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

The technology of high‐resolution focused ion beams has advanced dramatically in the past 15 years as focusing systems have evolved from laboratory instruments producing minuscule current densities to high current density tools which have sparked an important new process: direct micromachining at the micrometer level. This development has been due primarily to the exploitation of field emission ion sources and in particular the liquid‐metal ion source. Originally developed in the early 1960’s as a byproduct of the development of electrostatic rocket engines, the liquid‐metal ion source was adapted for focused beam work in the late 1970’s, when it was demonstrated that submicrometer focused ion beams could be produced with current densities greater than 1 A cm−2. Ions can be produced with liquid‐metal ion sources from elements including Al, As, Au, B, Be, Bi, Cs, Cu, Ga, Ge, Fe, In, Li, P, Pb, Pd, Si, Sn, and Zn. In the past decade, focused ion beam systems with liquid‐metal ion sources have had a signific...

High‐resolution focused ion beams

Review: Developments in micro/nanoscale fabrication by focused ion beams

Multilayer Laue lens (MLL) is a new class of x-ray optics that offer great promise for achieving nanometre-level spatial resolution by focusing hard x-rays. Fabricating an MLL via thin-film deposition provides the means to achieve a linear Fresnel-zone plate structure with zone widths below 1?nm, while retaining a virtually limitless aspect ratio. Despite its similarity to the Fresnel-zone plate, MLL exhibits categorically distinctive focusing properties and their fabrication comes with a wide array of challenges. This article provides a comprehensive review of advances in MLLs, and includes extensive theoretical modelling on focusing performance, discussion on fabrication challenges, their current capabilities and notable results from x-ray focusing experiments.

https://iopscience.iop.org/article/10.1088/0022-3727/47/26/263001/pdf

Hard x-ray nanofocusing by multilayer Laue lenses

A focused ion beam (FIB) was applied for cross-sectional sample preparation with both transmission electron microscopes (TEM) and scanning electron microscopes (SEM). The FIB sample preparation has the advantage of high positioning accuracy for cross sections. On the other hand, a broad ion beam (BIB) has been conventionally used for thinning TEM samples. Although both FIB and BIB use energetic ion beams, they are essentially different from each other in many aspects such as beam size, beam current density, incident angle of the beam with respect to cross sections, and beam scanning (i.e., dynamic or static beam). In this study, FIB cross-sectioning is compared with BIB thinning. We review inherent characteristics such as positioning accuracy and uniformity of cross section, radiation damage, and beam heating. Discussion is held from a view-point of ion beam and sample interaction.

Cross-sectional sample preparation by focused ion beam : a review of ion-sample interaction

A 30 kV fine focused ion beammachining system was constructed in which a Ga ion beam extracted from a needle‐type liquid metalsource is focused into a submicron spot by a three‐electrode electrostatic lens and deflected by an octapole deflector. Vacuum rate at the work stage is 10− 7–10− 8 Torr. With blanking electrodes, the machined area can be confined to any rectangular area determined by the cursol lines on the scanning ion microscopic display. Probe current is higher than 0.3 nA for a 0.3 μm diam spot and current density is over 0.71 A/cm2. At a scanning speed of 100 μm/s, grooves 0.2 μm wide are made in a gold film 0.1 μm thick. By scanning repeatedly, a groove is produced in a (100)Si wafer yielding a cross section having a very sharp V shape with an aspect ratio of 8:1. Two‐dimensional scanning removal is performed under various conditions at the same dose of 1.9×101 8 ion/cm2, resulting in very different hole shapes. Removal at a scanning speed of 1 mm/s with 200 repetitions produces a uniform shallow hole shape, while removal at 5 μm/s with one repetition results in an inclined deep hole shape. Observation of the cross section shows that this inclined area protrudes from the side wall of the hole, formed through the redeposition of sputtered silicon. These results show the importance of the redeposition process in removal utilizing fine focused ion beams. Also, the differing results of two scanning methods appear to demonstrate the nonlinear sputter effect in fine focused ion beammachining.

A. Shimase

Papers

Characteristics of silicon removal by fine focused gallium ion beam