Overview of Device Physics Research
Katsumi Murase
Device Physics Laboratory
Today's high-technology society can be said
to be based on semiconductor devices. Device
physicists and engineers have been pursuing
higher speeds and more sophisticated functions.
This will be the guiding principle for the
development of semiconductor devices for
the foreseeable future. However, when we
think of the limitedness of the earth, environmental
friendliness should also be part of this
guiding principle.
With this in mind, we are carrying out research
for developing innovative electron devices,
such as ultimately-low-energy-consuming single-electron
devices. We are also doing research for controlling
surface atom arrangement on a wafer scale
and creating novel materials, which will
lead to the invention of future devices based
on an entirely new operating principle.
The single-electron device is, as its name
indicates, a device whose operation can be
controlled by a single electron. By employing
single-electron devices for LSIs, we can
reduce the amount of energy consumed to about
1/10,000-1/100,000 that of conventional LSIs.
We succeeded in demonstrating room-temperature
operation of a silicon (Si) single-electron
transistor in 1994. Since then, we have been
making efforts to integrate devices as well
as to create more sophisticated functions
using a simpler device structure. Establishing
nanofabrication technology for Si single-electron
devices has also been one of our main research
targets.
In fiscal year of 1999, we achieved important
and interesting results in four research
areas. The first is a silicon single-electron inverter. The inverter is the most basic element
in logic circuits. Our fabrication of the
first Si single-electron inverter by means
of a novel method called V-PADOX is an important
milestone in the development of single-electron
logic LSIs.
The second achievement is a new type of cross-linked resist for small
pattern roughness. The sidewalls of a lithographically defined
resist pattern have roughness caused by the
molecular structure of resist. This roughness,
while not large enough to affect the characteristics
of conventional devices, must be reduced
for devices that need precise size control
of the order of a nanometer, single-electron
devices for instance. We found that the roughness
can be effectively reduced by cross-linking
polymers of resist.
Thermal oxidation of Si is of central importance
in Si device technology. It has been used
for more than 30 years in the semiconductor
industry. Nevertheless, the microscopic mechanism
of thermal oxidation has remained unclear.
We have created a universal theory for thermal oxidation of
silicon that can describe various aspects of thermal
oxidation quantitatively.
The ultimate processing technology may employ
atom manipulation. For such a technology
to be applicable to device fabrication, however,
artificial atom manipulation should be done
on the whole surface of a wafer. To achieve
atom manipulation, we first need to have
a deep understanding of atom dynamics. The
knowledge of step dynamics observed on ultra-flat Si surfaces will make a key contribution to establishing
a practical atom manipulation technology.
The successful observation of steps resulted
from the combination of our unique surface
modification technique and a specially designed
scanning electron microscope.
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