ＥＤＴＡ浴による高速度無電解銅めっきの反応機構

Abstract

Mechanisms of high-speed electroless copper deposition from EDTA bath were investigated by means of analytical method, X-ray diffraction and electrochemical method. From the analysis of bath components and the reaction products such as copper and hydrogen gas during the electroless copper deposition at 70°C, it was confirmed that the following reactions were occurring in the bath.Cu deposition reaction: Cu(II)-EDTA+2HCHO+4OH-→Cu+2HCOO-+H2+2H2O+EDTA…(1)Cannizzaro reaction: 2HCHO+OH-→CH3OH+HCOO- …(2)The reaction (2) was remarkably promoted by the increase of bath temperature above 60°C and pH higher than 12.5. X-ray diffraction data of the powdery deposits which have been obtained by 1 hour mixing of CuO and Cu2O powders with the Cu-EDTA bath at 60°C showed that the reducing power of the solution containing both formaldehyde and EDTA was higher than that of the solution containing each component separately. In the former case, the added Cu2O was completely reduced to metallic copper. This fact suggests that the spontaneous decomposition of the EDTA bath does not occur through the formation of Cu2O contrary to the case of Rochelle salt bath, but spontaneous decomposition starts in the bath either by copper particles removed from the surface or by the reduction of metallic copper when the reducing power of the solution increases. The mixed potential theory of the reaction (1) was also studied by potential sweep method.