Focused electron beam-induced deposition at cryogenic temperatures
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M. Toth FEI Company, Hillsboro, Oregon 97124 (Received 12 July 2010; accepted 12 October 2010)
Direct-write, cryogenic electron beam-induced deposition (EBID) was performed by condensing methylcyclopentadienyl-platinum-trimethyl precursor onto a substrate at 155 °C, exposing the condensate by a 15 keV electron beam, and desorbing unexposed precursor molecules by heating the substrate to room temperature. Dependencies of film thickness, microstructure, and surface morphology on electron beam flux and fluence, and Monte Carlo simulations of electron interactions with the condensate are used to construct a model of cryogenic EBID that is contrasted to existing models of conventional, room temperature EBID. It is shown that material grown from a cryogenic condensate exhibits one of three distinct surface morphologies: a nanoporous mesh with a high surface-to-volume ratio; a smooth, continuous film analogous to material typically grown by room temperature EBID; or a film with a high degree of surface roughness, analogous to that of the cryogenic condensate. The surface morphology can be controlled reproducibly by the electron fluence used for exposure. I. INTRODUCTION 1–4
Electron beam-induced deposition (EBID) is a direct-write technique characterized by decomposition of surface adsorbed precursor molecules in the vicinity of an electron beam. EBID applications include circuit edit, lithographic mask repair, electrical contacts to nanometerscale structures, and rapid prototyping of integrated circuit and microelectromechanical system devices. In a recent review by Utke et al.,2 the impact of substrate temperature on EBID processes was identified as a topic of limited research. Several studies have investigated the effects of substrate heating, primarily for metal purity enhancement.5,6 Studies examining low-temperature substrates are scarce, and focus on growth rate enhancement.7,8 Of these studies on substrate temperature variation, structural properties of EBID deposits, and avenues for material manipulation have not been studied in detail. Low-temperature substrates in EBID enable multilayer adsorption of precursor, as opposed to mono- or submonolayer adsorption typically encountered in room temperature EBID. Cooling substrates to cryogenic temperatures has been shown to increase EBID growth rates for W7 and Sn8 films by as much as an order of magnitude. These improved growth rates are attributed to multilayer adsorption, which increases the probability of electronadsorbate interactions. Films grown by cryogenic EBID were described in some cases to be “discontinuous,” but the underlying growth mechanisms and the possibility of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.59 J. Mater. Res., Vol. 26, No. 3, Feb 14, 2011
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predictive tailoring deposit structure by growth parameters have not been investigated. Here, a common EBID precursor, methylcyclopentadienylplatinum-trimethyl,9,10 was used to deposit platinumco
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