produces smaller circuits
Technology Research News
Figuring out how to etch ever tinier lines
in silicon chips is only one of the challenges to keeping computer speeds
doubling every 18 months or so. This doubling, described by Moore's Law,
is the main reason computers keep getting more powerful.
Being able to make smaller lines allows manufacturers to etch tinier transistors,
the electrical switches that form the building blocks of computer processors
In order to pack more circuits
into the same area, the metal wires that connect the transistors into
useful circuits also have to shrink. The trick is figuring out how to
efficiently make metal wires 1,000 times narrower than a human hair.
Taking advantage of the same principle that pressure cookers use to speed
dinner preparation, researchers at the University of Massachusetts at
Amherst have made copper and nickel wires narrower than 100 nanometers.
A nanometer is one millionth of a millimeter. In addition to producing
smaller interconnects for computer chips, the technique promises to reduce
the amount of pollution the chipmaking process generates.
The researchers' chemical fluid deposition technique is a hybrid of plating,
which spreads liquid metal over a surface, and chemical vapor deposition,
which coats a surface with a mist of metal atoms, said James J. Watkins,
an associate professor of chemical engineering at the University of Massachusetts.
"We developed a new approach to metal deposition that involves the use
of supercritical fluids as the reaction medium," he said. Like the extra-hot
water in a pressure cooker, supercritical fluids exist under pressure
and at temperatures hotter than those that would turn them into gases
under ordinary pressure.
Supercritical fluids go beyond what is possible in a pressure cooker,
however; they are heated and compressed to the point where they behave
like a cross between a liquid and a gas. "The supercritical fluid has
a density that approaches those of liquids but [has] transport properties
of a gas," said Watkins.
The researchers suspend tiny metal particles in supercritical carbon dioxide.
This makes it possible to apply more metal to a surface than is possible
using metal vapor and apply it faster and more consistently than using
liquid metal, according to Watkins.
The researchers made electrically conductive wires by filling tiny trenches
carved into silicon chips with particles of copper or nickel suspended
in the supercritical carbon dioxide. The trenches can be narrower than
100 nanometers, which is too small to fill using ordinary liquid or vapor
techniques, said Watkins.
Chemical fluid deposition also sidesteps both the hazardous emissions
produced by chemical vapor deposition and the water baths used in metal
plating processes that result in contaminated wastewater, according to
The researchers are doing "outstanding" work in supercritical fluid chemical
deposition, said Gregory L. Griffin, a chemical engineering professor
at Louisiana State University. They will probably have to demonstrate
higher growth rate or a similar advantage before the technique will be
adopted, however, he said. "Previous groups, including one commercial
vendor, have shown similar trench-filling ability using conventional chemical
Chemical fluid deposition could be used in practical applications in two
to three years, said Watkins. The main challenge is adapting the other
materials and equipment used to manufacture the chips so they can handle
the high pressure needed to make supercritical fluids. "The technique
can be adapted [for manufacturing] in a straightforward manner. The problem
of handling wafers in a high-pressure environment is presently being addressed
by a number of manufacturers," he said.
Watkins' research colleagues were Jason M. Blackburn, David P. Long and
Albertina Cabanas of the University of Massachusetts. They published the
research in the October 5, 2001 issue of the journal Science. The research
was funded by the National Science Foundation (NSF), the David and Lucile
Packard Foundation and Novellus Systems, Inc.
Timeline: 2-3 years
Funding: Corporate; Government; Private
TRN Categories: Materials Science and Engineering; Integrated
Story Type: News
Related Elements: Technical paper, "Deposition of Conformal
Copper and Nickel Films from Supercritical Carbon Dioxide," Science (online),
September 13, 2001
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