49 Extreme Ultraviolet Lithography

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Extreme Ultraviolet Lithography Seminar Report 2010

1. INTRODUCTION

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 2 !. "t that time,

chipmakers will have to look to other technologies to cram more transistors

onto silicon to create more powerful chips. #any are already looking at

extreme-ultraviolet lithography $%& () as a way to e*tend the life of

silicon at least until the end of the decade.

+otential successors to optical pro ection lithography are being

aggressively developed. These are known as - e*t/0eneration (ithographies-

$ 0('s). %& lithography $%& () is one of the leading 0( technologies1

others include */ray lithography, ion/beam pro ection lithography, and

electron/beam pro ection lithography. &sing extreme-ultraviolet $%& ) light

to carve transistors in silicon wafers will lead to microprocessors that are up to

times faster than today's most powerful chips, and to memory chips with

similar increases in storage capacity.

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2. EUVL DE!INITION

%*treme ultraviolet lithography $%& () is an advanced

technology for making microprocessors a hundred times more powerful than

those made today.

%& ( is one technology vying to replace the optical lithography

used to make today's microcircuits. 3t works by burning intense beams of

ultraviolet light that are reflected from a circuit design pattern into a silicon

wafer. %& ( is similar to optical lithography in which light is refracted

through camera lenses onto the wafer. 4owever, e*treme ultraviolet light,

operating at a different wavelength , has different properties and must be

reflected from mirrors rather than refracted through lenses. The challenge is to

build mirrors perfect enough to reflect the light with sufficient precision

2.1 EUV R"DI"TION

5e know that &ltraviolet radiations are very shortwave

$very low wavelength) with high energy. 3f we further reduce the wavelength

it becomes %*treme &ltraviolet radiation. 6urrent lithography techniques have

been pushed ust about as far as they can go. They use light in the deep

ultraviolet range/ at about 278/nanometer wavelengths/to print ! / to 2 /nanometer/size features on a chip. $" nanometer is a billionth of a meter.) 3n

the ne*t half dozen years, manufacturers plan to make chips with features

measuring from to 9 nanometers, using deep ultraviolet light of :;/ and

!9/nanometer wavelengths.


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2.2 LIT#O$R"%#&

6omputers have become much more compact and

increasingly powerful largely because of lithography, a basically photographic

process that allows more and more features to be crammed onto a computer

chip.

(ithography is akin to photography in that it uses

light to transfer images onto a substrate. (ight is directed onto a mask/a sort

of stencil of an integrated circuit pattern/and the image of that pattern is then pro ected onto a semiconductor wafer covered with light/sensitive photoresist.

6reating circuits with smaller and smaller features has required using shorter

and shorter wavelengths of light.

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'. (#& EUVL)

The current process used to pack more and more

transistors onto a chip is called *eep-ultraviolet lithography , which is a

photography/like technique that focuses light through lenses to carve circuit

patterns on silicon wafers. #anufacturers are concerned that this technique

might soon be problematic as the laws of physics intervene.

3ntel, "#= , and #otorola have oined with the &.S.

=epartment of %nergy in a three/year venture to develop a microchip with

etched circuit lines smaller than . micron in width. $Today's circuits are

generally . 8 micron or greater.) " microprocessor made with the %& (

technology would be a hundred times more powerful than today's. #emory

chips would be able to store , times more information than they can

today. The aim is to have a commercial manufacturing process ready before

2 !.

+rocessors built using %& technology are e*pected to

reach speeds of up to 04z in 2 !/2 >.


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ago, when he said that the number of transistors on a microprocessor would

double every 8 months. This became known as +oore/0 La .

3ndustry e*perts believe that deep/ultraviolet lithography

will reach its limits around 2 7 and 2 !, which means that #oore's law

would also come to an end without a new chipmaking technology.


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than across town@ the electronic signals zipping around the circuitry to solve

computing problems have less distance to travel. Today's chip contains about

;,2> times more transistors than the chip of :9 .

" microprocessor // also known as a C%U or central

processing unit // is a complete computation engine that is fabricated on a

single chip. The first microprocessor was the 3ntel 7 7, introduced in :9 .

The 7 7 was not very powerful // all it could do was add and subtract, and it

could only do that 7 bits at a time. to the 8 ;8> to the

8 78> to the +entium to the +entium 33 to the +entium 333 to the +entium 7. "ll

of these microprocessors are made by 3ntel and all of them are improvements

on the basic design of the 8 88. The +entium 7 can e*ecute any piece of code

that ran on the original 8 88, but it does it about !, times fasterA

" microprocessor sometimes called a logic chip . 3t is

the -engine- that goes into motion when you turn your computer on. "

microprocessor is designed to perform arithmetic and logic operations that

make use of small number/holding areas called registers . Typical

microprocessor operations include adding, subtracting, comparing two

numbers, and fetching numbers from one area to another. These operations are

the result of a set of instruction s that are part of the microprocessor design.

