Band model for explaining new effects observed in electromechanical micromachining of Si

An energy band diagram model has been utilized to characterize the electrochemical behavior of Si. A new passivation phenomenon is presented and the underlying mechanisms of this new passivation effect are analyzed with the aid of the energy band diagram representation of the Si/KOH interface. The new effect consists in the fact that, in the presence of a pn-junction at the Si/KOH interface, the p-type substrate does not etch even when it is under open circuit conditions, although one would normally expect that both sides of the junction would be etched away. An explanation of this new passivation effect is based on an inversion layer formation at the p-type surface. It is concluded that a detailed understanding of the etching/passivation mechanisms outlined enables processes to be designed with selective etching of any desired layer, particularly including low resistivities. This, in turn, makes possible the simultaneous production of optimized active devices in retained layers. An example of what can be achieved with the electrochemical passivation technique is shown consisting of a passivated n-type bridge over a cavity etched from a p-type substrate