Gentle Lithography

Lithography is the key process in microchip fabrication whereby circuit elements are built up or "written" onto a backing in a series of steps that can include chemical action, heating, and irradiation. Many attempts are underway both to devise simpler forms of lithography and to produce smaller circuit elements. The use of scanning tunneling microscope (STM) probes to fashion small structures by moving individual atoms or molecules is one way to do this, albeit at a very slow rate.

One new step in this direction is provided by Peter Kruse and Robert Wolkow (National Research Council, Ottawa), who report a "gentle lithography," one requiring no heating, etching, or exposure to photons, in which a silicon surface is covered by a monolayer of benzene molecules. Thereafter the benzene can be selectively removed in long strips (as if a combine were harvesting grain), with an STM probe, to produce deliberate patterns with spatial resolutions as small as 2 nm. Then another species of molecule, such as ethylene, can be laid down in the cleared areas. According to the researchers, patterned ethylene (after it's been heat treated) could lead to the creation of silicon carbide structures. (Kruse and Wolkow, Applied Physics Letters, 2 December 2002.)