Universal Theory for Thermal Oxidation of
Silicon
Hiroyuki Kageshima, Kenji Shiraishi, and
Masashi Uematsu
Device Physics Laboratory
When crystal silicon is exposed to oxygen
gas at temperatures around 1000℃, the surface
silicon reacts with the oxygen to become
silicon oxide. Since this phenomenon (silicon
thermal oxidation) has various useful properties,
it plays quite an important role in the fabrication
of semiconductor devices as ULSI chips which
are the heart of today's electronic information
and communication hardware such as cellular
phones, fax machines, electronic communication
switching systems, and personal computers.
In similar reasons, the silicon thermal oxidation
will no doubt play essential roles in the
fabrication of new-generation semiconductor
devices (e. g. silicon single-electron-transistors),
which bear the future highly advanced information
and communication society.
The fabrication of these new-generation devices
inevitably requires atomic control. This
control is also necessary in thermal oxidation,
but is quite difficult to achieve. Observations
on the atomic scale reveal mysterious phenomena
in thermal oxidation, such as "initial
enhanced oxidation" and "pattern
dependent oxidation", which cannot be
explained by the conventional thermal oxidation
theory. We have therefore been studying silicon
thermal oxidation in the atomic world by
solving quantum dynamics (motion law in the
atomic world) with a supercomputer (much
faster than a personal computer).
We found that in silicon thermal oxidation,
in addition to oxygen sinking into the silicon
to form surface oxide, a lot of silicon also
sinks into the surface oxide [1]. This silicon
penetration into the oxide enables us to
explain the "initial enhanced oxidation"
naturally and consistently [2]. Furthermore,
the silicon penetration can be expected to
enable us to predict and control the "pattern
dependent oxidation" with atomical precision,
as well as predict and control the physical
and electrical properties of the formed oxide.
These possibilities are now under assiduous
investigation.
[1] H. Kageshima and K. Shiraishi, Phys.
Rev. Lett. 81 (1998) 5936.
[2] H. Kageshima, K. Shiraishi, and M. Uematsu,
Jpn. J. Appl. Phys. 38 (1999) L971.
Fig. 1. Schematic view of silicon thermal
oxidation and efficiency of our theory.
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