Nucleation of trace copper on the H-Si(111) surface in aqueous fluoride solutions

The initial nucleation process of trace amounts of copper metal on the H-Si(111)(1 x 1) surface in aqueous fluoride solution was investigated by ex-situ scanning tunneling microscopy. We observed that copper nucleates preferentially along step edges and appears to inhibit the step-flow etching of silicon. The presence of copper species in the fluoride solution also appears to inhibit the formation of terrace etch pits, which are known to be initiated by dissolved oxygen. It is suggested that silicon-dihydroxyl-cuprous ion complexes are formed at dihydroxyl kink sites, resulting in the preferential nucleation of Cu metal at step edges and the inhibition of step-flow etching. Copper ions in solution may act as catalysts for the disproportionation and electrocatalytic reduction of superoxide anion radical formed by the electrochemical reduction of dissolved oxygen at the silicon surface. Such reactions would reduce the rate of etch-pit initiation and may also decrease the rate of deposition of metallic copper on the silicon surface.