Additive-assisted nucleation and growth by electrodeposition: I. Experimental studies with copper seed arrays on gold films

Nucleation and growth in the presence of additives during Cu electrodeposition on ordered arrays of Cu seed clusters on a polycrystalline Au film were investigated. The seed clusters, formed by an E-beam lithography method, were 25 nm in diameter and positioned in square arrays (100, 200, or 300 nm spacing) with overall dimensions of 20 × 20 μm. Electrodeposition was carried out in acid sulfate solutions (0.6 M CuSO₄ and 1.0 M H₂ SO₄) containing various concentrations of additives [0.1-10 ppm Cl-, 3-3000 ppm poly(ethylene glycol), and 3-50 ppm bis(3-sulfopropyl) disulfide]. Image analysis methods were used to extract quantitative information on the effect of additives, array spacing, and potential on the probability of finding Cu nuclei at a given distance from a Cu seed cluster as well as finding the nearest neighbor to any deposited Cu nucleus. The level of chloride concentration was found to mediate the extent of seed growth vs wild nucleation. Low levels of chloride (0.1 ppm) yielded growth predominantly at the Cu seeds with virtually no wild nuclei. Progressively higher levels of chloride (1 and 10 ppm) yielded lower deposition rates at the Cu seeds and proportionally higher levels of wild nucleation. Experimental results are compared with numerical simulations in Part II [Stephens, J. Electrochem. Soc., 156, D385 (2009)].