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.

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...

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Recently, the fabrication resolution in electron beam-induced deposition (EBID) has improved significantly. Dots with an average diameter of 1 nm have been made. These results were all obtained in transmission electron microscopes on thin samples. As one may think that such resolution can be achieved on thin samples only, it is the objective of this paper to show that this should also be possible on thick samples. For that purpose we use Monte Carlo simulations of the electron-sample interaction and determine the surface area where secondary electrons are emitted. Assuming that these electrons cause the deposition in EBID, a comparison can be made between deposition on a thin and a thick sample. The Monte Carlo code we developed will be described and applied to the deposition induced by a 200 keV primary electron beam on an ultra-thin (10 nm) and a bulk-like (1,000 nm) Cu sample. Near the point of incidence of the primary beam, the deposit size is independent of the substrate thickness, such that a 1-nm resolution should be possible to achieve on a thick substrate as well. Thicker substrates only affect the tails of the deposit distribution which contain more mass than thin substrate deposit tails.