[16p-315-1~11] Recent GFIS microscopy technology and its future prospects for R & D of materials and devices

▲ [16p-315-11] Interaction of gas field ionized nitrogen with silicon

〇(P)Marek Edward Schmidt¹, Xiaobin Zhang¹, Yoshifumi Oshima¹, Le The Anh¹, Anto Yasaka², Teruhisa Kanzaki¹, Manoharan Muruganathan¹, Masashi Akabori¹, Tatsuya Shimoda¹, Hiroshi Mizuta¹ (1.JAIST, 2.Hitachi High-Tech Science Corp.)

Keywords:Nitrogen, Molecular Dynamics

A larger number of gas molecules (among them hydrogen, helium, nitrogen and neon) can be ionized by the gas field ion source (GFIS) and used as projectiles in focused ion beam (FIB) systems. Among them, the nitrogen stands out as it forms a very strong covalent bond. It is not yet fully understood how this N₂ molecule behaves during gas field ionization and sample interaction, i.e. if the bond is broken during ionization. The mass spectrum of electron ionized N₂ gas shows a small amount of N⁺ and a larger amount of N₂⁺. Here, we report scanning transmission electron microscopy (STEM) analysis of cross sections extracted from silicon bombarded with gas field ionized N₂ molecules with a line dose from 0.24 and 9.5x10³ ion/nm. The extracted implantation depths for ion energies of 25 and 16 keV are compared with theoretical values and suggest that the bond sustains the field ionization and is broken during sample interaction. We use first principle molecular dynamics simulation to support this finding (Figure 1b), in particular that the covalent bond is broken within the first few atomic layers of the impinged silicon target.