Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Carving New Frontiers for Ion-Beam Technology


Plasma is formed in both chambers of the two-chamber device, but potentials on the three electrodes between the chambers ensure that only electrons exit the left chamber, while positive ions are kept out. The positive beam is formed in the chamber on the left, and both beams are extracted by the accelerator column, far right.

An Imprinter that Combines Electron and Ion Beams Opens the Way for Wider Applications

An ion-beam system that simultaneously combines focused beams of electrons and positive ions promises to improve the versatility, efficiency, and economy of this important technology. The new system was developed by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory, who report its principles and applications in the November 8, 2004 issue of Applied Physics Letters.

Focused ion beams are important in the semiconductor industry, where they are used to carve structures with dimensions measured in billionths of a meter, repair defects in masks used for photolithography, isolate and analyze elements of integrated circuits, "dope" semiconductors with specific atomic species, and perform other tasks.

Focused ion beams have also been used to create images of surfaces, pattern thin films for dense magnetic storage, analyze the chemical content of samples, and investigate biological systems. And because ion beams can shape materials with microscopic precision, they can micromachine miniature medical implants, such as cardiac stents that hold weak blood vessels open.

Complicating these applications, however, is the fact that "problems arise when positive ions are used for imaging or micromachining insulating materials," says Qing Ji, who authored the Applied Physics Letters report with her colleagues Lili Ji, Ye Chen, and Ka-Ngo Leung.

Qing Ji is a postdoctoral fellow in the Center for Imaging and Mesoscale Structures at Harvard University and a guest at Berkeley Lab. Coauthors Lili Ji and Chen are with Berkeley Lab’s Accelerator and Fusion Research Division (AFRD) and the Department of Nuclear Engineering at the University of California at Berkeley, as is Leung, who heads the Plasma and Ion Source Technology Group in AFRD. The trouble with using positive-ion beams on insulating samples, Ji explains, is that "the target material is charged by the positive ions; as the positive charge builds up on the sample it repels the ions and defocuses the beam."

Traditionally two methods have been used to keep a nonmetallic sample from acquiring charge from a positive-ion beam, she says. "One method is to pass the beam through a gas cell, where it is partially neutralized before it reaches the sample by acquiring electrons from the gas. The other is to train a separate beam of electrons on the sample." Both have significant disadvantages. A gas cell may require too much distance between the beam accelerator and the sample, which can interfere with beam focusing. And a separate electron beam requires a separate accelerator, which must be precisely aligned with the ion beam at all times. If the ion beam is scanning the sample, this can be difficult; if multiple ion beamlets are being directed at the sample simultaneously, it’s virtually impossible.

"In fact our new beam system was inspired by one of our group’s previous inventions, a multiple-ion-beam system that can steer hundreds of beamlets simultaneously," says Ji. "The device had no room for a neutralizing gas cell, and there was no way to use a separate electron beam to neutralize the sample."

A new way to neutralize ion beams

The group came up with a novel solution: instead of a liquid-metal ion source, standard in many focused ion beam devices, the new system uses two chambers in which plasma is generated by radio-frequency electromagnetic fields, which separate gas molecules into their component electrons and positive ions. The two chambers are divided by an arrangement of electrodes that allows only high-energy electrons to exit the first chamber and at the same time keeps positive ions out.

In the second chamber an ion beam is formed and accelerated by a lower voltage, which does not impede the high-energy electron beam. Both beams combine in a single mixed beam and are extracted by the accelerator column. The self-neutralizing, mixed beam stays tight on its way to the target, because with electrons present there is little "space charge" — the positive ions do not push one another apart — nor does it charge the sample upon striking it.

The combined-beam system can accelerate numerous species of ions, including noble gases like argon, metals like manganese, and even molecular ions like carbon-60 "buckyballs," useful in biological studies because of their stability. In proof-of-principle experiments, the researchers used perforated stencil masks as the forward electrode of the accelerator, causing the beam to transfer the stencil’s distinct shapes to the sample.

The dimensions of the shapes could be altered dramatically by establishing an electrostatic field between the mask and the sample. The researchers used argon ions to sputter stainless steel foils with an arc shape, the same length but more than twice as narrow as the aperture in the mask. In another experiment with an oxygen-ion beam, they cut trenches into a graphite sample three times narrower than the mask aperture.

The same technique can be used with three-dimensional masks, for example a cylindrical mask that accelerates surrounding electron and ion plasma to carve out features in a cardiac stent. Ka-Ngo Leung points out the advantages: "There’s no need for scanning, no need to rotate the target. Unlike the way cardiac stents are manufactured now — one at a time, machined by a laser — ion-beam imprinting would allow hundreds or thousands of stents to be produced with just one shot."

Other current industrial applications that could benefit from imprinting with electron/positive-ion beams include, says Leung, "sound suppressors for jet engines that require millions of holes, which could be produced in one shot. Or cutting the many trenches needed to increase surface area in hydrogen fuel-cell electrodes, which could also be done in one shot."

In these and many other industrial applications involving micromachining, most of which currently employ laser systems, combined electron/positive-ion beams offer an economical way to greatly increase efficiency and throughput. "A combined electron and ion beam imprinter and its applications," by Qing Ji, Lili Ji, Ye Chen, and Ka-Ngo Leung, appears in the November 8, 2004 issue of Applied Physics Letters. Principal funding for the combined-beam project was provided by the Defense Advanced Research Projects Agency’s Advanced Lithography Program.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Paul Preuss | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Basque researchers turn light upside down
23.02.2018 | Elhuyar Fundazioa

nachricht Attoseconds break into atomic interior
23.02.2018 | Max-Planck-Institut für Quantenoptik

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>