Cyanide- and thiourea-free electrochemical etching of gold for microelectronics applications

Electrochemical etching of gold using chemical species other than cyanide and thiourea has been investigated. Through complexation with gold ions, chemical species such as chloride and iodide are able to facilitate electrochemical oxidation of gold. It was found that while chloride makes electrochemical oxidation of gold feasible, particularly at highly acidic conditions, the process appeared inadequate for applications in microelectronics as it left microscopic gold residues on areas where gold seed layers were to be removed, most probably due to the limited complexation ability of chloride with gold ions. In contrast, electrochemical etching of gold using iodide resulted in complete removal of gold seed layers. To prevent electrochemical and chemical oxidation of iodide, we envisioned the use of sacrificial stabilizers that are oxidizable at anodic potentials, at which gold is oxidized in the presence of iodide, and are able to convert the generated iodine, if there is any, back to iodide. With the use of such a sacrificial stabilizer, sulfite, we demonstrated that electrochemical etching of gold using iodide is suitable for gold-seed-layer removal in microelectronics applications. The potential and merits of electrochemical etching of gold using other complexing agents such as thiocyanate and bromide are also discussed. (c) 2007 The Electrochemical Society.