Metal-catalyzed etching of vertically aligned polysilicon and amorphous silicon nanowire arrays by etching direction confinement

A systematic study of metal-catalyzed etching of (100), (110), and (111) silicon substrates using gold catalysts with three varying geometrical characteristics: isolated nanoparticles, metal meshes with small hole spacings, and metal meshes with large hole spacings is carried out. It is shown that for both isolated metal catalyst nanoparticles and meshes with small hole spacings, etching proceeds in the crystallographically preferred <100> direction. However, the etching is confined to the single direction normal to the substrate surface when a catalyst meshes with large hole spacings is used. We have also demonstrated that the metal catalyzed etching method when used with metal mesh with large hole spacings can be extended to create arrays of polycrystalline and amorphous vertically aligned silicon nanowire by confining the etching to proceed in the normal direction to the substrate surface. The ability to pattern wires from polycrystalline and amorphous silicon thin films opens the possibility of making silicon nanowire array-based devices on a much wider range of substrates. Metal-catalyzed etching with patterned metal meshes having different geometries was used to control the orientations of silicon nanowires. Specific conditions for fabrication of nanowires with axes normal to the substrate surface, regardless of the crystallographic orientation of the substrate, were determined. This allowed use of metal-catalyzed etching to fabricate vertically aligned polycrystalline and amorphous silicon nanopillar arrays from deposited films.