Surface Development during Electroless Copper Deposition

We report on the electroless copper deposition with formaldehyde as the reducing agent. The reaction occurs in high-ly alkaline solutions. Since copper ions are present as EDTA complexes, a catalyst is needed to facilitate copper ion reduc-tion. Methanediolate anions, intermediates of the formaldehyde oxidation, act as such a catalyst. Furthermore, freshly deposited copper exhibits increased catalytic activity toward formaldehyde oxidation. Both effects lead to strong cou-pling between the anodic and cathodic partial processes. Such a feedback can lead to oscillatory behavior of the deposi-tion reaction. In this work we use scanning tunneling microscopy to study the deposition rate with high spatial resolu-tion. We could establish that the deposition rate fluctuates locally and with time. Infroduction Formaldehyde is widely used as the reducing agent in electroless copper deposition. The anodic partial reaction for this process was found to be'