Fabrication of free standing structure using single step electrochemical etching in hydrofluoric acid

This paper presents a new technique of micromachining using single step electrochemical etching in hydrofluoric acid (HF). The electrochemical etching in HF is known as a technique for porous silicon formation. This etching technique is applied to fabricate 3-D structures in single crystal silicon by a combination of anisotropic and isotropic modes. The diameter of the pore, or the width of the trench, can be controlled by the current density. First, vertical walls are formed and after desired depth is obtained, current density is increased by adjusting the light intensity. The width of the trenches is increased under the structures without affecting the width of existing trenches. The connection of the trenches can be achieved and free standing beams obtained with only one mask. The free standing beams with height, width and length of 40 μm, 2 μm and 250 μm, respectively, have been made of single crystal silicon.