Copper etching by water-in-oil microemulsions

The etching of copper was studied using an aqueous chemical etchant dispersed in water-in-oil microemulsions droplets. The aqueous phase consisted of an equimolar copper chloride/potassium chloride solution, a typical copper etchant. The phase behavior, conductivity, copper etching rate, and surface roughness after etching were studied using microemulsions formed with ionic, nonionic, and mixed ionic/nonionic surfactants. The composition of each microemulsion was fixed, and the conductivities and copper etching rate were measured as a function of temperature. The conductivity offers a route to probe ion exchange between microemulsion droplets, while the etching rate is related to the interaction of the droplets with the solid surface. The data show a correlation between etching rate and electrical conductivity of the microemulsion. For a given microemulsion, the etching rate increases as the conductivity increases. Atomic force microscopy showed that the copper surface roughness after etching with the microemulsion was lower than the surface roughness when etched without the microemulsion. The results demonstrate that it is possible to adjust the etching rate and surface roughness by changing the microemulsion composition and temperature. Confinement in water-in-oil microemulsion droplets significantly alters the transport of the etchant to the surface and may find use in nanoscale metal patterning.