Quest for high brightness, monochromatic noble gas ion sources

Abstract

Focused ion beam (FIB) machines are key tools for state-of-the art sample preparation in electron microscopy, for characterization and repair in material sciences, for the semiconductor industry and for nanotechnology in general. Liquid-metal ion sources (LMIS) are widely used in FIB machines because they meet the minimum ion source requirements such as source brightness and reliability. However, in FIB machines, noble gas ion sources are favorable for sputtering, beam-induced etching and deposition, because the implanted ions do not change the electrical behavior of the substrate significantly. There are several efforts by various researchers to develop noble gas ion sources that can be used in FIB machines instead of LMIS. The gas ion sources could not meet the minimum ion source requirements. Therefore, LMIS are still a popular choice among FIB machine users. This review article takes a critical look at the reported efforts in the literature to develop noble gas ion sources for FIB machines.

Helium ion microscopy

“…GFIS have been investigated for a long time 1,[8][9][10] for their use in microscopes. [11][12][13][14] The idea is based on the initial design of a field ion microscope by M€ uller.…”

Focused ion beams for nano-machining and imaging

“…From an optical perspective, the most important parameters to consider for the ion sources are their brightness, angular intensity, and energy spread. The 'reduced' or 'specifi c' brightness B r (A/m 2 × S r × V ) of sources (Tandare, 2005) is defi ned as © Woodhead Publishing Limited, 2014 B I r = δ ΩV [4.1] where I is the source ion current, δ the virtual source size, Ω the solid angle into which the ions are emitted, and V is the acceleration voltage. Reduced brightness is conserved throughout the optical system, so that its value at any focus of the ion beam stays the same irrespective of the imaging conditions.…”

Nano Characterization of Materials

“…Helium ion microscopy is related to field ion microscopy in which a positively-biased sharp tip at cryogenic temperature established a very high electric field at its tip. 30 At high tip electric fields, atoms are field evaporated, but at lower fields neutral atoms near the tip are ionized through electron tunneling and the resulting positive ions are immediately accelerated away from the tip. The emission from a single atom at the source tip is selected with an aperture and the beam current can be modulated by changing the gas pressure, which can be controlled over several orders of magnitude without any need to change the beam energy, aperture, focus, extraction field, or beam steering.…”