The application of focused ion beam (FIB) technology in microfabrication has become increasingly popular. Its use in microfabrication has advantages over contemporary photolithography or other micromachining technologies, such as small feature resolution, the ability to process without masks and being accommodating for a variety of materials and geometries. An overview of the recent development in FIB microfabrication technology is given. The emphasis will be on direct milling, or maskless techniques, and this can distinguish the FIB technology from the contemporary photolithography process and provide a vital alternative to it. After an introduction to the technology and its FIB principles, the recent developments in using milling techniques for making various high-quality devices and high-precision components at the micrometer scale are examined and discussed. Finally, conclusions are presented to summarize the reviewed work and to suggest the areas for improving the FIB milling technology and for future research.

https://iopscience.iop.org/article/10.1088/0960-1317/14/4/R01/pdf

Recent developments in micromilling using focused ion beam technology

This paper reviews the applications of focused ion beam (FIB) sputtering for micro/nano fabrication. Basic principles of FIB were briefly discussed, and then empirical and fundamental models for sputtering yield, material removal rate, and surface roughness were presented and compared. The empirical models were more useful for application compared to fundamental models. Fabrication of various micro and nano structures was discussed. Trimmed atomic force microscope (AFM) tips were tested in measurement and imaging of high aspect ratio nanopillars where higher accuracy and clarity were observed. Micromilling tool fabricated using FIB sputtering was used to machine microchannels. Slicing and dwell time control approaches on FIB sputtering were presented for the fabrication of three dimensional microcavities. The first approach is preferred for practical applications. The maximum aspect ratio of 13:1 of the microstructures was achieved. The minimum size of the nanopore was in the range of 2–10 μm. Cavities of microgear of 70 μm outside diameter were sputtered with submicrometer accuracy and 2–5 nm average surface roughness. The microcavities were then filled with polymer in a subsequent micromodling process. The replicated microcomponents were inspected with scanning electron microscope where faithful duplication of accuracy and surface texture of the cavity was observed.

A review of focused ion beam sputtering

We report the fabrication of nanometric, conformal, smooth dielectric coatings on the ends of apertureless near-field optical probes by both ion beam and electron beam assisted deposition techniques (IBAD and EBAD). The ion beam provides a higher SimOn growth rate than the electron beam, though the undesirable implantation of Ga ions may outweigh the benefits of rapid growth. Wavelength dispersive x-ray spectroscopy reveals that the electron beam deposited dielectric has a stoichiometry of SinO2n. We present two near-field optics applications of EBAD and IBAD grown dielectric layers. EBAD deposited coatings can be used to reduce fluorescence quenching in apertureless near-field scanning optical microscopy, while IBAD fabricated structures are suited for micro/nano-optics.

Ion and electron beam assisted growth of nanometric SimOn structures for near-field microscopy

Recent photonic device structures, including distributed Bragg reflectors (DBRs), one-dimensional (1-D) or two-dimensional (2-D) photonic crystals, and surface plasmon devices, often require nanoscale lithography techniques for their device fabrication. Focused ion beam (FIB) etching has been used as a nanolithographic tool for the creation of these nanostructures. We report the use of FIB etching as a lithographic tool that enables sub-100-nm resolution. The FIB patterning of nanoscale holes on an epitaxially grown GaAs layer is characterized. To eliminate redeposition of sputtered materials during FIB patterning, we have developed a process using a dielectric mask and subsequent dry etching. This approach creates patterns with vertical and smooth sidewalls. A thin titanium layer can be deposited on the dielectric layer to avoid surface charging effects during the FIB process. This FIB nanopatterning technique can be applied to fabricate optoelectronic devices, and we show examples of 1-D gratings in optical fibers for sensing applications, photonic crystal vertical cavity lasers, and photonic crystal defect lasers.

Focused Ion Beam Nanopatterning for Optoelectronic Device Fabrication

Theoretical modelling and analysis of the material removal characteristics in fluid jet polishing

The design, microfabrication and testing of diffractive optical elements (DOE's) with continuous relief used for fiber coupling are discussed in detail. DOE's with diameters as small as 50 mm are fabricated by means of focused ion beam (FIB) technology. A focused Ga+ ion beam is used to mill a continuous relief microstructure at a 50 kV acceleration voltage. The optical performance of DOE's made in this way was compared with that of DOE's fabricated by other methods. The focusing performance of DOE's fabricated with three and six annulus by FIB milling was investigated. Testing of the system which has a coupling efficiency of -1.25 dB (75%) shows that the design meets the application's requirement for fiber coupling, and that DOE's manufactured by our FIB technology are practicable. Compared with a conventional fiber coupling system that uses a plano - convex lens, our system has the advantages of simplicity, short focal length, low cost for the lens and high coupling efficiency.

Diffractive optical elements with continuous relief fabricated by focused ion beam for monomode fiber coupling

Combined with experimental milling, three-dimensional (3D) microfabrication by focused ion beam (FIB) technology has been studied. Rules among limiting aperture size, dwell time, retrace time, tail of Gaussian distribution, etc., have been analyzed in terms of experimental results. Some phenomena are explained from the theoretical point of view. In addition, influence of redeposition for the sidewall root of microstructure in the process of milling is analyzed, and the avoidance methods are used in the meantime. It was proved by experiment that beam current (representing ion beam energy) and beam spot size play an important role in the etching process. Nonlinear variation of these parameters led to the broadening of edge periphery and redeposition at the root of the sidewall. On the other hand, milling order is vital for the 3D microfabrication result by FIB sputtering due to the redeposition effect and profile broadening effect.

Fu Yongqi

Papers

Diffractive optical elements with continuous relief fabricated by focused ion beam for monomode fiber coupling

Experimental study of three-dimensional microfabrication by focused ion beam technology

Investigation of 3D microfabrication characteristics by focused ion beam technology in silicon