Selective Wet Etching of Microcontact-Printed Au and Ag Substrates Using Fe3+ and Thiourea
Original Publication Date: 2003-Jun-10
Included in the Prior Art Database: 2003-Jun-10
Disclosed is an etch bath for fabricating thin Au and Ag patterns by using microcontact printing (5CP) and selective wet etching. Specifically, the etch system is an acidic aqueous solution of Fe3+ and thiourea.
Selective Wet Etching of Microcontact -Printed Au and Ag Substrates Using Fe 3+ and Thiourea
Microcontact printing is a soft-lithographic technique that employs a micropatterned elastomeric stamp that is inked, dried, and placed on a substrate to apply a reactant in the regions of contact . This technique is the method of choice to pattern self-assembled monolayers (SAMs) of alkanethiolates on noble metals, including Au, Ag, Cu and Pd. Patterned SAMs alter the wetting, transport and adhesion properties of a substrate locally, and find interesting applications as resists, for example, to protect a substrate selectively in a wet-etch process . The use of SAMs as high-contrast barriers is challenging, however, because these layers are ultra-thin (1-3 nm only) and have defects. An alkaline solution -with dissolved CN and O2 can be used to etch thin Au and Ag substrates, but this bath shows limited selectivity when printed SAMs are the resist. Increased selectivity can be achieved, for example, by having additives in the bath that can heal defects in the SAM, or by employing large etchants that cannot diffuse through defects in the printed monolayer
. Despite having such advanced etch strategies, thin layers of Au and Ag (~100 nm in 3+thickness) can be etched with good selectivity when using an aqueous solution of Fe and thiourea as the etch system. It is not obvious that this system provides high selectivity, but a bath containing these compounds can be oper...