Copper hydride formation in the electroless copper plating process: in situ X-ray diffraction evidence and electrochemical study

Copper hydride, CuH, has been shown by in situ X-ray diffraction method to form in the process of electroless copper deposition in alkaline solutions containing Cu II complexes with tartrate and ammonia and borohydride, BH 4 −, as a reducing agent. The rate of possible chemical and electrochemical steps was measured and compared with the rate of autocatalytic Cu II reduction process. Results indicate the existence of two process routes: (1) coupling of simultaneous electrochemical reactions of BH 4 − oxidation and Cu II reduction with the enhancement of cathodic reaction due to H 2 evolution in anodic reaction, (2) electrochemical steps of Cu II reduction to Cu I and consecutive chemical steps of CuH formation and decomposition. The route including CuH intermediate gives a lower Cu deposition rate.