Abstract
We present measurements of focal spot size and brightness in a focused ion beam system utilizing a laser-cooled atomic beam source of Cs ions. Spot sizes as small as (2.1 ± 0.2) nm (one standard deviation) and reduced brightness values as high as (2.4 ± 0.1) × 107 A m−2 Sr−1 eV−1 are observed with a 10 keV beam. This measured brightness is over 24 times higher than the highest brightness observed in a Ga liquid metal ion source. The behavior of brightness as a function of beam current and the dependence of effective source temperature on ionization energy are examined. The performance is seen to be consistent with earlier predictions. Demonstration of this source with very high brightness, producing a heavy ionic species such as Cs+, promises to allow significant improvements in resolution and throughput for such applications as next-generation circuit edit and nanoscale secondary ion mass spectrometry.
Highlights
Ion beams focused to nanoscale dimensions have become an essential tool for nanotechnology, spanning a wide variety of disciplines ranging from three-dimensional imaging and analysis of samples in biology, geology and materials science, to circuit diagnosis and repair in state-of-the-art semiconductor manufacturing
In this paper we present measurements on a Cs cold atomic beam ion source in a so-called LoTIS configuration [32], demonstrating a brightness well over 2 × 107 A m−2 Sr−1 eV−1— as much as 24 times higher than that seen with the Ga liquid metal ion source (LMIS)—and show spot sizes in the single-digit nanometer range
While resolution can always be improved by increasing ion beam energy, the initial purpose of the prototype is to carry out measurements of spot sizes and convergence angles with the aim of characterizing the source’s brightness
Summary
Ion beams focused to nanoscale dimensions have become an essential tool for nanotechnology, spanning a wide variety of disciplines ranging from three-dimensional imaging and analysis of samples in biology, geology and materials science, to circuit diagnosis and repair in state-of-the-art semiconductor manufacturing. Sources based on ionization of laser cooled atoms have recently attracted attention in the search for higher brightness, access to new ionic species, and overall better performance [16] With this type of source, neutral atoms are cooled using momentum transfer from nearresonant laser light [17] to temperatures in the microkelvin range, and ionized via a focused laser beam to create a very high brightness ion beam. Advantages of this approach include a brightness that does not rely on producing ions from a potentially unstable very sharp tip, an inherently narrow energy spread, and well-developed technology for laser cooling over 27 ionic species, many of which are not addressed with alloy LMIS, GFIS, or plasma sources. Current Cs ion sources used in SIMS have typical brightness [34] in the range of 500 A m−2 Sr−1 eV−1, so the LoTIS could represent a more than 104 fold improvement
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