ALIS Corporation has developed a new helium ion microscope which has many advantages over both traditional scanning electron microscopes (SEMs) and focused ion beams (FIBs). This new technology is expected to produce an ultimate focused spot size of 0.25nm. This high resolution is attributed to the high source brightness (B>4×109A∕cm2sr), low energy spread (ΔE∕E∼2×10−5), and small diffraction effects (λ∼80fm). The interaction of helium ions with matter offers several valuable contrast mechanisms and a surface interaction volume which is much smaller than a SEM or conventional FIB.

In recent years, helium ion microscopy has produced high resolution images with novel contrast mechanisms. However, when using any charged particle beam, one must consider the potential for sample damage. In this article, the authors will consider helium ion induced damage thresholds as compared to other more traditional charged-particle-beam technologies, as a function of dose, dose rate, and beam energy, and describe potential applications operating regimes.

In order to get high resolution images from any scanning beam microscope one must be able to produce a sufficiently small probe, have a small interaction volume in the substrate and have an abundance of information-rich particles to collect to create the image. A typical scanning electron microscope is able to meet all of these requirements to some degree. However, a helium ion microscope based on a Gas Field Ion Source (GFIS) has significant advantages over the SEM in all three categories.

Articles you may be interested inAnalysis of subsurface beam spread and its impact on the image resolution of the helium ion microscope Recent investigations are gaining us a better understanding of the nature of the beam-sample interactions in the helium ion microscope and what they mean for the image information provided. In secondary electron ͑SE͒ imaging, for example, the surface sensitivity is attributed to the low SE-II fraction. Voltage contrast imaging shows the ability to see both buried structures and to probe the conductance to ground of surface contacts. It is found, however, that the prominence of these two types of contrast varies oppositely with beam energy, yielding information about the nature of the interactions that gives rise to them. Transmission ion imaging can yield information about material density, atomic number, grain structure, and electronic structure. It is possible to capture the top-side SE signal, bright field signal, and dark field signal from a given sample simultaneously. The detection of diffraction contrast is under investigation.

Secondary ion mass spectrometry on the helium ion microscope: A feasibility study of ion extraction J. Vac. Sci. Technol. B 30, 06F602 (2012); 10.1116/1.4754309Effect of sample bias on backscattered ion spectroscopy in the helium ion microscope

Existing techniques for electron- and ion-beam lithography, routinely employed for nanoscale device fabrication and mask/mold prototyping, do not simultaneously achieve efficient (low fluence) exposure and high resolution. We report lithography using neon ions with fluence <1 ion/nm(2), ∼1000× more efficient than using 30 keV electrons, and resolution down to 7 nm half-pitch. This combination of resolution and exposure efficiency is expected to impact a wide array of fields that are dependent on beam-based lithography.

The success of the helium ion microscope has encouraged extensions of this technology to produce beams of other ion species. A review of the various candidate ion beams and their technical prospects suggest that a neon beam might be the most readily achieved. Such a neon beam would provide a sputtering yield that exceeds helium by an order of magnitude while still offering a theoretical probe size less than 1-nm. This article outlines the motivation for a neon gas field ion source, the expected performance through simulations, and provides an update of our experimental progress.

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