Nanofabrication with the Helium Ion Microscope

Helium Ion Microscopy (HIM) [1,2] is best known for its high resolution imaging capabilities of both conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized.
While the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly by small impact parameter collisions.
Here, I first want to summarize results obtained over the last years using focused ion beam induced deposition (FIBID) using the HIM [3]. In addition I will show results on resist writing using the HIM.
Both approaches benefit from the negligible proximity effect in the HIM. This is related to the different energy distribution of the electrons created by the ion beam as well as the near absence of second or higher generation electrons. Consequently, line patterns with a half pitch of 4 nm have been reported [4]. For high aspect pillars this often results in narrow structures created using FIBID as compared to FEBID.
In the second part I will present results obtained using direct write milling low fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic properties of the target material will be altered at the nano-scale in a controlled way to achieve new functionality. The examples comprise • The fabrication of semiconducting graphene nano-ribbons by direct milling [5]

• The fabrication of a lateral spin valve structure using low fluence ion irradiation [6]
• The formation of individual 3 nm Si clusters for a room temperature single electron transistor

For all presented examples the critical length scale of the nanostructure is smaller or in the range of collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation and holds many promises but also challenges that need to be overcome to enable new device concepts and new functional materials on the nano-scale.