Electron Transfer Intermediates in Copper Chemical Machining and Aerobic Regeneration Using Transition Metal Salts

Chemical machining serves essential applications throughout the electronics industry in the manufacture of diverse metallic components. Etchants of transition metal salts are especially favored for their ability to be regenerated by simple oxidizing agents, including atmospheric oxygen, allowing steady-state processing. Despite their relevance, elementary steps in the reaction mechanisms of copper chemical machining have not yet been fully characterized. This review draws from supporting literature to assert hypotheses of intermediate coordination states in the heterogeneous electron transfer mechanism of the surface dissolution reaction by each of three common etchants of transition metal salts: ferric chloride, acidic cupric chloride, and alkaline cupric ammine chloride. Primary evidence is evaluated as well for mechanisms asserted of their aerobic regeneration pathways. Additionally, the reader is directed to relevant mathematical models cited throughout the article, and areas for further research are identified in each section.