Silicon has been the heart of the world's technology boom
for nearly half a century, but microprocessor
manufacturers have all but squeezed the life out of it. The
current technology used to make microprocessors will begin to
reach its limit around 2005. At that time, chipmakers will
have to look to other technologies to cram more transistors
onto silicon to create more powerful chips. Many are already
looking at extreme-ultraviolet lithography (EUVL) as a
way to extend the life of silicon at least until the end of
Photo courtesy Sandia National
Laboratories This wafer was
patterned on a prototype device using
The current process used to pack more and more transistors
onto a chip is called deep-ultraviolet lithography,
which is a photography-like technique that focuses light
through lenses to carve circuit patterns on silicon wafers.
Manufacturers are concerned that this technique might soon be
problematic as the laws of physics intervene.
Using extreme-ultraviolet (EUV) light to carve
transistors in silicon wafers will lead to microprocessors
that are up to 100 times faster than today's most powerful
chips, and to memory chips with similar increases in storage
capacity. In this edition of HowStuffWorks,
you will learn about the current lithography technique used to
make chips, and how EUVL will squeeze even more transistors
onto chips beginning around 2007.
Making Chips Before you learn about how EUV
lithography will revolutionize the manufacturing of microprocessors,
you should first understand a thing or two about current
manufacturing processes. Microprocessors, also called computer
chips, are made using a process called lithography.
Specifically, deep-ultraviolet lithography is used to
make the current breed of microchips and was most likely used
to make the chip that is inside your computer.
Lithography is akin to photography in that it uses light to
transfer images onto a substrate. In the case of a camera, the
substrate is film. Silicon
is the traditional substrate used in chipmaking. To create the
integrated circuit design that's on a microprocessor, light is
directed onto a mask. A mask is like a stencil of the
circuit pattern. The light shines through the mask and then
through a series of optical lenses that shrink the image down.
This small image is then projected onto a silicon, or
The wafer is covered with a light-sensitive, liquid plastic
called photoresist. The mask is placed over the wafer,
and when light shines through the mask and hits the silicon
wafer, it hardens the photoresist that isn't covered by the
mask. The photoresist that is not exposed to light remains
somewhat gooey and is chemically washed away, leaving only the
hardened photoresist and exposed silicon wafer.
The key to creating more powerful microprocessors is the
size of the light's
wavelength. The shorter the wavelength, the more
transistors can be etched onto the silicon wafer. More
transistors equals a more powerful, faster microprocessor.
That's the big reason why an Intel Pentium 4 processor,
which has 42 million transistors, is faster than the
Pentium 3, which has 28 million transistors.
As of 2001, deep-ultraviolet lithography uses a wavelength
of 240 nanometers. A nanometer is one-billionth of a meter. As
chipmakers reduce to 100-nanometer wavelengths, they will need
a new chipmaking technology. The problem posed by using
deep-ultraviolet lithography is that as the light's
wavelengths get smaller, the light gets absorbed by the glass
lenses that are intended to focus it. The result is that the
light doesn't make it to the silicon, so no circuit pattern is
created on the wafer.
This is where EUVL will take over. In EUVL, glass lenses
will be replaced by mirrors to focus light. In the next
section, you will learn just how EUVL will be used to produce
chips that are at least five times more powerful than the most
powerful chips made in 2001.
Moore's Law Each year, manufacturers bring
out the next great computer chip that boosts computing power
and allows our personal
computers to do more than we imagined just a decade ago.
founder Gordon Moore predicted this technology
phenomenon more than 35 years ago, when he said that the
number of transistors on a microprocessor would double every
18 months. This became known as Moore's Law.
Industry experts believe that deep-ultraviolet lithography
will reach its limits around 2004 and 2005, which means that
Moore's law would also come to an end without a new chipmaking
technology. But once deep-ultraviolet hits its ceiling, we
will see chipmakers move to a new lithography process that
will enable them to produce the industry's first 10-gigahertz
(GHz) microprocessor by 2007. By comparison, the fastest Intel
Pentium 4 processor (as of May 2001) is 2.4 GHz. EUVL could
add another 10 years to Moore's Law.
Photo courtesy Sandia National
Laboratories An engineer
inspects a wafer freshly printed from the prototype
"EUV lithography allows us to make chips with feature sizes
that are small enough to support 10 GHz clock speed. It
doesn't necessarily make it happen," Don Sweeney, EUV
Lithography program manager at Lawrence
Livermore National Laboratory (LLNL), said. "The first
thing we need to do is to make integrated circuits down to 30
nanometers, and EUV lithography will clearly do that." By
comparison, the smallest circuit that can be created by
deep-ultraviolet lithography is 100 nanometers.
In April 2001, the EUV Limited Liability Company
(EUV LLC) unveiled the first full-scale prototype EUV
lithography machine. The EUV LLC is a consortium comprised of
some of the world's leading chipmakers and three U.S.
Department of Energy research labs. Members include Intel,
AMD, IBM, Micron, Infeneon and Motorola. These companies are
working with the Virtual National Laboratory, made up
of Sandia National Laboratories, Lawrence Livermore National
Laboratory and Lawrence Berkeley National Laboratory. The
advantage of being a member of this consortium is having first
priority to use this new technology.
Now let's see how EUVL works.
The EUVL Process Here's how EUVL works:
A laser is
directed at a jet of xenon gas. When the laser hits
the xenon gas, it heats the gas up and creates a plasma.
Once the plasma is created, electrons begin to come off
of it and it radiates light at 13 nanometers, which is too
short for the human eye to
The light travels into a condenser, which gathers
in the light so that it is directed onto the mask.
A representation of one level of a computer chip is
patterned onto a mirror by applying an absorber to
some parts of the mirror but not to others. This creates the
The pattern on the mask is reflected onto a series of
four to six curved mirrors, reducing the size of the
image and focusing the image onto the silicon wafer. Each
mirror bends the light slightly to form the image that will
be transferred onto the wafer. This is just like how the
lenses in your camera
bend light to form an image on film.
Image source: Sandia National
According to Sweeney, the entire process relies on
wavelength. If you make the wavelength short, you get a better
image. He says to think in terms of taking a still photo with
"When you take a photograph of something, the quality of
the image depends on a lot of things," he said. "And the first
thing it depends on is the wavelength of the light that you're
using to make the photograph. The shorter the wavelength, the
better the image can be. That's just a law of nature."
As of 2001, microchips being made with deep-ultraviolet
lithography are made with 248-nanometer light. As of May 2001,
some manufacturers are transitioning over to 193-nanometer
light. With EUVL, chips will be made with 13-nanometer light.
Based on the law that smaller wavelengths create a better
image, 13-nanometer light will increase the quality of the
pattern projected onto a silicon wafer, thus improving
This entire process has to take place in a vacuum
because these wavelengths of light are so short that even air
would absorb them. Additionally, EUVL uses concave and convex
mirrors coated with multiple layers of molybdenum and silicon
-- this coating can reflect nearly 70 percent of EUV light at
a wavelength of 13.4 nanometers. The other 30 percent is
absorbed by the mirror. Without the coating, the light would
be almost totally absorbed before reaching the wafer. The
mirror surfaces have to be nearly perfect; even small defects
in coatings can destroy the shape of the optics and distort
the printed circuit pattern, causing problems in chip
For more information on EUVL and related topics, check out
the links on the next page.