Shawn McVey

Subsurface damage from helium ions as a function of dose, beam energy, and dose rate

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.

Neon Ion Beam Lithography (NIBL)

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 Prospects of a Subnanometer Focused Neon Ion Beam

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.

Understanding imaging modes in 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 (SE) 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.

Gas field ion source and liquid metal ion source charged particle material interaction study for semiconductor nanomachining applications

Semiconductor manufacturing technology nodes will evolve to the 22, 15, and 11 nm generations in the next few years. For semiconductor nanomachining applications, further beam spot size scaling is required beyond what is capable by present generation Ga+ focused ion beam technology. As a result, continued Ga+ beam scaling and/or alternative beam technology innovations will be required. In this work, several alternative ion beam technologies are explored and compared to Ga+ beam for key nanomachining and substrate interaction attributes. First, thorough Monte Carlo simulations were conducted with various ion species incident on silicon and copper. Additionally, silicon and copper substrates were experimentally exposed to ion beams of helium, neon, and gallium. These substrates were subsequently analyzed to determine the sputter yields and subsurface damage.

An Introduction to the Helium Ion Microscope.

A new microscope has been developed that uses a beam of helium ions which is focused and scanned across the sample. In principle, and in its applications, it is similar to a traditional scanning electron microscope (SEM). However, the source technology, the sample interaction, and the contrast mechanisms are distinctly different. The helium ion source offers high brightness (4×109 A/cm2sr) and a small energy spread (ΔE/E∼3×10−5), and hence allows the beam to be focused to small probe sizes (as small as 0.25 nm). As the beam interacts with the sample, the beam penetrates relatively deeply before it diverges and hence there is a narrow sample interaction region near the surface. The helium beam generates secondary electrons, scattered helium atoms (ions and neutrals), and other detectable particles from which images can be generated or analysis can be performed.

Nanomachining with a focused neon beam: A preliminary investigation for semiconductor circuit editing and failure analysis

As the semiconductor device scaling trend continues, advancement in both focused ion beam source development and application innovations are needed to retain failure analysis and nanomachining application capabilities. In this work, a neon gas field ionization source was studied for its nanomachining properties. The authors have analyzed neon’s nanomachining precision at 10 and 20 keV on blank Cu and SiO2 thin films. Subsurface material amorphization from neon and its correlation with beam current distribution are characterized by TEM. In addition, some preliminary nanomachining work was performed on a 32 nm test chip and successfully demonstrated end-pointing on various device layers.

The Neon Gas Field Ion Source - Stability and Lifetime

Soon after its development in 1955, the gas field ion source (GFIS) was pursued as the source of positive ions for focused ion beam (FIB) instruments [1]. Within the semiconductor industry, such FIB instruments are of critical importance for their failure analysis (FA), circuit edit (CE), and TEM sample preparation. However the GFIS development efforts were hampered by issues related to the source lifetime, and the short and long term temporal stability. The commercial gallium liquid metal ion source (Ga-LMIS) has served as the ion source of choice for the past 30 years with some recognized shortcomings arising from the probe size, electrical contamination, optical opacity, etc [2]. These shortcomings have produced a growing interest in FIBs with other ion species. In the past decade, the helium GFIS performance was vastly advanced – permitting the development of the helium ion microscope (HIM). In the past year, these same advances were applied to a neon GFIS.

Device metrology with high-performance scanning ion beams

A scanning ion microscope (SIM) is analogous to a scanning electron microscope (SEM) but utilizes a beam of helium ions, with energy of 10 to 25 keV , instead of electrons. The SIM potentially offers several advantages for device critical dimension metrology as compared to the more familiar CD-SEM. These include a high brightness source which is sub-nanometer in size, an enhanced secondary electron yield, restricted beam penetration, and superior image contrast and information content. Possible problems include pervasive positive charging, ion implantation, and a lack of detailed experimental and theoretical knowledge about low energy ion interactions with solids. Comparison of line profiles across structures made by electron induced and ion induced secondary electrons show that there are some significant differences between them which arise from the different modes of interaction in the two cases. As a result the algorithms employed for line width determination will require revision in order to produce data which is consistent with CD-SEM data.

Advantages of Helium and Neon Ion Beams for Intelligent Imaging

Scanning electron microscopy (SEM) has become a crucial tool to visualize the exterior morphology and surface structures for samples in both biology and material science. Conventional SEMs are usually limited by relative low resolution and charging effects. Carbon or metal coating is required for insulator samples to minimize charging effects. However, the coating layer can sometimes obscure miniscule surface details and the coating procedure may generate artifacts, which could be confused with the true ultrastrcuture.