Fabrication of suspended periodic nanostructure by focused ion beam induced material migration and Rayleigh-Plateau instability

This paper shows a fabrication method to form one-dimensional (1D) and two-dimensional (2D) periodic nanostructures on suspended film with focused ion beam (FIB) irradiation. The suspended film is prepared by KOH back etch on the SOI (Silicon-on-insulator) wafer or Si wafer coated with metal or Si₃N₄ film. Then the FIB milling method is applied to pre-define the initial pattern on the suspended film by direct writing. The initial pattern is design with perturbations which will increase during next-stage FIB process and assist the final nanostructure formation. Finally the pre-defined suspended pattern is irradiated by FIB uniformly, and 1D or 2D periodic nanostructures are achieved. We contribute the fabrication mechanism to material migration, which is induced by ion beam bombardment and cascade collision of target material atom, and Rayleigh-Plateau instability, which is driven by surface tension to meet the requirement of minimization of system energy.