Single-crystal silicon nanostructure fabrication by scanning probe lithography and anisotropic wet etching

Silicon nanostructures have been demonstrated by electric-field-enhanced localized oxidation on single crystal silicon wafer using a scanning probe microscope (SPM). In this study, we have demonstrated the use of scanning probe lithography (SPL) and orientation-dependent etching (ODE) can easily obtain nano-wire and nano-gap down to 24 nm and 60 nm on (110)-oriented silicon substrate. The scanning probe lithography (SPL) provides high resolution, which can be adjusted by tip bias, tip set force, scanning speed, and ambient humidity of environment, without damage in the substrate. The etching process employed the orientation-dependent etching (ODE), because of the etching rate of the (111)-plane is slower than any other crystallographic planes such that anisotropic etching profile can be obtained. The experimental samples were hydrogen-passivated by dipping in 10% aqueous HF solution to remove sample native oxide on the surface before SPM localized oxidation process. The SiO_x nano-patterns on (110)-oriented silicon substrate were generated by SPM localized oxidation. Then, the etching process employed the ODE with a 34 wt.% aqueous KOH solution. The nano-wire feature size is easily down to 24 nm and aspect ratio larger than 4:1. The optimization line/space nanostructure is about 20 nm / 80 nm and the nano-gap is about 60 nm. In this study, we also have demonstrated the influence of etching temperature on the feature size of nanostructures with same aspect ratio. At the same etching depth (100 nm), the line-width decreases with increasing the etching temperature. The theoretic etching rate and experimental etching rate are proportional to temperature, the higher temperature the higher etching rate.