Fabrication of complex three-dimensional multilevel silicon micro- and nano-structures

S. Azimi
National University of Singapore, SG

Keywords: silicon micro/nano fabrication, three dimensional (3D), porous silicon, curved, free-standing, multilevel

Summary:

We have developed a new process to fabricate arbitrary-shaped, multilevel, three-dimensional free-standing micro- and nano-structures on bulk silicon using focused high energy proton beam irradiation, followed by electrochemical anodization. We make use of the fact that high-energy protons create significantly more localized defects at their end–of-range than close to the surface. By controlling the fluence of an irradiated area, the resistivity can be controlled and increased locally for selective porous silicon (PSi) formation during subsequent electrochemical anodization. As a result PSi forms around irradiated regions, leaving the core region intact.This has enabled us to produce complex free-standing micro/nanostructures such as arrays or long wires, grids, wheels, vertically stacked wires and wires which can be controllably bent upwards and downwards in the vertical plane. We can controllably vary the width of wires from tens of nanometers to tens of microns by varying the fluence of high energy protons and the depth of wires from about 800 nm to 50 µm by varying the proton energy. Similarly gray scale masks enable fabrication of true three-dimensional silicon structures which can vertically curved. By using multiple energy proton irradiation different ion penetration depths and hence multilevel free-standing three-dimensional silicon structures can be obtained.