Silicon Electrochemical Etching for 3D Microforms with High Quality Surfaces

In this paper the process of silicon anodization as a structuring technique is discussed. 3D-structuring is achieved by 3D control of current density in an anodization process. In contrast to conventional ECM techniques electrodes as structured thin layers on the work piece are used. For the shape controlling of etch form frontside masking design and local backside doping are presented. Influences of the opening size and etch depth on the shape of the etch form is shown. The surface quality of the resulting 3D structures is investigated, with best surface quality (about 1 nm rms) being obtained for electropolishing in 7 wt.% HF at applied current densities of 100 ‑ 300 mA/cm². Application of 3D silicon forms for injection moulding is demonstrated and further implementations of the process for optical and fluidic devices are discussed.