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 investigate d by ex-situ scanning tunneling microscopy. We observed that copper nu cleates preferentially along step edges and appears to inhibit the ste p-flow etching of silicon. The presence of copper species in the fluor ide solution also appears to inhibit the formation of terrace etch pit s, which are known to be initiated by dissolved oxygen. It is suggeste d that silicon-dihydroxyl-cuprous ion complexes are formed at dihydrox yl kink sites, resulting in the preferential nucleation of Cu metal at step edges and the inhibition of step-flow etching. Copper ions in so lution may act as catalysts for the disproportionation and electrocata lytic reduction of superoxide anion radical formed by the electrochemi cal reduction of dissolved oxygen at the silicon surface. Such reactio ns would reduce the rate of etch-pit initiation and may also decrease the rate of deposition of metallic copper on the silicon surface.