New phenomena observed in electrochemical micromachining of silicon

The authors report on electrochemical micromachining experiments, including a new passivation phenomenon and several phenomena observed in I-V characteristics of Si in KOH. I-V measurements were used to reveal the underlying mechanisms of etching and passivation. The physical basis of these processes and secondary effects such as illumination dependency of the reactions at the Si/KOH interface are investigated using the energy band diagram representation of the interface. Based on the results of these experiments, an electrochemical micromachining technique has been developed, making possible the production of structures with a very high aspect ratio. This technique is fully compatible with a standard CMOS process. The new passivation phenomenon allows n-regions to be etched away while the p-type surface is passivated due to an n-type inversion layer formation. This considerably extends the process flexibility of the conventional electrochemical micromachining technique by making it possible to etch either p- or n-regions as required.<>