Electroless copper deposition was performed on submicrometer-trench patterned substrates with a bath containing 8-hydroxy-7-iodo-5-quinoline sulfonic acid (HIQSA) as an accelerating additive and polyethylene glycol (PEG) as an inhibiting additive. Void-free copper filling of trenches was achieved by the addition of both HIQSA and PEG at specific concentrations. Copper deposition rate measurements revealed that HIQSA accelerated the deposition only when it was added together with a very low concentration of PEG. The void-free filling is considered to have resulted from the significant acceleration brought about by HIQSA at the trench bottom, where the concentration of PEG is low.
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