The Decomposition of the Sulfonate Additive Sulfopropyl Sulfonate in Acid Copper Electroplating Chemistries

The decomposition of sulfopropyl sulfonate (SPS, 4,5-dithiaoctane-1,8-disulfonic acid) in acid copper electroplating chemistries was studied using scanning electrochemical microscopy (SECM), UV-visible spectroscopy, high pressure liquid chromatography, liquid chromatography mass spectrometry, and electron spin resonance. The primary decomposition product is proposed to be the thiolsulfonate of SPS. Although this oxidation product can be formed by reaction with hydrogen peroxide, SECM studies of oxygen reduction on copper showed that there is not a peroxide intermediate and the product of oxygen reduction on copper in dilute sulfuric acid is water. The data suggests that SPS stabilizes Cu(I) and this complex is the intermediate. For this scheme, oxygen reacts with the SPS/Cu(I) complex in solution to form the thiolsulfonate of SPS and Cu(II). © 2003 The Electrochemical Society. All rights reserved.