Nanoscale direct patterning in ultrathin silicon nanosheets utilizing helium ion microscopy

Abstract Using focused helium-ion irradiation by helium-ion microscopy (HIM), we demonstrated the formation of nanosized hole arrays (nanopore arrays) on ultrathin (<3.6 nm) silicon nanosheets. Nanoscale patterning was conducted by setting the helium ion (He + ) acceleration energy to 30 keV and modulating the ion dose to the irradiated area from 1 × 10 17 to 10 19 cm −1 . The He + irradiated area was observed as a bright spot on the HIM image at a low dose, which changed to an etch pit-like shape as the dose increased. Cross-sectional transmission electron microscopy (XTEM) observations indicated that the nanosheet where the He + was irradiated vanished under the increased dose condition, and the area without irradiation was preserved. Simultaneously, blistering was observed over the entire area where the nanopore array was formed. In the XTEM image, a space was formed between the buried oxide film and the Si layer owing to ion implantation.