Focused ion beam fabrication of curved structures using the concept of beam shaping and variable dwell time

This paper introduces a technique for the direct fabrication of curved structures using focused ion beams called beam shaping method (BSM). It is based on the concept of variable dwell time and simulations of sputtering and redeposition to shape overall ion dose profile which is composed of individual focused single pixel beam profile. The pixel dwell times are kept small enough to avoid sputtering yield enhancement due to a locally inclined surface. This provides better control over the fabrication process and allows the combination of the individual overlapped beams (separated by the pixel spacing) into a dose profile for use in the simulation. Varying the dwell time at each pixel we optimize the dose profile for the fabrication of the desired structure using repeated simulation. We demonstrate this technique on a silicon substrate by realizing fundamental structures such as circular and triangular optical gratings. The resultant fabricated structures agree well with the desired geometry within tolerance. Detailed explanation of the technique with experimental verifications is given, and the optimized ion dose profiles are discussed.

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