The Helium Ion Microscope: New Bottom-up Approach To Three-dimensional Nanostructures

A routinely obtained, excellent imaging resolution (0.35 nm) makes the recently commercialized helium ion microscope (HIM) an outstanding tool among scanning charged-particle-beam microscopes. Its direct patterning capability makes it even more exceptional. Reporting in Nanotechnology, researchers demonstrate HIM’s unique patterning resolution (3.5 nm half pitch of gratings) and characteristics. These include precise position and accurate height, and the fabrication of three-dimensional nanostructures free of resist, etch, mode and precursor. During the helium ion bombardment of a Si surface, implantation outperforms milling due to the small mass of the helium ions. This produces tumefaction instead of depression in the Si surface. Under appropriate conditions, a linear dependence of the surface swollen height on the ion doses can be observed.

Taking advantage of the linear relation
Nanopyramids and nanocones are fabricated by gradually increasing the ion dose from the perimeter to the center of the square and circle, respectively. This new type of three-dimensional nanofabrication is easily achieved through direct-write with a helium ion beam and by precision-control of their implantation. It promises new applications in nanoimprint mold fabrication and photomask clear defect reparation. These nanostructures are also found to be very stable at room temperature over a long period of time.

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