Study of neutral-beam etching conditions for the fabrication of 7-nm-diameter nanocolumn structures using ferritin iron-core masks

We fabricated nanocolumn structure by using a low energy neutral beam and a ferritin iron-core mask. By using Cl-2 gas plasma for generating neutral beam, we obtained a better etching profile than with SF6 gas plasma. Though Cl-2: SF6 = 90: 10 enabled faster etching than Cl-2 gas without degrading the etching profile when the etching depth was,25 nm, a mixture with any quantity of SF6 gas resulted in a poor etching profile when the etching depth was 50 nm. The beam energy was optimized for the 50-mn depth using Cl-2 gas by changing the rf bias power to the bottom electrode of the neutral-beam source. Using the optimum beam energy, extremely high etching selectivity of the Si to ferritin iron-core masks (about 80) as well as highly anisotropic etching profile could be realized. As a result, the diameter of the top of the Si nanocolumn structure was 7 nm, which was identical to that of the iron core in the ferritin. Additionally, the etching profile was almost vertical. We were also able to achieve a high aspect ratio of about 4.6. It is very difficult for conventional plasma etching processes to fabricate such fine structure, because the high-energy photons enhanced the etching of the iron-core mask in the conventional plasma processes. 0 2005 American Vacuum Society.