Fabrication of mechanical structures in p-type silicon using electrochemical etching

In this paper, free standing beams and trench structures are successfully fabricated in p-type silicon using electrochemical etching in HF-dimethyl-formamide (DMF). The morphology of the etched surface and the etch rate as a function of the current density are investigated. The optimization of the current density enables to fabricate trench structures with width and pitch of 2.5 mu m and 4 mu m, respectively. After the fabrication of these trench structures, the applied voltage is increased in order to connect these trenches under the wall structures. Therefore free standing beams with single crystal silicon can be achieved in one step. The aluminium etch rate in 4% HF-DMF is very low due to low water content in this chemical solution. Furthermore silicon dioxide is not attacked by the etchant during the electrochemical etching. Therefore thermal dioxide layer can be used as a masking layer to make an initial pit. This makes the electrochemical etching process simple. However, it is difficult to control the etched width using the current density adjusted by the applied voltage during the etching. (C) 2000 Elsevier Science S.A. All rights reserved.