Beam-substrate interaction during tungsten deposition by helium ion microscope

We deposited tungsten-based pillars on ~300 nm-thick amorphous carbon and single-crystalline silicon substrates by a helium ion microscope (HIM) using tungsten hexacarbonyl (W(CO)₆) as a gaseous precursor. We then investigated beam-induced damage to the substrates correlated with both pillar growth rate and material type of substrates. Faster pillar growth reduced the substrate damage because the pillars shielded the substrates from the incident beam, resulting in a low-damage process. On the other hand, the Si substrate was significantly damaged by the incident beam compared with the carbon substrates. This is because stopping cross-section of 30-ke V helium ion in silicon is ~1.5 times higher than that in carbon. The incident helium ions were considered to induce the substrate damage in the process of losing energy in the substrates.