INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 15 (2004) 158–162 PII: S0957-4484(04)70446-8 Direct writing of ZrO 2 on a sub-10 nm scale using an electron beam K R V Subramanian 1 , M S M Saifullah 1,3 , E Tapley 2 , Dae-Joon Kang 1 , M E Welland 1 and M Butler 2 1 The Nanoscience Centre, Interdisciplinary Research Collaboration in Nanotechnology, University of Cambridge, 11 J J Thomson Avenue, Cambridge CB3 0FF, UK 2 Leica Microsystems Lithography Limited, PO Box 87, Coldhams Lane, Cambridge CB1 3XE, UK E-mail: msms2@eng.cam.ac.uk Received 14 October 2003, in final form 28 October 2003 Published 14 November 2003 Online at stacks.iop.org/Nano/15/158 (DOI: 10.1088/0957-4484/15/1/031) Abstract We describe a direct write technique using an electron beam to pattern ZrO 2 on a sub-10 nm scale that bypasses the conventional method of sputtering and lift-off. This technique utilizes spin-coatable ZrO 2 resist prepared by chemically reacting zirconium n-butoxide with benzoyl acetone in ethanol. The patterned resist has a sensitivity and contrast of ∼40 mC cm -2 and 3, respectively. Baking the resist at 85 ◦ C increases the sensitivity to ∼9 mC cm -2 . The electron-beam-exposed regions become insoluble in acetone, thus yielding negative patterns. This property was exploited to write high-resolution patterns as small as 9 nm wide. Such negative patterns can be written with a pitch as close as 30 nm. 1. Introduction Zirconium dioxide offers advantages of high strength, fracture toughness, wear resistance, high refractive index, low loss in visible and near infrared region [1], heat resistance, chemical inertness, relatively high dielectric constant [2] and oxygen ion conductivity [3]. These properties are used to manufacture oxygen sensors [3], fuel cells [4], optical filters, laser mirrors [5], alternative gate dielectrics in microelectronics [6] and membranes for high-temperature oxygen permeation [7]. The potential for miniaturization of some of these devices is offset by the fact that conventional methods of patterning ZrO 2 using the lift-off technique remain unreliable. The lift-off process is almost always unsuccessful especially when complicated features and thick films of ZrO 2 are desired. In order to overcome this problem, we propose direct writing of ZrO 2 using an electron-beam-sensitive spin- coatable ZrO 2 resist. This resist is capable of direct writing on a sub-10 nm resolution. Spin-coatable ZrO 2 resist was prepared by reacting zirconium n-butoxide, Zr(OBu n ) 4 , with benzoylacetone, BzAc. The resist was found to be stable in air. Electron beam patterning resulted in 9 nm wide lines. Features as small as 10 nm could be patterned on a 30 nm pitch. 3 Author to whom any correspondence should be addressed. 2. Experimental details The desired characteristics in an electron beam resist are good chemical stability and developmental characteristics. In order to optimize the chemical stability of the resist in solution, Zr(OBu n ) 4 (zirconium n-butoxide, 80 wt% solution in 1-butanol, Sigma Aldrich) was reacted with various β -diketones (acetyl acetone and BzAc) and β - ketoesters (methyl acetoacetate, ethyl acetoacetate, isopropyl acetoacetate, isobutyl acetoacetate and isoamyl acetoacetate) in equimolar amounts for 2 h at room temperature inside a glove box (<5% relative humidity). The solvent was ethanol. The solutions were observed for precipitation. It was seen that all β -diketone and β -ketoester-stabilized Zr (OBu n ) 4 gave clear solutions but poor developmental characteristics except for BzAc-stabilized Zr (OBu n ) 4 . The BzAc-stabilized Zr(OBu n ) 4 gave a clear solution and developed easily in acetone. As a result, only this combination was chosen for further experimental studies. BzAc-stabilized Zr (OBu n ) 4 solution was diluted in 1-pentanol and spin-coated on pre-cleaned SiO 2 /Si wafers. Resist thickness was measured using an EL X-02 C DRE GmbH ellipsometer. One set of coated wafers was baked at 85 ◦ C for an hour. The exposure characteristics of the resists were studied using a modified JEOL 4000EX nanowriter 0957-4484/04/010158+05$30.00 © 2004 IOP Publishing Ltd Printed in the UK 158