New light and heavy ion beams from liquid metal alloy ion sources for advanced nanofabrication and ion implantation.

Focused Ion Beam (FIB) processing has been developed into a well established and still promising technique for direct patterning and proto-typing on the nm scale, high resolution imaging or high resolution ion lithography1. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last fifty years2. Recent developments could make these sources to an alternative technology feasible for nanopatterning challenges.
Concerning ion beam resolution and minimization of unwanted damage, light ions like He or Li are preferred candidates. Liquid metal alloy ion sources (LMAIS) with a life time of more than 1000 µAh on the basis of Ga35Bi60Li5 and Sn95Li5 alloys were developed, characterized and finally applied in a commercial mass-separated VELION FIB-SEM system (Raith GmbH) 3. In the case of Li ions from the mass separated FIB a lateral resolution of 5.6 nm could be obtained in first experiments and the sputter yield was determined to 0.4 for 35 keV Li ions on Au. For reference, the helium ion microscope (HIM) has a lateral resolution of about 0.5 nm and 1.8 nm, for He and Ne respectively, He has a sputter yield of 0.14. For sub-10 nm focused ion beam nanofabrication and microscopy, the GaBiLi-FIB or the SnLi-FIB could therefore be considered alternatives to the HIM with the benefit of providing additional ion species in a mass separated FIB without changing the ion source.
In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented1,5. As an example we will introduce a GaBiLi LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source. Moreover we will discuss the main properties of a modern LMAIS like long life-time, high brightness and stable ion current. The physical basics and experimental results of LMAIS, their physical properties (I-V characteristics, energy spread) and questions of the preparation technology using elementary as well as binary and ternary alloys as source material will be covered.

1 L. Bruchhaus et al. Appl. Phys. Rev. 4, 011302 (2017).
2 L. Bischoff et al. Appl. Phys. Rev. 3, 021101 (2016).
3 W. Pilz et al. J. Vac. Sci. Technol. B 37, 021802 (2019).
4 G. Hlawacek et al. J. Vac. Sci. Technol. B 32, 020801 (2014).
5 J. Gierak et al. J. Vac. Sci. Technol. B 36, 06J101(2018).