Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.

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Gas-assisted focused electron beam and ion beam processing and fabrication

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

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

A chamber for exposing a workpiece to charged particles includes a charged particle source for generating a stream of charged particles, a collimator configured to collimate and direct the stream of charged particles from the charged particle source along an axis, a beam digitizer downstream of the collimator configured to create a digital beam including groups of at least one charged particle by adjusting longitudinal spacing between the charged particles along the axis, a deflector downstream of the beam digitizer including a series of deflection stages disposed longitudinally along the axis to deflect the digital beams, and a workpiece stage downstream of the deflector configured to hold the workpiece.

Apparatus and method for controlled particle beam manufacturing

We report on the fabrication and electrical characterization of functionalized solid-state nanopores in low stress silicon nitride membranes. First, a pore of approximately 50 nm diameter was drilled using a focused ion beam technique, followed by the local deposition of silicon dioxide. A low-energy electron beam induced the decomposition of adsorbed tetraethyl orthosilicate resulting in site-selective functionalization of the nanopore by the formation of highly insulating silicon oxide. The deposition occurs monolayer by monolayer, which allows for control of the final diameter with subnanometer accuracy. Changes in the pore diameter could be monitored in real time by scanning electron microscopy. Recorded ion currents flowing through a single nanopore revealed asymmetry in the ion conduction properties with the sign of the applied potential. The low-frequency excess noise observed at negative voltage originated from stepwise conductance fluctuations of the open pore.

/pdf/fabrication-and-functionalization-of-nanochannels-by-22vmjy10k5.pdf

Fabrication and functionalization of nanochannels by electron-beam-induced silicon oxide deposition.

A new macroscopic model for focused ion beam induced surface chemistry is presented. The model consists of two parts. The first part is based on previous work by several authors and assumes a uniform current distribution for the ion beam. In this case an analytical solution for the reaction yield can be obtained. Compared to previous work, the new model shows an improved agreement with experimental data and delivers physically meaningful parameter values. In an extended model a Gaussian beam shape has been used to account for the spatial and temporal variations in the current distribution, which are present in a real focused ion beam system. In this case the analytical solution for the yield dependence has to be solved using a spatially depended ion flux and integrated over the whole area of the pixel, which was done numerically. This model shows very good agreement with experimental data and delivers a consistent set of parameters values. In addition, experimental changes in parameter values such as beam size (defocusing) and pixel step size are accurately reflected in the simulation.

Thomas Kraus

Papers

Modeling of focused ion beam induced surface chemistry

Modeling of focused ion beam induced chemistry and comparison with experimental data