[7p-C13-1~9] Recent GFIS /advanced ion source microscopy technologies and its future prospects for R & D of materials and devices

▲ [7p-C13-3] The Physics of Helium Ion Nano-structuring

〇William Bond Thompson¹ (1.Heelionics LLC)

Keywords:Helium Ion, Nanofabrication, Molecular Dynamics

The classical, quantum mechanical and Born approximation derivations of Rutherford backscattering and recoil scattering in a pure Coulomb field produce identical cross sections¹. We used the classical carbon recoil cross sections to accurately predict the helium ion dose required to eject one carbon atom from single sheet graphene, a testimonial to Rutherford’s theory. An ion-beam molecular dynamics (MD) simulator, Kalypso², allowed us to learn what minimum geometries helium ions incident on graphene and atomically thin silicon nitride films might generate. For the helium ion nano-structuring of thin crystalline foils, we have used the CIF crystal data for the film of interest as input to Kalypso to simulate the results of some helium ion microscope (HIM) experiments. A comparison of these results to existing experiments will be made. Since there are a considerable number of helium ion nano-structuring applications³, it seemed important to learn more of their capabilities and limitations. For example, 1) Will the Debye-Waller thermal motion of the target atoms participate in a nanopore’s minimum dimension? 2) What role do beam size and beam noise factors play in a nano-structure’s geometry? 3) Why do helium ions incident on a gold film produce higher aspect ratio holes than those incident on a silicon film? 4) For a sample of finite thickness, what dose rate will produce sample evaporation rather than sputtering? Our talk will attempt to provide answers to these questions. To answer the thermal questions, we have used SRIM⁴ and the physics simulator, COMSOL⁵, to study the helium ion energy, power and temperature distributions in samples irradiated by helium ions at varying dose rates, see figure 1 as an example of helium ion energy loss in silicon. Our presentation should provide the audience with an overview of the factors important in determining the three-dimensional characteristics of nano-geometries patterned with helium ions.