Nanotechnology 10 (1999) 458–463. Printed in the UK PII: S0957-4484(99)03532-1 Atomic force microscopy lithography as a nanodevice development technique * A Notargiacomo†, V Foglietti‡, E Cianci§, G Capellinik, M Adami†, P Faraci†, F Evangelisti‡k and C Nicolini¶ † Polo Nazionale Bioelettronica, Via Roma 28, 57030 Marciana (Li), Italy ‡ Istituto di Elettronica dello Stato Solido (IESS), CNR, Via Cineto Romano 42, 00156 Roma, Italy § Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy k Unit` a INFM, Dipartimento di Fisica ‘E Amaldi’, Universit` a di Roma TRE, Via Vasca Navale 84, 00146 Roma, Italy ¶ Institute of Biophysics, University of Genoa, Corso Europa 30, 16132 Genova, Italy E-mail: notargiacomo@iess.rm.cnr.it Received 19 April 1999, in final form 9 August 1999 Abstract. Nanoscale science and technology is today mainly focused on the fabrication of nanodevices. Our approach makes use of lithography processes to build the desired nanostructures directly. The fabrication process involves an electron-beam lithography technique to define metallic microstructures onto which nanometre scale patterning is performed using an atomic force microscope (AFM) as a mechanical modification tool. Both direct material removal and AFM-assisted mask patterning are applied in order to achieve the smallest possible separation between electrode pairs. The sample preparation involves a polymer deposition process that results in conformal growth and in surface roughness comparable to that of the substrate. The results of the application of this technique show that the process is reproducible and exhibits a good operation control during the lithographic steps, both ensured by the imaging facilities of the AFM. The nanolithography technique has been used to fabricate nanogap electrodes to be used for molecular devices. The study reported here can be considered as a reliable starting point for the development of more complex nanodevices, such as single-electron transistors. 1. Introduction Recently, much effort has been made in the field of nanotechnology for the development of nanodevices, due to interests in both fundamental physics (low-dimension structures, single charge effects, etc) and applied research (ultralarge-scale integration, high-density memory storage, etc). The next generation of new devices will require a circuit patterning resolution and a positioning accuracy ranging beyond the limits of the present fabrication processes. However we must consider that industrial processing and analysis techniques, such as optical and electron-beam lithography and scanning probe microscopy (SPM), will not easily be replaced by completely new solutions. A practical way consists in an optimization of the above-mentioned techniques to take advantage of their peculiar features. In particular, the integration of conventional lithography processes with SPM-based techniques allows the definition of circuit patterning down to a nanometre scale. This represents a promising way towards the fabrication of new concept * This paper is based on work presented at the First ELBA Foresight Conference on Molecular Nanotechnology (14–16 April 1999, Rome, Italy). devices for electronic application and the improvement of conductivity measurement techniques, even on a molecular scale. Applying different principles, several attempts were made using SPM to induce modification of oxides, semiconductors and metals on the nanometre scale: low- energy exposure of resists [1], thermo-mechanical writing [2], local oxidation [3, 4], mechanical modification [5] and nanomanipulation [6]. The atomic force microscope (AFM) nanolithography technique takes advantage of the imaging facility and the ability of moving a probe over the sample surface in a controllable way. In the next paragraph we report on the investigation of direct writing, where the AFM probe ‘scratches’ a metal stripe. For ‘scratching’ we mean the mechanical action of the tip that is used as a sharply pointed tool in order to produce fine grooves. The direct scratching is possible with high precision but low-quality results are obtained due to probe wear during the lithographic process. Another solution is the addition of a soft resist polymer, in general spun PMMA, as a mask for the etching processes, thus reducing tip damage but precluding an accurate alignment to the structures underneath. 0957-4484/99/040458+06$30.00 © 1999 IOP Publishing Ltd