Immersion Plating of Copper on Porous Silicon in Various Solutions

The mechanism of immersion plating of copper on porous silicon is studied. Copper metal is deposited on the surface of porous silicon at a rest potential in aqueous solution. It is shown that presence of chloride ions in copper sulfate solution inhibits the metal deposition, whereas the deposition is possible in cuprous chloride solution even though the concentration of chloride ions is high. The behavior is explained in terms of different complexing states of copper ions in each solution. The cathodic reaction is accompanied by the oxidation of silicon as the counter reaction. Immersion plating in nonaqueous organic solution shows that a trace of residual water affects the copper deposition. The difference between metal deposition on porous silicon and a silicon wafer is also discussed.