Patent ID: 8772174

Claim:
A method of treating silicon to form elongate structures on a treated surface, the method comprising a nucleation step in which metal is deposited on the silicon surface and an etching step in which silicon underlying the deposited metal is etched, wherein a. the nucleation step comprises exposing a silicon containing material to a solution comprising HF at a concentration of less than 5M and 0.002 to 0.2M of metal ions capable of nucleating on and forming a porous layer comprising regions of elemental metal on the silicon surface; and b. the etching step comprises i. exposing the silicon surface comprising regions of elemental metal to a solution comprising HF at a concentration of greater than 5M and 0.001 to 0.70M of an oxidant selected from the group comprising O 2 , O 3 , H 2 O 2 , the acid, ammonium or alkali metal salt of NO 3 − , S 2 O 8 2− , B 4 O 7 2− and ClO 4 − or a mixture thereof; and ii. adding oxidant to the solution during etching to maintain the concentration of oxidant within the above range.