Superfilling Evolution in Cu Electrodeposition

Interesting phenomena were observed during an investigation on the accelerating effects of 3-mercapto-1-propane sulfonic acid ~MPSA!, i.e., different aging times of MPSA result in different filling profiles. When MPSA was added to the electrolyte before electrodeposition, subconformal deposits appeared, whereas MPSA aged over 12 h enabled superfilling. From -visible analysis, over 99% MPSA was converted to bis~3-sulfopropyl!disulfide ~SPS! within 12 h through the reaction with 21, which means that SPS was, in terms of visible superfilling, the real accelerator. This arose from the fact that SPS adsorption first, while MPSA underwent Cu21 reduction first at the trench entrance.