Microcontact Printing of Alkanethiols on Silver and Its Application in Microfabrication

Abstract

This paper describes the use of microcontact printing (μCP) to generate patterned self‐assembled monolayers (SAMs) of alkanethiolates on the surfaces of evaporated films of silver. Using patterned SAMs of alkanethiolates as nanometer‐thick resists, patterned microfeatures of silver with sizes down to ∼200 nm were fabricated on by selective etching in aqueous solutions containing , and . Complete etching of silver can be achieved more rapidly than that of gold: ∼20 s vs. ∼20 min for 50 nm thick metal films when similar ferricyanide etchants were used. Microstructures of silver produced by the present method have higher edge resolution (typically, ∼20 nm vs. ∼100 nm) and far fewer defects (∼10 pits/mm2 vs. ∼103 pits/mm2) than those of gold fabricated by a similar procedure. Silver lines (0.2 μm in thickness, ∼50 μm in width, and ∼5 mm in length) had the expected metallic conductivity (≈5.56 × 105 S/cm); parallel lines of silver (0.2 μm in thickness, ∼10 μm in width, ∼1 mm in length, and separated by ∼10 μm) were electrically isolated from each other. Aqueous solutions containing other coordinating ligands and oxidants, , and , were also selective etchants for use with patterned SAMs of alkanethiolates on silver. Patterned structures of silver (50 nm thick) on could be used as secondary masks for etching of in aqueous solutions of , and of Si(100) in aqueous solutions of KOH and i‐propanol. Patterned films of silver (0.2 μm thick) on silicon wafers could be used as masters to cast elastomeric stamps with surface relief to be used for μCP. By choosing appropriate etching conditions, microparticles of MX (M = Ag; X = Cl, Br, I, OH, and SCN) could be formed in situ on the underivatized regions of the SAM‐patterned surface during etching of silver.