Canberra Times via Dow Jones Interactive
May  1, 2000

DON'T WRITE OFF SILICON IT'S GETTING LEANER AND MEANER

Simon Grose

  The dynasty of silicon chips might extend its dominance for several
years longer than previous predictions dared to assume.

  A limiting factor in producing increasingly smaller and faster
silicon-based transistors is their silicon dioxide insulating layer. On
today's chips, that insulating layer is an average of about 12 atoms
thick.

  Although most researchers have said that nine to 10 atoms would be the
thinnest reliable insulating layer, Ashraful Alam and his colleagues at
Lu cent Technologies' Bell Labs say thay have shown that the reliability
limit is fewer than six atoms, equal to 1.5 nanometers.

  As a result, they forecast that conventional silicon chip will still
be the main force behind computing until after 2005, instead of the next
couple of years as the other research groups had predicted.

  " Achieving such thin dimensions with the required intrinsic
reliability
was previously thought to be impossible," Alam told delegates at a
recent International Reliability Physics Symposium in San Jose,
California.

  The insulating layer, also known as the gate oxide, is the device's
smallest feature. It lies between the transistor's gate electrode, which
turns current flow on and off, and the channel through which this
current flows. The gate oxide acts as an insulator by protecting the
channel from the gate electrode, preventing a short circuit.

  By reducing continually both the gate oxide thickness and the length
of the gate electrode, the semiconductor industry has doubled the
transistor's switching speed every 18 to 24 months, matching the
progress predicted by the now legendary Moore's Law.

  Because the projected intrinsic lifetime of silicon dioxide as an
insulating layer has been extended, the semiconductor industry will have
more time to develop alternative insulating layers, which will be needed
to continue making transistors smaller and smaller. Alternatively, if
other insulating materials are not found, totally new semiconductor
technologies will be needed.

  " These results will help us direct our process development efforts to
continue advancing integrated-circuit performance for demanding wireless
and networking applications," said Gregg Higashi, a technical manager at
Lucent's Microelectronics Group.

  To obtain their results, the Bell Labs researchers studied first how
thicker gate-oxide layers withstood high voltages over many days, and
developed sophisticated computer models to simulate those results.

  Then they used the same physics-based models to show that a transistor
with a 1.5-nanometer gate oxide operating at 3V for several hours would
be comparable to a similar transistor operating at 1V for 10 years a
very strong reliability indicator.

  Their theoretical work has been confirmed by experimental work on
ultrathin gate oxides, conducted by another Bell team. They used
conventional manufacturing techniques to make ultrathin gate oxides by
growing atomic layers that were exceptionally uniform and smooth.

  Tests of the reliability of the transistors showed that the previous
experimental work on ultrathin oxides had yielded unduly pessimistic
results. www.bell-labs.com.