5hen the computer is turned on, the microprocessor is designed to get the

first instruction from the basic inputBoutput system $


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program is -driving- the microprocessor, giving it instructions to perform. The

following table helps you to understand the differences between the different

processors that 3ntel has introduced over the years.

Name Date Transistors Microns ClockspeedDatawidth MIPS

8080 1974 6,000 6 2 MHz 8 bits 0.64

8088 1979 29,000 3 5 MHz

16bits8-bitbus

0.33

80286 1982 134,000 1.5 6 MHz 16bits 1

80386 1985 275,000 1.516

MHz32

bits5

80486 1989 1,200,000 125

MHz32

bits20

Pentium 1993 3,100,000 0.860

MHz

32bits

64-bitbus

100

Pentium II 1997 7,500,000 0.35233MHz

32bits

64-bitbus

~300

Pentium III 1999 9,500,000 0.25450MHz

32bits

64-bitbus

~510

Pentium 4 2000 42,000,000 0.181.5

GHz

32bits

64-bitbus

~1,700

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4. EUVL TEC#NOLO$&

3n many respects, %& ( retains the look and feel of

optical lithography as practiced today. Dor e*ample, the basic optical design

tools that are used for %& imaging system design and for %& image

simulations are also used today for optical pro ection lithography.

onetheless, in other respects %& ( technology is very different from what

the industry is familiar with. #ost of these differences arise because the

properties of materials in the %& are very different from their properties in

the visible and & ranges.

Doremost among those differences is the fact that %&

radiation is strongly absorbed in virtually all materials, even gases. %&

imaging must be carried out in a near vacuum. "bsorption also rules out the

use of refractive optical elements, such as lenses and transmission masks.

Thus %& ( imaging systems are entirely reflective. 3ronically, the %&

reflectivity of individual materials at near/normal incidence is very low. 3n

order to achieve reasonable reflectivityEs near normal incidence, surfaces must

be coated with multilayer, thin/film coatings known as distributed


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trend with strong investments in %*treme &ltraviolet $%& ) research at our

4illsboro, Cregon, and Santa 6lara, 6alifornia, sites.

The completion of the prototype machine $%ngineering

Test Stand) marks a ma or milestone for the program, since we have proven

that %& lithography works,- said 6huck 0wyn, program manager of the

%& (imited (iability 6ompany. -Cur ne*t step is to transfer the technology

to lithography equipment manufacturers to develop beta and production

tools.-

+rocessors built using %& technology are e*pected to reach speeds of up to 04z in 2 !/2 >.


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5. #O( EUV C#I%+"3IN$ (OR3

Dor describing the %& chipmaking process we should

have a clear idea of chipmaking process.


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5.1 C#I%+"3IN$

(ithography is akin to photography in that it uses light to

transfer images onto a substrate. 3n 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 ma06 . "

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 pro ected onto a silicon, or semiconductor, wafer.

The wafer is covered with a light/sensitive, liquid plastic

called photore0i0t . 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 e*posed to light remains

somewhat gooey and is chemically washed away, leaving only the hardened

photoresist and e*posed 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. #ore transistors equals a more powerful,

faster microprocessor. That's the big reason why an 3ntel %e tium 4 processor,

which has 72 million transistors, is faster than the %e tium ' , which has 28million transistors.

"s of 2 , deep/ultraviolet lithography uses a wavelength of

27 nanometers. " nanometer is one/billionth of a meter. "s chipmakers

reduce to /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

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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 %& ( will take over. 3n %& (, glass lenses

will be replaced by mirror0 to focus light. 3n the ne*t section, you will learn

ust how %& ( will be used to produce chips that are at least five times more

powerful than the most powerful chips made in 2 .

The components on a microchip are made by carving patterns

into layers of doped and undoped silicon. 3n the standard technique, light isshone through a stencil onto a silicon wafer that is coated with a light/

sensitive polymer known as a resist. 6hemical etching then removes the

regions of silicon coated with either the une*posed or the e*posed polymer,

until the desired structure is achieved. Dinally, the remaining polymer is

washed off.


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5.2 T#E EUVL %ROCE

4ere's how %& ( works@

. " laser is directed at a et of xe o ga0 . 5hen the laser hits the *enon

gas, it heats the gas up and creates plasma.

