Metal-assisted electrochemical etching of silicon.

In this paper the metal-assisted electrochemical etching of silicon is introduced. By electrochemical measurement and sequent simulation, it is revealed that the potential of the valence band maximum at the silicon/metal interface is more negative than that of the silicon/electrolyte interface. Accordingly, holes injected from the back contact are driven preferentially to the silicon/metal interface. Consequently, silicon below metal is electrochemically etched much faster than a naked silicon surface without metal coverage. Metals such as Ag and Cu have been utilized to catalyze the electrochemical etching. Feature sizes as small as 30 nm can be achieved by metal-assisted electrochemical etching. Meanwhile, the metal-assisted electrochemical etching method enables convenient control over the etching direction of non-(100) substrates, and facilitates the fabrication of orientation-modulated silicon nanostructures.