New Virginia Tech technique for polymers
Can lead to improved VLSI performance
A new copolymerization technique developed at Virginia Tech could lead
to improved integrated VLSI chip performance by replacing oxide components
with polymer materials.
The new technique allows the creation of low-dielectric-constant materials
for interconnects in integrated circuits that produce less crosstalk, less
power dissipation, and fewer delays than conventional oxide-based components.
"The industry continues to miniaturize VLSI chips in an effort to
increase the density and speed of the devices- and one of the key limitations
is the interconnection technology," explained Professor
Seshu Desu, director of the Thin Films Laboratory where the new technique
was developed.
"The current standard for interconnects materials are a conductive
metal such as aluminum, and silicon oxide (SiO2) for the dielectric- to
separate the conductors and minimize intercommunication, or crosstalk. Developers
are currently working on switching from aluminum to copper, which will increase
the speed by 30 percent," he continued.
"However, with the metal/SiO2 configuration, the increased speed
and capacity will introduce more crosstalk between the lines, which can
degrade a chip's performance. Moreover, there is power dissipation at the
transistor device level that is proportional to capacitance. Switching to
copper does not improve power loss. It's the dielectric constant of silicon
oxide that is the stumbling block.
"Instead, we developed a method to produce a polymeric material
with a low dielectric constant that reduces delays (thus increasing speed),
while at the same time reduces crosstalk and power dissipation," Desu
said. "With our technique, polymer materials can be made that can serve
as interlevel dielectrics, thus protect against crosstalk and power dissipation."
The difficulty of producing such materials in the past has been that
polymers typically cannot withstand the high temperatures involved in manufacturing
miniature components. "That is one of the advantages of silicon oxide,"
Desu said. "It can withstand, say, 800° C, where most polymers
could only take up to 350-400°."
Desu's team's technique enables polymers to be deposited by chemical
vapor deposition, a preferred method for producing the miniaturized devices,
which can withstand temperatures as high as 500°C. "We can now
make the necessary nanocomposites and hybrids," he said.
"Now we can dial in any dielectric constant and thermal decomposition/stability
temperature and start screening the new materials for optimum properties."
A patent on the process is pending. | 
