Pattern transfer: Self-assembled monolayers as ultrathin resists

Abstract

This review includes three sections: (i) preparation, structure, and properties of self-assembled monolayers (SAMs); (ii) techniques for patterning SAMs, including microcontact printing (μCP), UV-photolithography, and e-beam writing; and (iii) use of patterned SAMs as ultrathin resists (2–3 nm thick) in processes for pattern transfer based on selective chemical etching and selective deposition. Microcontact printing is a non-lithographic technique for forming patterned features with dimensions ≧100 nm; the initial product of patterning is organized monolayers of alkanethiolates on Au, Ag, Cu and GaAs, and of alkylsiloxanes on Si/SiO 2 and glass. In this technique, an elastomeric stamp having a surface patterned with a relief structure is used to generate patterned SAMs on the surfaces of solid materials. These patterned SAMs are resists that protect the underlying substrates from dissolution in selective etchants (for example, for evaporated thin films of Au and Ag, aqueous solutions of K 2S 2O 3, K 3Fe(CN) 6 and K 4Fe(CN) 6). Patterned structures of gold or silver that are produced by the combination of μCP and selective etching can be used as the secondary masks for subsequent processes such as isotropic etching of SiO 2, isotropic or anisotropic etching of Si, anisotropic etching of GaAs, and reactive ion etching (RIE) of Si. Patterned SAMs can also be used as templates for selective deposition of metals by chemical vapor deposition (CVD), electroplating, or electroless deposition.