Two-Dimensionally Grown Periodic Pores Formed by Anodization of p-Type Silicon in Concentrated NH₄F Aqueous Solution: A Platform for Maskless Patterning of Metals by Electrodeposition

Abstract

Self-organization is a fascinating topic in electrochemical processing because sophisticated structures are easily fabricated. Although the formation of many self-organized morphologies has been reported in the cathodic electrodeposition of metals and alloys, almost all the structures obtained via anodization were cylindrical pores grown perpendicular to the surface. Thus, a bottleneck exists for the production of microstructures laterally grown on substrates. Among self-organized structures grown via anodization, two-dimensional patterns formed during the anodization of Si in a concentrated NH4F aqueous solution are rare examples because two-dimensional pore growth occurs in this system. Here, we investigate the two-dimensional pattern formation on Si in the anodization and propose a mechanism for the pattern formation process. Our results suggest that SiF x species should exist stably in the highly concentrated NH4F aqueous solution and likely play a key role in the two-dimensional pattern formation. By controlling the reactivities of SiO2 and SiF x , we demonstrate that the electrodeposition of Au occurs selectively not on the original Si surface but within the two-dimensional pores.