3D structuring of c-Si using porous silicon as sacrificial material

A new three dimensional structuring technique for crystalline silicon is investigated. Using porous Si with a typical pore size of a few nanometers three dimensional shapes can be formed. The shape of the structures is provided by an anodisation process in which crystalline Si is transformed to nanoporous Si. Control of the local depth of the 3D structures is achieved by appropriate 2D masking structures and the resulting current density distribution. Thus the process allows the transfer of a 2D pattern into a 3D structure in a single step. Subsequent electro-polishing provides optically smooth surfaces of the etched structures which makes this technique interesting for micromold applications e.g. for the fabrication of optical elements.