Electroless etching of Si with IO(3)(–) and related species

We have previously derived seven requirements for the formulation of effective stain etchants and have demonstrated that Fe(3+), Ce(4+), and VO(2)(+) + HF solutions are highly effective at producing nanocrystalline porous silicon. Here, we show that Cl(2), Br(2), I(2), ClO(3)(–), BrO(3)(–), IO(3)(–), I(–), and I(3)(–) induce etching of silicon when added to HF. However, using the strict definition that a pore is deeper than it is wide, we observe little evidence for porous layers of significant thickness but facile formation of pits. Iodate solutions are extremely reactive, and by the combined effects of IO(3)(–), I(3)(–), I(2), and I(–), these etchants roughen and restructure the substrate to form a variety of structures including (circular, rectangular, or triangular) pits, pyramids, or combinations of pits and pyramids without leaving a porous silicon layer of significant thickness.