Using Micromachining, Molecular Self-Assembly, and Wet Etching to Fabricate 0.1-1-.mu.m-scale structures of Gold and Silicon

In this paper, we report a procedure that combines micromachining,l molecular self-assembly, and wet etching and provides the basis for a method to fabricate 0.1-1pm-scale structures of gold supported on glass or silicon. This procedure has four steps: (i) formation of a monolayer of the thiolate2 IHO(CHilzS] from B-mercaptoethanol IHO(CH2)2SH] on the surface of a film of gold; (ii) generation, by micromachining, of 0. l-l-pm-scale regions of bare gold in the monolayer of HO(CHdzS; (iii) selfassembly of a monolayer of CHa(CHdrsS on micromachined regions of bare gold;3 (iv) selective etching of gold film underlying HO(CH2)zS by using an aqueous solution of cyanide ions (CN-) saturated with Oz. Areas of gold film supporting self-assembled monolayers (SAMs) of CHs(CHz)rsS are protected from etchinga and form microstructures of gold with lateral dimensions as small as 0.1 pm and vertical dimensions as small as 25 nm.5 Because gold is a good electrical conductor and does not oxidize in air, it is frequently used in the fabrication of small structures. Microstructures of gold are used as microelectrodes,o small conductors for dense microelectronic devices,T scatterers and absorbers for ion projection lithography and etching,T'8 and masks for X-ray lithography.T'e Here we report a simple, wet chemical procedure for fabricating 0.1-1-pm-scale structures of gold. In