Fabrication of arrays of sub-20-nm silica walls via photolithography and solution-based molecular coating

We report herein fabrication of arrays of sub-20-nm silica walls via photolithography and the surface sol-gel process. A photolithographically fabricated line template on a silicon wafer was coated with a silica nanolayer using the surface sol-gel process, and then the topmost portion of the silica layer and the template were successively removed using CHF₃ and oxygen plasma, respectively, leaving the sidewalls of the silica layers remaining on the substrate. These walls were fully self-supporting, and the thicknesses of silica wall were 6, 8, and 12 nm at 20, 30, and 60 cycles, respectively. The height/width ratio of the wall was 38 at the 30-cycle coating. This ratio is surprisingly high when compared to that of the conventional photolithography processes. Successive formation of the silica, polymer, and silica layers yielded a trilayer sidewall, and the spacer polymer layer could be selectively removed to form a doubled sidewall. Size reduction and proliferation of sub-20-nm silica wall was thus achieved. The reported method is simple and cost-efficient and opens a gateway to further miniaturization of nanostructures.