Growth spurt: New wafer facility to open
o create today’s most
advanced semiconductor lasers and microelectronic devices, researchers
use specialized equipment to deposit layer upon layer of different materials
atop the glassy surface of a semiconductor wafer. Now, a new facility
housed in the Engineering Centers Building promises to make this meticulous
enterprise much more efficient, accurate and reliable.
Slated for completion early next year, the new resource
is known as the “multi-wafer” growth facility because its
state-of-the-art machines can process up to three wafers simultaneously.
The department’s old system, in contrast, handled only one wafer
at a time.
The added efficiency and sophistication will greatly
aid any scientific investigations that involve producing complex, multi-layer
structures, says Professor Luke
Mawst, who spearheaded the effort to build the facility together
with Philip Dunham Reed Professor Dan
Botez. For example, Mawst’s and Botez’s research can
require structures containing up to 500 layers and films as thin as
one nanometer, or one-billionth of a meter.
“This facility gives us an edge over a lot of
other universities,” says Mawst. “For projects such as ours,
whoever has the best materials and the ability to make the structures
can really get ahead of the game and develop devices first.” Botez
and Mawst are working to create mid-infrared semiconductor lasers that
emit at very long wavelengths, which show enormous potential for detecting
chemical agents and diagnosing disease non-invasively.
Others in the department, including Professors Robert
Blick, Zhenqiang
(Jack) Ma and Dan
van der Weide, will use the facility to grow high-quality microelectronic
devices on wafers. One example are tiny devices known as heterojunction
bipolar transistors, with applications to cellular phones, fiber-optic
telecommunications, and other technology.
The core of the new facility’s system is a stainless
steel reaction chamber with room for three two-inch wafers; Mawst calls
it a scaled-down version of a commercial production system, which typically
houses six to seven. Within a sealed environment, wafers of the semiconductor
gallium arsenide are placed in the chamber and heated to high temperatures.
Next, gases containing elements such as phosphorus, gallium and arsenic
are introduced into the chamber, their amounts and residence times closely
controlled by computer.
By varying the gas-phase composition in the chamber,
researchers can precisely dictate the thicknesses and compositions of
different layers deposited on the wafers to build very complex structures,
says Mawst. The new system will also include a suite of tools for monitoring
certain characteristics during growth, such as wafer temperature and
reflectivity. The latter indicates whether the wafer surface has remained
smooth during processing or if defects have developed.
Financial support to build the facility came from
several sources, including funds from the Wisconsin Alumni Research
Foundation (WARF) administered through the UW-Madison Graduate School;
a grant from the Department of Defense; and the College of Engineering.
