We improve the understanding by modeling the material growth under electron-beam irradiation. The merit of our model is not only that it explains the shapes of structures g...

Electron flux controlled switching between electron beam induced etching and deposition

“…Figures 3͑a͒ and 3͑b͒ show carbonaceous deposits 34 produced in a high vacuum environment ͑i.e., in the absence of an etch precursor͒ using a stationary electron beam and beam currents of ͑a͒ 71 and ͑b͒ 245 pA. Each deposit consists of a pillar at the beam impact point, surrounded by a ring 35 with a diameter corresponding to the backscattered electron 36,37 ͑BSE͒ escape area. The pillars are produced by primary beam electrons and, to a greater extent, 28,38 by the so-called "type 1" SEs ͑Refs. 36 and 37͒ excited by the primaries.…”

Substrate temperature and electron fluence effects on metallic films created by electron beam induced deposition

“…[1][2][3][4] To create metal containing EBID materials, deposition is accomplished by irradiating a surface with a focused electron beam in a constant partial pressure of a sufficiently volatile precursor, typically in an electron microscope. Deposition occurs when transiently adsorbed precursors undergo electron stimulated decomposition and form nonvolatile products.…”

“…8 For example, using the Me 2 Au(tfac) precursor Koops et al showed that depositions carried out at a substrate temperature of 80 C resulted in EBID materials with lower resistivity compared to deposits created on substrates maintained at room temperature. 13 The lower resistivity was ascribed to the fact that the atomic percentage of Au in the deposits increased significantly when the substrate temperature during deposition was increased (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) at. % at room temperature vs 70 at.…”

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Using three different precursors [MeCpPtMe 3 , Pt(PF 3 ) 4 , and W(CO) 6 ], an ultra-high vacuum surface science approach has been used to identify and rationalize the effects of substrate temperature and electron fluence on the chemical composition and bonding in films created by electron beam induced deposition (EBID). X-ray photoelectron spectroscopy data indicate that the influence of these two processing variables on film properties is determined by the decomposition mechanism of the precursor.

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Nanofabrication by advanced electron microscopy using intense and focused beam∗

“…The curves of the dissociation cross section as a function of electron energy are known for simple gases [39], but such curves for gases used in EBID are limited [40][41][42]. Curves for EBID gases generally have a peak at a low energy of approximately 100 eV and the secondary-electron distribution has been studied using a Monte Carlo method proposed by Silvis-Cividjian and coworkers [43,44]. Figure 12 shows a schematic illustration of the display window of our Monte Carlo simulation [45] during calculation.…”