The linewidth in patterns produced by etching copper layers is more easily maintained using a specific etching medium. In particular, this medium includes aqueous hydrofluoric acid, copper chloride, and an additional chloride salt. The etching medium is also particularly useful for bilayer metal constructions...http://www.google.es/patents/US5620558?utm_source=gb-gplus-sharePatente US5620558 - Etching of copper-containing devices
