Morphological and compositional effects of FIB nanopatterning of multilayer metal/semiconducting devices A. Taurino a,Ã , M. Catalano a , M. Lomascolo a , A. Persano a , A. Convertino b , L. Cerri b a Institute for Microelectronics and Microsystems, Italian National Research Council (CNR-IMM)—Lecce Section, via Arnesano, 73100 Lecce, Italy b Institute for the Study of Nanostructured Materials, Italian National Research Council (CNR-ISMN)—Montelibretti Section, via Salaria Km. 29.300, 00016 Roma, Italy article info Article history: Received 1 December 2008 Accepted 5 December 2008 Available online 13 December 2008 PACS: 81.05.Ea 81.07.Ta 81.16.Rf 68.37.Lp Keywords: FIB nanopatterning Metal-semiconductor multilayer Morphological and analytical investigations TEM EDS HREM abstract In this work, a structural and compositional investigation of the effects of focused ion beam (FIB) nanopatterning of a critical material system was carried out. A pattern of cylindrical holes, with the diameter in the range 50–150 nm, was dug by FIB into the topmost metal layer of an InAs quantum dots based heterostructure, and the effects of the ion beam treatments on the composition of the layers involved in the milling process were evaluated. FIB preparation of transmission electron microscopy (TEM) lamellas provided suitable samples for the chemical analyses exactly from the regions where the holes were dug. Detailed experimental data were obtained by means of scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS), and the effects of implantation, intermixing, redeposition and, more in general, defect creation induced by the Ga ion bombardment evaluated and compared with the results of stopping and range of ions in matter (SRIM) simulations. & 2008 Elsevier B.V. All rights reserved. 1. Introduction FIB nanopatterning is becoming a very wide spreading application of the FIB technology, due to the possibility to process materials of different composition in a single step, with nanometric resolution and without the use of masks [1–6]. Nevertheless, detrimental effects related to the ion beam treat- ment, such as amorphization, implantation, intermixing occur with obvious modifications of the properties of the processed structures [7–12]. This is especially true when anisotropic structures are involved, due to the different interaction effects which can take place when the ion beam propagates through materials with different composition. This is very likely to occur in modern multilayer devices which often include metals as well as semiconductors, with different composition [2,13,14]. For such structures, the effects of the ion beam treatments on the properties of materials and interfaces and then on the operation of the devices can be very critical. In this study, a typical optoelectronic device, including a Ti/Au metal mask on top of the heterostructure and an InAs quantum dot semiconducting multilayer below, has been processed by a 30 keV Ga ion beam in order to obtain a matrix of nanometric holes in the metal mask, with the bottom of the holes at the metal/semiconductor interface. This can find application in many technological and basic research fields. For example, for microphotoluminescence spectroscopy, the holes, dug by FIB in the metal, are used as narrow windows to excite and capture the radiation of ideally a single dot, whereas the ensemble excitation is prevented by the metallic mask [15,16]. On the other hand, technological applications of hole nanopatterning of semi- conducting heterostructures are becoming quite substantial, as demonstrated by the current literature on the fabrication of opto- electronic devices [17]. The effects of the ion beam treatment on the morphological and compositional properties of the heterostructure have been evaluated. In particular, a careful analytical investigation of the nanopatterned device has been carried out by EDS and elemental mapping in a STEM instrument, in order to analyze the effects of the ion bombardment in terms of species interdiffusion, material intermix- ing, layer damage and amorphization. The results of the analytical investigation have been supported by SRIM simulations [18]. 2. Experimental The sample under study included semiconducting epitaxial layers grown by molecular beam epitaxy covered by a metallic ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2008.12.001 Ã Corresponding author. Tel.: +39 0832 422 519; fax: +39 0832 422 552. E-mail address: antonietta.taurino@le.imm.cnr.it (A. Taurino). Physica E 41 (2009) 734–738