Highly ordered hexagonally arranged sub-200 nm diameter vertical cylindrical pores on p-type Si using non-lithographic pre-patterning of the Si substrate



Anodically etched two-dimensional (2-D) arrays of highly ordered sub-200 nm in diameter vertical cylindrical pores were fabricated on p-type Si wafers, with a resistivity of 6–8 Ω cm, by non-lithographic pre-patterning of the silicon substrate through a self-assembled porous anodic alumina (PAA) thin film, directly grown on the Si wafer. The PAA film was grown by electrochemical oxidation of a thin Al film in an oxalic acid aqueous solution electrolyte. Through the PAA pores, concave etch pits were formed on Si by chemical etching, that were then used as pore initiation sites for electrochemical macroporous silicon formation. The so formed vertical cylindrical pore arrays showed perfect hexagonal arrangement on the Si surface. A pore diameter down to 180 nm and a pore height up to ∼1 μm were achieved for the first time on p-type Si. The developed technology is particularly interesting for photonic crystals and sensors applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)