Low-damage fabrication of high aspect nanocolumns by using neutral beams and ferritin-iron-core mask

A silicon-nanocolumn structure was fabricated by using neutral beams and a ferritin-iron-core mask. The etching process was observed by scanning electron microscope and x-ray photoelectron spectroscopy (XPS), which revealed that the iron core can be used as an etching mask for more than 30 min of etching. Extrapolation of the XPS results shows that it is possible to fabricate nanocolumns about 180 nm high. The diameter at the top of the nanocolumns was about 7 nm after etching for 5 min or longer, while it was about 12 nm after etching for 2.5 min. It is thus concluded that the current etching condition is applicable for fabricating nanocolumns about 20-180 nm high and 170-nm -high nanocolumn was fabricated. Densely distributed nanocolumns with a narrow gap of 5.5 nm between them could be etched successfully. To demonstrate that nanocolumns can be used for devices and circuits, a regularly arranged nanocolumn array was fabricated successfully. Etching damage was investigated by transmission electron microscope (TEM) and electron-spin resonance (ESR). The TEM observation revealed that the interior and subsurface of the nanocolumns kept a single-crystal structure completely, and no crystalline defects were observed. A small amount of Pb centers were found by ESR measurement and attributed to silicon dangling bonds at the nanocolumn sidewalls. The dangling-bond density was not increased by neutral-beam etching and stayed low (i.e., 2.7× 1011 cm-2) after etching. Damage-free etching was thus achieved by neutral beam. This result may be attributed to the absence of UV photons in the neutral beam. Such a sub- 10-nm process with an arranged pattern and low etching damage has great potential in regard to the development of future nanometer-scale devices.