Scientific Understanding Needed for 0.1-Micron Chip Process
nikkeibp.asiabiztech.com
The chip industry is moving toward a minimum design size of 0.1 micron, down
from 0.13 micron the most advanced today. For the coming years, the chip
industry has to be ready to design with 0.1 micron process. Tadahiro Ohmi,
Professor of Advanced Science and Technology of Information and
Microelectronics at the Tohoku University of Japan gave a presentation at
Industry Strategy Symposium (ISS) 2000 held recently in Tokyo, saying that
chip design under a 0.1 micron rule should be established with perfectly
scientific manufacturing to achieve profitable chip manufacturing with small
production of, e.g. 2,000 to 3,000 wafers per month.
Professor Ohmi, who is dubbed "Dr Ultra-Clean Scientist," has been making
efforts to establish the perfect cleanroom and process equipment systems for
advanced semiconductor chip industry. He proposed several ideas to achieve
a success in the coming age.
Plasma Equivalent Circuit, a Key
First, plasma process equipment should be eliminated with variation among
equipment systems. To do this he proposed to make the same radio frequency
(RF) equivalent circuit for every plasma chambers. A plasma phenomenon is
described with the RC (R: resistance, C: capacitance) equivalent circuit. An
equivalent circuit of a plasma chamber roughly consists of plasma capacitance
CP and resistance RP, and a stray capacitance CCW between cathode and
chamber wall. In conventional chambers, CCW is much larger than CP,
leading to flowing out of RF plasma current. This CCW strongly depends on
individual chambers and therefore, a design to reduce the CCW is required. In
addition to this capacitance, other stray capacitances, resistances and
inductances should also be reduced as small as possible.
With this new design architecture, RF plasma is effectively confined between a
cathode and a wafer on a suscepter, resulting in higher efficiency or higher
process speed, as well as less variation among plasma systems. In an example
of a plasma chemical vapor deposition (CVD), the reduction of CCW to 1/4
and other resistances and inductance to 1/100 to 1/2 results in 5.5 times
deposition speed and a double breakdown voltage of the film. The plasma
excitation efficiency is over 80%, compared with 5% or less in conventional
systems.
Scalability, Functions, Smaller
Second, process scalability should be considered into the equipment design.
With a certain wafer size, the equipment should be available in 0.25 micron
process and 0.05 micron process.
Third, a single chamber should be available in both deposition and etch. This is
because the chip-manufacturing business would be profitable even with small
lots of wafers.
Fourth, vertical cluster tools should be essential to reduce a footprint area of a
tool system, to reduce an operation cost.
Fifth, gas distribution system should be perfectly controlled with feed-forward
control system. This is because gas flow is too late with conventional feedback
systems. His idea is to measure a pressure with a pressure sensor and an
upstream pressure at an orifice, instead of conventional mass-flow controllers.
(111) P-Channel Transistor
Sixth, wafer orientation should be converted to (111) direction plane from
conventional (100) plane. This is because p-channel transistors become faster
with (111) plane, leading to smaller p-channel transistor sizes or higher
integration of a chip.
Seventh, KrF continuous wave (CW) laser should be developed to achieve
narrower beam spectrum, preventing lens deterioration. The emission energy
of 8eV is so strictly controlled that electrodes are kept from damage by F
radicals or ions.
Ohmi stressed the semiconductor industry should design a process equipment
system with academic background. "Academic efforts also contribute to the
semiconductor industry. Industry people should ask the universities to transfer
their R&D research into practical use. We are pleased to show excellent
results for a practical level," he commented with confidence.
(Kenji Tsuda, Tokyo: April 2000 Issue, Nikkei Electronics Asia) |
