Decrease in acidity was very effective in reducing swirl defects. The occurrence of swirl defects in copper films plated with reduced acid electrolyte was reduced to less than one fifth of that plated with higher acid electrolyte, resulting in the huge decrease in the median defect count to less than one tenth. This reduction can be explained by more uniform plating on seed layers due to the higher resistance of the electrolyte. However, application of pretreatments did not further reduce swirl defects. Inspection on other postplating defects indicated that the major constituents for reduced and higher acid electrolytes were localized protrusions and embedded defects, respectively, and that fewer potential yield-killing defects were generated for reduced acid electrolyte. Analyses on film properties showed the highly Cu(111) texture, fine surface roughness, identical impurity levels, and complete fill of dual-damascene structure for both reduced and higher acid electrolytes. However, a significant degradation of via chain yield was observed for higher acid electrolyte, while no degradation was seen for reduced acid electrolyte. The overall analyses indicated that the use of reduced acid electrolyte led to improved defectivity performance and more reliable film properties compared to that of higher acid electrolyte. (C) 2004 The Electrochemical Society.