As semiconductor processes head below 65 nm, scientists are scrambling to
find a light source that
will let fabs manufacture
next-generation chips.
Martin Richardson, an optics professor
and director of the University of Central
Florida's laser plasma laboratory, believes
extreme-ultraviolet (EUV) light could
replace the deep-ultraviolet lithography
that's currently used to carve circuit patterns onto silicon wafers.
"We must use a light source with a
wavelength that's short enough to allow
the minimum feature size on a chip to
go down to possibly as low as 12 nm,"
Richardson says. "The switch to EUV
will be the largest technology transition
that the computer chip industry will
ever make."
UCF's EUV technology directs a laser at
liquid microdroplets containing a small
amount of tin (). The laser
then heats the target, creating a plasma
that radiates light (invisible to the human
eye) at 13.5 nm. The light travels into a
condenser, which collects and directs it
onto a mask that serves as a circuit pattern stencil. Finally, the mask's pattern is reflected onto a series of curved mirrors,
which reduces the image's size and focuses it onto a silicon wafer.
Yet a real-world EUV source powerful
enough to drive chip steppers—the
devices chip manufacturers use to
place detailed circuitry images onto
wafers—has proven elusive. The argon-fluoride excimer lasers that manufacturers currently use for conventional UV
chip lithography simply aren't up to the
task for EUV, Richardson says. "There
are no strong laser sources at 13.5 nm,"
he notes.
Richardson and his team turned to
Crawley, England-based Powerlase and
its diode-pumped solid-state (DPSS) Starlase laser. "It is one of the highest-powered, pulsed solid-state lasers on the
market today," says Richardson. The
researchers combined the laser with
their own tin-doped micro-droplet laser
plasma source technology to create an
EUV light source that Richardson claims
is 30 times more powerful than any previously reported system.
The UCF technology also effectively
eliminates the neutral and charged particles emitted by existing EUV plasma
sources, Richardson says. If allowed to stream freely away from the source, the
particles can harm the expensive optics
used in EUV steppers. "This affects the
stepper's performance and operational
life," Richardson says.
Richardson believes his technology is
poised to play a crucial role in EUV-based
chip manufacturing. All three major stepper manufacturers—ASML, Canon, and
Nikon—have EUV development programs
in place and have already developed
alpha stepper prototypes, Richardson
says. Sematech, the non-profit semiconductor research consortium, forecasts
that EUV production will begin at the 45nm level in 2009.
Richardson, however, believes that full-scale EUV manufacturing isn't likely to
start in a meaningful way before 2011 or
2012. "Whenever it begins, EUV will be
the next generation of computer chip
manufacturing," he says. "All that's needed now is a light source, and ours has the
required parameters."
