Mechanism study of Ag catalyzed directional etch of silicon for nanowire formation

Abstract

Vertically aligned silicon nanowires (Si NWs) on a wafer-scale single crystalline silicon substrate can be formed by dipping a silicon wafer into an appropriate HF/AgNO3 solution. During the catalyzed etch of silicon in this HF/AgNO3 solution, Ag particles on the bottom of the NWs catalyze the silicon dissolution, and Ag dendrites form and stay on top of the Si NWs. It is not understood why the Ag dendrites in contact with Si NWs do not attack/dissolve the Si NWs. In this paper, we will demonstrate the existence of a protection/passivation layer surrounding the Si NWs by investigating aqua regia or nitric acid cleaning effect. Direct observation using the transmission electron microscope (TEM) also showed the existence of the protection layer. In addition, we found the conductivity of the Si substrate did not have significant impact on the NWs formation rate. The transport of electrons from the bottom of the NWs (where Si dissolves) is identified to be through the hydrogen bubbles. The surface protection model together with the hydrogen transport phenomenon explains the key aspects of the silicon nanowire formation mechanism. ©The Electrochemical Society.