Gold etching for microfabrication

The etching of gold is a key enabling technology in the fabrication of many microdevices and is widely used in the electronic, optoelectronic and microelectromechanical systems (MEMS) industries. In this review, we examine some of the available methods for patterning gold thin films using dry and wet etching techniques. Dry methods which utilise reactive ion etching (RIE) have a number of important advantages over other methods, but the low volatility of gold etch products has made the development of suitable processes problematic. More recently, the adoption of high-density plasma reactors with optimised chlorine-based chemistries has allowed improved processes to be developed, and etching in hydrogen plasmas also shows promise. Wet etching methods for gold have also been critically reviewed. Traditionally, iodine- and cyanide-based etch processes have been used, but in the last decade, a number of alternative etchants have been studied. Of particular interest is the recent development of a range of novel non-aqueous-based gold etchants, and the suitability of these etchants for microfabrication is assessed.