Invited Paper HI+NS-ThM3
New Ion Source for Nanofabrication and Microscopy

Thursday, November 10, 2016, 8:40 am, Room 104A

Performance measurements from a recently constructed focused ion beam (FIB) prototype that employs a new ion source technology will be presented. The performance of any FIB system, and hence the tasks to which it is best suited, are typically determined by its ion source. The high brightness and low energy spread of the Low Temperature Ion Source (LoTIS) employed here has the potential to enable significantly smaller focal spot sizes across a range of beam currents and beam energies in an optimized FIB.

The LoTIS consists of a laser-cooled atomic beam of cesium which is compressed and then photoionized within a volume of a few cubic micrometers. A uniform electric field is applied to form an ion beam. The micro-kelvin temperature of the neutral atoms results in a Cs⁺ beam with a low intrinsic transverse velocity spread, yielding low emittance. The small energy spread is determined in this source by the finite spatial extent over which ions are created in a uniform electric field of approximately 10⁵ V/m. Previous measurements have shown was shown that LoTIS can achieve a brightness in excess of 1×10⁷ A m^-2 sr^-1 eV^-1 and an energy spread less than 0.34 eV [1].

This brightness and energy spread imply that, when coupled to an optimized ion acceleration and focusing column, a d₅₀ spot size of 1 nm should be achievable at 1 pA. The source has also achieved total currents over 5 nA, albeit at a reduced brightness. Among other benefits, these source characteristics are expected to enable a FIB with better nanomachining performance and reduced subsurface damage.

The presentation will also briefly discuss FIB equipped with a similar Li⁺ ion source technology that offers a unique capability to site specifically deposit lithium into target substrates.

[1] B Knuffman, AV Steele, and JJ McClelland. J. Appl. Phys. 114, 4 (2013).