Silicon Nanomachining by Scanning Probe Lithography and Anisotropic Wet Etching

Nanofabrication and fabrication of nanodevices on single-crystal silicon have been demonstrated by electric-field-enhanced local oxidation on semiconductor materials using a Scanning Probe Microscope (SPM). The advantages of the SPM lithography technique are its high resolution and absence of radiation damage in the substrate to be patterned. Scanning Probe Lithography (SPL) is highly dependent on tip bias, tip force, scanning speed and air humidity of the patterning environment. With multi-pixel scanning of SPL, we can control the pattern width and pattern height of local oxidation and then transfer these patterns onto the silicon substrate with wet etching. We have successfully demonstrated accurate linearity control of nanostructures fabrication for different linewidth from 25 to 77 nm by SPL technique. The resistivity of silicon substrate is around 1~10 ohm-cm. The diameter of silicon SPM tip is around 10 nm. Samples were hydrogen-passivated by dipping in 10% aqueous HF solution for 15 sec to remove surface native oxide before performing SPM local oxidation process. Then, anisotropic wet etching process was followed with a 34 wt.% aqueous KOH solution at 40°C for 45 sec. Utilizing the Orientation-Dependent Etching (ODE) of crystallographic planes and additional acoustic agitation, surface roughness can be reduced down to 3.28 nm, which is very close to that of RIE dry etching. Based on SPL and KOH wet etching techniques, EUV gratings nanostructures were demonstrated.