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Scanning Tunneling Microscopy of Superfilling in FormulaContaining Chloride, Polyethylene Glycol andBis-3-Sodiumsulfopropyl-Disulfide

By Yunlin Fu, Sihzih Chen, Shuehlin Yau, Wei-Ping Dow and Yuh-Lang Lee


In situ scanning tunneling microscopy (STM) was used to study copper deposition at vacancy defects on a copper thin film underpotentiostatic conditions at −0.20 V (vs. Ag/AgCl) in a formula containing sulfuric acid, chloride, polyethylene glycol (PEG), andbis-3-sodiumsulfopropyl-disulfide (SPS) – the widely used mixture to facilitate Cu superfilling at recessed features in semiconductorprocessing. The vacancy island measuring ∼70 nm wide and 12 nm deep sat in the middle of a facetted surface structure at thebeginning. Cu deposit nucleated mainly at the rim of the vacancy and grew into stacked Cu(111) facets. These local pyramidal Custacks could restructure into wider Cu(111) terraces by transferring Cu atoms rapidly from higher to lower planes. Voltammetricresults showed that Cu deposition was suppressed in a plating bath containing 1 mM KCl + 88 μM PEG8000 + 10−7 M SPS.Steps with sharp edges bunched in the course of Cu deposition. The vacancy island was filled with Cu deposit assuming smoothterraces with sharp step edges aligned mainly in the 121 directions of the Pt(111) electrode, suggesting crystalline packing in theCu deposit. Atomic-resolution STM imaging revealed a hexagonal array presumed to be the (√3 × √3)R30◦ – Cl− adlattice

Year: 2014
DOI identifier: 10.1149/2.049312jes
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