San
Jose, Calif. (February 20, 2006) IBM
researchers today announced they have found a way
to extend a key chip-manufacturing process to generate
smaller chip circuits, potentially postponing the
semiconductor industry's high-risk conversion to
an extremely expensive alternative.
IBM scientists have created the smallest, high-quality
line patterns ever made using deep-ultraviolet
(DUV, 193-nanometer) optical lithography a technology
currently used to essentially print circuits on chips. The distinct and uniformly
spaced ridges are only 29.9 nanometers wide (a nanometer is a billionth of a
meter). This is less than one-third the size of the 90-nanometer features now
in mass production and below the 32 nanometers that industry consensus held as
the limit for optical lithography techniques.
For decades, the semiconductor industry has relied on continually shrinking
circuits to drive increases in the performance and function of chips and the
products that use them. But as chip features now approach the fundamental scale
limits of individual atoms and molecules, the future of this trend of relentless
improvement, known as Moore's Law, is being threatened. IBM's new result indicates
that a "high-index
immersion" variant of DUV lithography may provide a path for extending Moore's
Law further, thus buying the industry time.
Our goal is to push optical lithography as far as we can so the industry does
not have to move to any expensive alternatives until absolutely necessary," said
Dr. Robert D. Allen, manager of lithography materials at IBM's Almaden Research
Center. "This result is the strongest evidence to date that the industry may
have at least seven years of breathing room before any radical changes in chip-making
techniques would be needed."
The record-small pattern of well-defined and equally spaced 29.9-nanometer lines
and spaces was created on a lithography test apparatus designed and built at
IBM Almaden, using new materials developed by its collaborator, JSR Micro (Sunnyvale,
California). The first technical details will be presented this week (Monday,
Feb 20, 2006) at the SPIE Microlithography 2006 conference being held in San
Jose, California.
We believe that high-index liquid imaging will enable the extension of today's
optical lithography through the 45- and 32-nanometer technology nodes, said
Mark Slezak, technical manager of JSR Micro, Inc. Our industry faces tough questions
about which lithography technology will allow us to be successful below 32 nanometers.
This new result gives us another data point favoring the continuation of optical
immersion lithography.
Technical details
Microelectronic chips are made by a process called photolithography, which
is similar in concept to silk-screening except it uses light instead of paint
or ink. Photolithography transfers the various circuit design patterns onto a
silicon wafer by projecting a uniform beam of laser light through a shadow mask
and then focusing it onto a photosensitive "photoresist" material that coats
the silicon wafer. Subsequent development, etching, and materials deposition
steps form the circuit features. Making a typical computer processor or memory
chip may require dozens of photolithography cycles.
Over the years, the industry has created smaller circuit features which typically
lead to smaller, faster and cheaper electronics -- by using ever-shorter wavelengths
of light, stronger lenses and most recently inserting between the final lens
and the silicon wafer a liquid, currently water, that enables even finer resolution.
Until now, it was not known if the industry could continue to adapt this optical
immersion technique to produce sharp features smaller than 32 nanometers. New
materials required to make such small features were thought to be incompatible
with each other or capable of yielding only indistinct, blurred patterns. As
a result, in recent years contingency plans are being explored for switching
sometime in the future to a radically different but much more expensive and
still unproven -- manufacturing method that uses soft-x-rays (also known as EUV,
for extreme ultraviolet light) and exotic mirrors rather than laser light and
lenses.
As part of its efforts to extend current optical lithography techniques, IBM
developed an industry-leading interference immersion lithography test apparatus,
called NEMO. IBM's NEMO tool uses two intersecting laser beams to create light-and-dark
interference patterns with spacings closer than can be made with current chip-making
apparatus. As a result, NEMO is ideal for researching, testing and optimizing
the various high-index fluids and photoresists being considered for use in those
future DUV systems that would create such fine features. Now that IBM's new result
shows a path for extending optical lithography, high-index lens materials must
be developed to enable its commercial viability.
When light passes through a transparent material, it slows down in proportion
to the material's "refractive index." Light passing through a higher-index material
has a shorter wavelength and can thus be focused more tightly. Resolution in
immersion lithography is limited by the lowest refractive index of the final
lens, fluid and photoresist materials. In IBM's NEMO experiments, the lens and
fluid had indices of about 1.6, and the photoresist's index of refraction was
1.7. Future research is aimed at developing lens, fluid and photoresist materials
with indices of refraction of 1.9, which would enable even smaller features to
be imaged.
Related links:
Additional info:
On Monday (Feb 13) at the White House, IBM
received a National Medal of Technology for our many innovations to the
semiconductor industry, which include many from Almaden, such as:
- Chemically amplified photoresists: A mixture of cleverly designed light-sensitive
materials enables ever-smaller circuit features to be transferred to silicon
and manufactured. This seminal development has enabled the industry to improve
computer circuits and memories at its famously torrid Moore's Law pace for
the past 15 years and on into the future. (First research results: 1982;
industry impact: 1990 to present.)
- Using excimer lasers to make chips: When first developed, excimer lasers
were noted for their power and efficiency at desireably short wavelengths.
But many scientists believed that laser light was not suitable for chip making.
IBM San Jose researchers figured out how to tune and control the output of
excimer lasers to create the required optical quality. (Research result:
1977; industry impact: mid 1980s to present)
- Phase-shifting masks: To make chip features as small as are needed today,
a simple shadow mask no longer works. By playing tricks with the wave nature
of light -- phase shifting -- the light can produce smaller and sharper features
than had been possible before. (Research result: 1982; industry impact 2000
to present.)
- First demonstration of the chip-making potential of immersion lithography:
Placing a high-index liquid between the final lens and the silicon wafer
can enable a light source to produce smaller features. This chip industry
has recently adopted immersion lithography to make next-generation (65nm)
features. (Research result: 1999; industry impact: 2003 to present)
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