A selective etching solution for use with patterned self-assembled monolayers of alkanethiolates on gold

This paper describes a selective etching solution for use with patterned self-assembled monolayers (SAMs) of alkanethiolates on the surface of gold; it is also effective for SAMs on the surfaces of silver and copper. This etching solution uses thiosulfate as the ligand that coordinates to the metal ions and ferricyanide as the oxidant. This etchant has a number of advantages relative to the system of cyanide ion in oxygen-saturated, alkaline water used in previous work. First, it is less toxic, less hazardous, and has smaller environmental impact. Second, using it, complete etching of bare gold can be achieved more rapidly (similar to 8 min versus similar to 15 min for 200 Angstrom of Au). Third, etching of bare gold occurs with fewer defects in the SAM-covered regions and generates features of gold with higher edge resolution. The influence of the composition of the etching solution on the rate of etching was studied systematically.