REVIEW PAPER Controlling parameters of focused ion beam (FIB) on high aspect ratio micro holes milling Fatin Syazana Jamaludin • Mohd Faizul Mohd Sabri • Suhana Mohd Said Received: 17 June 2013 / Accepted: 5 September 2013 / Published online: 22 September 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Focused ion beam (FIB) direct milling is now recognized as a new method of fabrication, due to high flexibility in milling dimensions, the possible geometries and the material selectivity. This paper discusses the fab- rication of micro holes using FIB direct milling in terms of high aspect ratio structures, including FIB parameters and the major effects of FIB milling. It is deduced that sputter yield of material gives a major impact to the depth of milling. Optimization parameters coupled control of FIB direct milling will provide a precise means of fabricating of high aspect ratio micro holes whilst resolving the problem of re-deposition and amorphisation which is common in micro milling. 1 Introduction The trend towards miniaturization continues as electronic devices tend to be smaller, lighter, thinner and faster with multiple additional functions (Tan 2006). One such development is high density interconnection, which relies on micro-holes to configure multilayer structures and assemble the components on a micro device. Therefore, more functions can be integrated in a compact volume (Wu et al. 2010). Micro-holes, characteristically with microm- eter scale dimensions, are widely used in micro-electro- mechanical systems (MEMS) serving as channels or nozzles to connect two micro-features, such as delivering media in MEMS, or exchanging media outside of MEMS (Yu et al. 2009). Micro holes are also used in micro-fluidic chips for separation of long DNA molecules and for investigation of hydrophilicity and hydrophobicity on nanostructure surfaces (Cheung et al. 2006). The common characteristics of these micro-holes are high aspect ratio, small size and are typically fabricated from hard and brittle materials (Lim et al. 2003). The choice of ‘‘hard’’ materials as required for robust applica- tions, such as fuel nozzles and micro-molds to resist wear, high temperature and high pressure; which have found important applications in products within the aerospace (micro droplet spraying, aerostatic air bearing and filters), automobile and biomedical science industries. However, the diameter of the holes remains large and the holes taper or have irregular inner walls (An et al. 2004). Due to its small diameter of a few microns, high aspect ratio and difficulties in machining part materials, the efficient and steady machining of the micro-holes is a challenging problem (Ziaie et al. 2004). Micro milling is a micro-machining technology used to fabricate materials with complex 3D and high aspect ratio structures. A new method of micro milling is through a set of focused ion beam (FIB) technologies which include FIB direct milling, FIB projection, FIB assisted deposition and FIB implantation. This set of technologies offer opportu- nities especially in controlling material modifications and patterning the critical dimensions in the nanometer regime (Lugstein et al. 2009). Introduced more than a decade ago, FIB was mainly developed during the late 1970s and the early 1980s using liquid metal ion source (LMIS) that have a high brightness of ion source and a very small emitting area, where the ion beam is used to etch the structures (Jacques et al. 2012; Ji 2007). The increasing demand of F. S. Jamaludin (&)  M. F. Mohd Sabri Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia e-mail: fatin.engum@gmail.com S. M. Said Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia 123 Microsyst Technol (2013) 19:1873–1888 DOI 10.1007/s00542-013-1912-y