Extreme ultra violate lithography

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         Prashant R Jethwa – 08ce038
         V.V.P. Engineering collage.

       The heart of a computer is at the Central Processing Unit, also known as the “CPU”. Over time,
technology has allowed the computer industry to make the size of the CPU smaller than ever imagined. The
technology used to create these processor chips is called Lithography. Unfortunately this technology can only
go so far. What happens when its capabilities are exhausted and it can no longer improve the size and amount
of information held on the CPU? The proposed solution to this problem is known as EUVL, Extreme
Ultraviolet Lithography. In this paper I will discuss who is involved in the EUVL project, what it promises
for the computer industry, what EUV technology is, and how it works.

Who is Involved in EUVL?

        The EUVL project resulted from the first U.S. computer-chip maker consortium known as Sematech.
The consortium consisted of both government and private funding to improve U.S. chip-making systems. It
was developed by the democrats, but also partly stemmed from the end of the Ronald Reagan administration
and his Strategic Defense Initiative. The EUVL project is the successor of Sematech and was launched in
1997 as a way for the U.S. to revive and improve its stepper industry next to the Japanese.

       The project consists of three national labs: Sandia, Lawrence Livermore, and Lawrence Berkeley.
Together these three laboratories have been working together in a “virtual national lab.” Each of the three
labs provides a fundamental necessity for the EUV project. Livermore focuses on high-end optics, precision
engineering, and multilayer coatings. Sandia brings in systems engineering, resists, and a light source.
Berkeley, like Sandia, provides a light source, but one that’s more advanced to work with the optics and
resists in the EUV light range. Funding for the EUV project came from companies such as Intel and AMD
(Advanced Micro Devices), Motorola, and IBM. The total amount of funding came to about $250 million.
What EUVL Promises?

        EUVL is the technology that will keep “Moore’s Law” alive for about ten more years. “Moore’s Law”
states that the numbers of transistors on a microprocessor chip will double every 18 months. Without the
EUVL project, “Moore’s Law” would become obsolete by 2004 or 2005 along with DUV (Deep-Ultraviolet)
light reaching its maximum limit of use. Currently, the fastest working microprocessor is the Pentium 4,
which is 2.4-gigahertz (GHz). The implementation of EUVL could produce a 10GHz microprocessor by

        Currently the UV light functions at a wavelength of 0.248 micrometers. Using UV light allows the
ability to create features on a chip as small as 0.25 micrometers. It’s predicted that in under 10years the size
of the chip features will be as small as 0.13 micrometers by using wavelengths of 0.193 micrometers. In order
to create smaller features, a new light source is needed. This is where the EUVL project comes into play.
EUVL in simplicity uses EUV light and mirrors to reflect the light instead of lenses. If lenses were used, too
much light would be absorbed and it would be impossible to etch the patterns on the silicon wafer.

        According to Don Sweeney, EUVL program manager at Lawrence Livermore National Laboratory
(LLNL), “EUV lithography allows us to make chips with feature sizes that are small enough to support a
10GHz clock speed. It doesn’t necessarily make it happen.” Sweeney also states that in order to create these
chips, “The first thing we need to do is to make integrated circuits down to 30 nanometers, and EUV
lithography will clearly do that.”

What is lithography?

        Lithography originally used an image drawn in wax, or other oily substance applied to a lithographic
stone as the medium to transfer ink to the printed sheet. In modern times, the image is often made of polymer
applied to a flexible aluminum plate. The flat surface of the plate or stone is slightly roughened or etched, and
divided into hydrophilic regions that accept a film of water and while wet repel greasy ink, and hydrophobic
regions which repel water and accept ink because the surface tension is higher on the greasier image area
which remains dry. The image may be printed directly from the stone or plate (in which case it is reversed
from the original image) or may be offset by transfer to a flexible sheet, usually rubber, for transfer to the
printed article.
       This process is different from gravure or intaglio printing where a plate is engraved, etched or stippled
to make cavities to contain the printing ink, and in woodblock printing and letterpress where ink is applied to
the raised surfaces of letters or images.

What is EUVL Technology?

       EUVL (Extreme Ultraviolet Lithography) is the replacement to DUVL (Deep Ultraviolet Lithography)
in the microprocessor industry. Lithography is similar to photography in the sense that they both create a print
on a chosen medium. In simplicity, photography creates pictures on paper while lithography creates imprints
on silicon wafers. How this is done will be explained in the next section.

How EUV Lithography Works?

   1. 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.
   2. 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 see.
   3. The light travels into a condenser, which gathers in the light so that it is directed onto the mask. The
       mask is what contains the design of the computer chip being made.
   4. 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 mask.
   5. 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. .
6. The wafer that the image is projected on is coated with a light-sensitive gel called photoresist. The
   light that is allowed through the mask hardens the photoresist when it hits it. Whatever is left of the
   gel on the wafer is then chemically washed away. The result is a silicon wafer that is ready to be used
   in a computer.

   In lithography, the type of light and its wavelength have a direct effect on the power of the computer
chip being made. A shorter wavelength equals more transistors which equals a more powerful chip. To
get an idea of how this is seen in the computer world, a Pentium 3 microprocessor has 28 million
transistors, while a Pentium 4 has 42 million transistors.
         One of the most crucial factors for EUVL being successful is the environment it is done in. Because
EUV light has such a short wavelength, it can be absorbed by air. To avoid this problem in the EUVL
process, the machine creating the microprocessor must function as a vacuum. By functioning as a vacuum,
the machine doesn’t allow air to enter and absorb the EUV light. One other alternative that was considered
along with EUV was X-rays. Unfortunately x-rays were too destructive and couldn’t be used as a light
source. The EUV light is at a wavelength that exists between DUV and x-rays. This wavelength allows for
creating smaller and more transistors on a chip while at the same time, not destroying the chip like x-rays

Image formation mechanism

Top: EUV multilayer and absorber (purple) constituting mask pattern for imaging a line.

Bottom: EUV radiation (red) reflected from the mask pattern is absorbed in the resist (amber) and substrate
(brown), producing photoelectrons and secondary electrons (blue). These electrons increase the extent of
chemical reactions in the resist. A secondary electron pattern that is random in nature is superimposed on the
optical image. The unwanted secondary electron exposure results in loss of resolution, observable line edge
roughness and line width variation.
       Lithography is akin to photography in that it uses light to transfer images onto a substrate. Silicon is
the traditional substrate used in chip making. 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 semiconductor, wafer.


       The computer industry is constantly growing and at a very fast pace. In order to keep up with this fast
pace, technology must progress at an equal if not faster pace. The current result of technology advancing is
the EUVL project. With any luck, EUVL will improve the chip making industry and stay at the same pace.
As for when EUVL will become obsolete; the industry can only guess on that, but hopefully improvements to
EUVL won’t be necessary for quite a few years.

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