 CHAMPAIGN,
Ill. — Creating high-resolution metallic interconnects is an essential
part of the fabrication of microchips and other nanoscale devices. Researchers
at the University of Illinois at Urbana-Champaign have developed a simple
and robust electrochemical process for the direct patterning of metallic
interconnects and other nanostructures.
“Solid-state superionic stamping
offers a new approach, both as a stand-alone process and as a complement
to other nanofabrication techniques, for creating chemical sensors, photonic
structures and electrical interconnects,” said Nicholas X. Fang, a professor
of mechanical science and engineering, and corresponding author of a paper
published in the Feb. 14 issue of the journal Nano Letters.
The S4 process uses a patterned superionic
material as a stamp, and etches a metallic film by an electrochemical reaction.
In superionic materials, metal ions can move almost freely around the crystal
lattice. These mobile materials can also be used in batteries and fuel
cells.
Unlike conventional processing –
in which patterns are first placed on photoresist, followed by metal deposition
and subsequent etching – the S4 process creates high-resolution metallic
nanopatterns in a single step, potentially reducing manufacturing costs
and increasing yields.
The S4 process begins by carving
the desired pattern into a stamp made of superionic material, such as silver
sulfide, using focused ion beam milling. The stamp is then placed on the
substrate and a voltage is applied. This produces an electrochemical reaction
at the contact points of the interface.
The reaction generates metal ions,
which migrate across the interface into the stamp. As the reaction continues,
the stamp progresses into the substrate, generating features complementary
to the pattern on the stamp.
“The stamp acts like a sponge, soaking
up metal ions,” said Fang, who also is a researcher at the university’s
Beckman Institute for Advanced Science and Technology, and at the Center
for Nanoscale Chemical-Electrical-Mechanical Manufacturing Systems.
“The most difficult step in the S4
process is making the stamp extremely flat and smooth,” said graduate student
Keng H. Hsu, the paper’s lead author. “Currently, our resolution for patterning
details is 50 nanometers. As better tools for engraving the stamps are
developed, we will achieve finer resolution.”
Ultimately, the resolution will be
limited by the mechanical properties of the stamp, Hsu said.
With Fang and Hsu, co-authors of
the paper are Placid M. Ferreira, a U. of I. professor of mechanical science
and engineering, and director of NanoCEMMS; and graduate student Peter
L. Schultz.
The work was funded by the U.S. Department
of Energy and the National Science Foundation.
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