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

Probe tips for scanning tunneling microscopy have been sharpened using focused ion beam milling. Reproducible tips were formed on polycrystalline W and Pt‐Ir shanks, but this technique is not limited to these materials. The tips were found to have cone angles of 12±3° and radii of curvature as sharp as 4 nm. Focused ion beam machining allows precise control of the final shape of the tips which is important in metrology measurements of various nanostructure devices.

Scanning probe tips formed by focused ion beams

A mathematical model of focused ion-beam milling is used to generate dwell times for the vector scanned pixel address scheme of a focused ion-beam deflection system. The model incorporates the absolute sputter yield of the solid as a function of the angle of incidence, and the relationship between the ion-beam current distribution and the pixel size of the deflection pattern. The object of this work is to be able to call for an arbitrary geometric shape to be ion milled and then have the numerical model compute the pixel dwell times for the deflection system such that the final cavity is sputtered. Experimental verification of the procedure was accomplished with parabolic troughs, hemispherical troughs, and cosine troughs. The term “trough” means a plane of symmetry in the ion-milled cavity. These same geometric shapes were also ion milled using a rotational axis of symmetry, yielding sinusoidal ring patterns, parabolic dishes, and hemispherical dishes. The absolute maximum depth for each of the cavities ...

Depth control of focused ion-beam milling from a numerical model of the sputter process

This work demonstrates accurate focused ion beam sculpting of micron-scale curved shapes into initially planar solids. Sculpting is accomplished by varying the dose per pixel within individual boustrophedonic scans and accounting for the material-specific angle-dependent sputter yield and the ion beam spatial distribution. We refine this technique by demonstrating how a range of preferred dwell times leads to improved sculpting. An optimized dwell time range is delineated by two effects. Excessively large dwell times lead to enhanced deposition of ejected species, asymmetric milled features (when symmetric features are intended), and depths greater than intended values. These effects occur for dwell times such that the depth removed per pixel in a given scan is on the order of the width of the focused ion beam. On the other end of the dwell time range, inordinately low times lead to undesired ion milling outside targeted areas. Milling outside targeted regions, such as a circle or an ellipse, can occur be...

Accurate focused ion beam sculpting of silicon using a variable pixel dwell time approach

The capability of using a focused ion beam (FIB) for milling of submicron channel structures on a gold layer is investigated. A double-charged arsenic (As2+) FIB is adopted to assess the effect of the dwell time on the final profiles of the milled structures. A single-pass milling, which creates relatively shallow microchannels, is conducted in order to estimate the corresponding milling yields. The condition to provide a uniform ion flux in milling is first studied. The procedure on conducting the milling experiment is then presented. The atomic force microscope (AFM) is applied for measuring the profiles of the milled channels. Based on the AFM measurements, the milling yields have been estimated and compared with the sputtering yields predicted by a more sophisticated numerical simulation. The milling yield for the relatively shallow microchannels presently considered has been discovered to be roughly equal to the predicted normal-incidence sputtering yield. Consistence has also been found as the prese...

Milling of submicron channels on gold layer using double charged arsenic ion beam

Accurate measurement of the beam diameter for a finely focused ion beam is difficult using conventional methods which have been applied in electron beam systems. Generally, the beam is scanned across an abrupt edge while measuring beam current or secondary electron intensity. For ions, the sputtering of the sample degrades the shape of the edge and thus the accuracy of the measurement. Furthermore, implantation can change the secondary electron contrast during the measurement. In this paper, a new method is suggested that avoids these difficulties. The ion beam diameter is determined by measuring the ratio of ion flux in a single pixel wide feature to that of a feature which is much larger than the beam diameter. This ratio can be measured using a threshold process. For this paper, we have used sputtering of a thin film as the threshold process and secondary ion mass spectrometry as the end‐point determinant.

L. R. Harriott

Papers

Beam‐size measurements in focused ion beam systems