Selective growth of metals on semiconductors has recently raised considerable interest due to its possible application in the direct formation of conduction paths and contacts on semiconductors. We produced small structures by photoexcited electroless plating of Cu on p-type Si(001). The p-type substrate forms a Schottky barrier with the solution which inhibits the plating process. Local illumination creates minority carriers which become available to discharge metal ions. Illumination was done by converging a 1-5 mW laser beam to a 1-2 mum focus diameter on the substrate in the plating solution using an optical microscope. The dimensions of the dots are determined by the diffusion length of the excited minority carriers. We analyzed the diameter of the growing dots as a function of the laser light wavelength and intensity, illumination duration, composition of the solution and charge carrier lifetime in the substrate. The lateral dimensions of the structures produced are found to decrease with reduced laser wavelength or intensity but are independent of the duration of illumination. Shorter minority carrier lifetimes in the semiconductor substrate lead to a further reduction of structure dimensions. The effect of spontaneous background precipitation on the Si surface is studied as a function of the solution composition. The optical reflectivity can be related to the fractal surface roughness. (C) 2004 American Vacuum Society.