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.)