Formation of three-dimensional microstructures by electrochemical etching of silicon

This letter describes the promising technique of micromachining using the properties of electrochemical etching of (100)-oriented n-type silicon in a hydrofluoric acid electrolyte. The technique is based on electropolishing of a wafer except for areas where vertical structures are needed and does not require a periodic pattern. Predefined steps of a few microns depth prior to the electrochemical etching define the shape and position of the structures. The three-dimensional microstructure width can be adjusted with the etching parameters, also enabling the formation of free-standing structures. The feasibility of this technique is demonstrated by forming high aspect ratio microneedles and tubes. (C) 2001 American Institute of Physics.