Direct-Write Atomic Layer Deposition of High-Quality Pt Nanostructures: Selective Growth Conditions and Seed Layer Requirements A. J. M. Mackus, † N. F. W. Thissen, † J. J. L. Mulders, ‡ P. H. F. Trompenaars, ‡ M. A. Verheijen, †,§ A. A. Bol, † and W. M. M. Kessels* ,† † Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands ‡ FEI Electron Optics, Achtseweg Noord 5, 5600 KA Eindhoven, The Netherlands § Philips Innovation Services, High Tech Campus 11, 5656 AE Eindhoven, The Netherlands * S Supporting Information ABSTRACT: Electron beam-induced deposition (EBID) enables the direct-write patterning of metallic structures with sub-10 nm lateral resolution without the use of resist films or etching/lift-off steps but generally leads to material of poor quality and suffers from a low throughput. These shortcomings were mitigated in recent work by combining EBID with atomic layer deposition (ALD). This direct-write ALD technique comprises the patterning of a thin seed layer by EBID followed by selective thickening of the pattern by ALD. In this work, the throughput of direct-write ALD was drastically improved based on new insights into how the ALD growth initiates on EBID material, and in addition, the conditions for selective ALD growth were identified. The required electron dose was reduced by 2 orders of magnitude to ∼11 pC/μm 2 by exposing the EBID seed layers to O 2 in the ALD reactor just before the ALD building step. This improvement of the technique allows for nanopatterning with a throughput comparable to electron beam lithography (EBL). ■ INTRODUCTION With conventional photolithography reaching its limits, there is a need for novel nanomanufacturing methods able to process materials at the nanoscale with precise control over dimensions and material properties. Moreover, it is desirable to eliminate the processing-related elements of manufacturing that may yield compatibility issues with the envisioned nanoscale building blocks of the future, such as nanowires, carbon nanotubes, and graphene. For example, it has been reported that the use of resists films (as is the case in photo- and electron-beam lithography) has a negative effect on the properties of graphene. 1-4 Moreover, the many chemicals involved in the various processing steps of lithography may damage sensitive surfaces. 2 These compatibility issues drive current development of direct-write techniques which do not rely on multistep resist-based processing but are able to deposit material in one single step. Examples of nanoscale direct-write techniques are focused ion beam (FIB) processing, 5,6 dip-pen nanolithography (DPN), 7,8 and electron beam-induced depo- sition (EBID). 6,9 EBID is considered for nanopatterning applications because of its direct-write character and its ability to reach sub-10 nm lateral resolution. 6,9 It relies on local electron beam-induced decomposition of precursor molecules adsorbed on a surface. During EBID, gas molecules are introduced in the electron beam system and adsorb on the surface of the substrate. The electron beam locally induces dissociation of the precursor molecules into volatile and nonvolatile species. The nonvolatile components adhere to the substrate and form the deposit, whereas the volatile species are evacuated from the system. By scanning the electron beam over the surface, a two- or three- dimensional nanostructure can be defined. One of the most important advantages of EBID is that the pattern is written directly and only at the locations where it is desired, which limits the number of processing steps, and eliminates the use of resists or lift-off steps. Because the electron beam can be focused into a spot of less than a nanometer in size, EBID has the ability to pattern material at the nanoscale level. 10,11 For the preparation of metal deposits, the EBID technique has two major drawbacks that currently hamper its applicability, i.e., a poor material quality and a relatively low throughput. Preferably, only the metal atoms form the deposit. However, in practice, high levels of impurities are incorporated when the electron beam-induced dissociation process does not solely lead to volatile reaction products. 12-14 Purity values that are typically obtained are ∼65 at. % for Au from Me 2 Au(tfac) Received: March 5, 2013 Revised: April 15, 2013 Published: April 19, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 10788 dx.doi.org/10.1021/jp402260j | J. Phys. Chem. C 2013, 117, 10788-10798