Measurement and simulation of impinging precursor molecule distribution in focused particle beam deposition/etch systems Ivo Utke a, * , Vinzenz Friedli a,b , Simone Amorosi b , Johann Michler a , Patrik Hoffmann b a Nanomechanics and Nanopatterning Group, EMPA Materials Science and Technology Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland b Advanced Photonics Laboratory, Ecole Polytechnique Fe ´de ´rale de Lausanne (EPFL), 1015 Lausanne, Switzerland Available online 20 February 2006 Abstract The distribution of metal-precursors supplied via a gas injection system to the substrate inside a focused electron beam (FEB) induced deposition system is investigated for the first time. The impinging precursor molecules are thermally decomposed using a heating stage. Resulting deposit thickness profiles obtained from [(PF 3 ) 2 RhCl] 2 , Co 2 (CO) 8 , and (hfac)CuVTMS precursors are determined optically by interference colors or by profilometry. FEB access to the precursor flux peak and the flux peak value itself depend on tube tilt and vertical tube distance to the substrate. Monte Carlo simulation match best the experiments when assuming molecular flow conditions. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Gas injection system; Precursor distribution; Effusion; Focused electron beam; Focused ion beam; Deposition; Etching 1. Introduction Focused particle beam induced deposition/etch systems use mostly microtube based gas injection systems to supply the volatile precursor to the reaction region as shown sche- matically in Fig. 1. The overall area where precursor mol- ecules impinge is often millimeter size and little is known about the precursor density at the nanometer sized deposi- tion/etch spot. The precursor density determines whether the process is electron or precursor limited. These regimes, or more precisely the ratio between adsorbed precursor flux and charged particle flux (electrons or ions) at the deposi- tion/etch area crucially determine the deposition and etch rate [1,2], minimum dot dimensions at nano-scale [3], the shape [4], the metal content and electrical resistivity [5], and mechanical properties [6]. Fundamental studies to above topics thus require the knowledge of the precursor density at the areas where the focused particle beam hits the substrate. The impinging flux strongly determines this value and is the subject of this article. The overall flow rate of tube-based supply systems can be experimentally determined by mass or volume loss mea- surements and allows average flux values at the tube exit to be deduced. The average precursor flux arriving on the sub- strate as a function of vertical microtube distance was mea- sured using stagnation tubes [7] and as a function of temperature using quartz microbalances [1]. A microme- chanical gas sensor together with a geometrical approach to estimate the average precursor flux on the substrate was reported in [8]. Recently, the distribution of impinging water molecules was measured on a cryo-cooled substrate inside a dual beam system and modeled solving numerically the contin- uum Navier–Stokes equation [9]. Our approach presented in this paper relies on the ther- mal decomposition of impinging precursor molecules being analogous to chemical vapor deposition (CVD) driven in the precursor flux limited regime. For the first time spatial distributions of FEB relevant precursors containing cop- per, rhodium, and cobalt could be accessed under typical injection conditions. A comparison with Monte Carlo sim- ulations taking into account molecular and transient flow conditions is presented. 0167-9317/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2006.01.136 * Corresponding author. Tel.: +41 33 2282957; fax: +41 33 2284490. E-mail address: ivo.utke@empa.ch (I. Utke). www.elsevier.com/locate/mee Microelectronic Engineering 83 (2006) 1499–1502