This source of e*treme ultraviolet light is based on a

plasma created when a laser is focused on a beam of *enon gas clusters

e*panding at supersonic speeds. $


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E gi eeri g Te0t ta *

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;. The light travels into a 7o *e 0er , which gathers in the light so that it is

directed onto the ma06 .

7. " representation of one level of a computer chip is patterned onto a

mirror by applying an a80or8er to some parts of the mirror but not to

others. This creates the mask.

!. The pattern on the mask is reflected onto a series of four to si* 7urve*

mirror0 , reducing the size of the image and focusing the image onto

the silicon wafer. %ach mirror bends the light slightly to form the image

that will be transferred onto the wafer. This is ust like how the lenses

in your camera bend light to form an image on film .

The %TS $%ngineering Test Stand, also called prototype

machine) includes a condenser optics bo* and a pro ection optics bo*.


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The main role of the condenser optics bo* is to bring light

to the reflective pattern on the mask. -5e want to bring as much light to the

mask and, ultimately, the wafer, as possible,- e*plains Sweeney. -The more

light we deliver, the shorter the e*posure time. 3t's like taking a picture with a

camera. " picture taken in bright noonday sun requires a shorter e*posure

time than does a picture of the same scene taken at twilight.-

Dor the semiconductor industry, brighter %& images

mean shorter e*posure times, which translate to manufacturing more chips at

a faster rate. The optics design team from (awrence (ivermore and Sandia

designed a condenser optics system that collects and transports a significant

fraction of the %& light from the source to the reflective mask.

Cnce the image is reflected from the mask, it travels through the pro ection

optics system. "ccording to Sweeney, the pro ection optics bo* is the optical

heart of the lithographic e*posure system. -3t is to the system what an engine

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is to a car,- he e*plains. The four mirrors of the %TS pro ection optics system

reduce the image and form it onto the wafer. -"gain, imagine using a pocket

camera. The camera lens transmits an image to the film, which/like the wafer/

has a light/sensitive surface,- says Sweeney.

The optics teams are now working on advanced designs for

the pro ection optics. They have a si*/mirror design that promises to e*tend

%& ( systems so that they can print features as small as ; nanometers/ a

significant ump from the 9 /nanometer limit of the %TS. "ccording to

Sweeney, e*tendability to smaller features is an important requirement for whatever lithographic technology the semiconductor industry finally decides

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This wafer was patterned on a prototype device using e*treme/

ultraviolet lithography $%& ().

This wafer was patterned on an integrated laboratory

research system capable of printing proof/of/principle, functioning

microelectronic devices using e*treme ultraviolet lithography $%& (). The

%& lithography research tool was assembled at Sandia ational (aboratories

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in (ivermore, 6alif., which has oined with two other =epartment of %nergy

laboratories / (awrence (ivermore ational (aboratory and (awrence


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percent is absorbed by the mirror. 5ithout the coating, the light would be

almost totally absorbed before reaching the wafer. The mirror surfaces have to

be nearly perfect1 even small defects in coatings can destroy the shape of the

optics and distort the printed circuit pattern, causing problems in chip

function. 4ence


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9. CONCLU ION

%*treme &ltraviolet (ithography $%& () will open a new

chapter in semiconductor technology. 3n the race to provide the

e*t 0eneration (ithography $ 0() for faster, more efficient computer

chips, %& (ithography is the clear frontrunner. "t %& Technology,

Successful implementation of %& ( would enable

pro ection photolithography to remain the semiconductor industry's patterning

technology of choice for years to come. 4owever, much work remains to be

done in order to determine whether or not %& ( will ever be ready for the

production line. Durthermore, the time scale during which %& (, and in fact

any 0( technology, has to prove itself is somewhat uncertain.

Several years ago, it was assumed that an 0( would beneeded by around 2 ! in order to implement the . um generation of chips.

6urrently, industry consensus is that :;nm lithography will have to do the

ob, even though it will be difficult to do so. There has recently emerged talk

of using light at !9 nm to push the current optical technology even further,

which would further postpone the entry point for an 0( technology. 3t thus

becomes crucial for any potential 0( to be able to address the printing of

feature sizes of ! nm and smallerA %& ( does have that capability.

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:. RE!ERENCE

www.intel.com

www.howstuffworks.com

www.sandia.com

www.whatis.com

www.euvl.com www.llnl.com

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"C3NO(LED$E+ENT

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" TR"CT

Silicon has been the heart of the world's technology boom

for nearly half a century. %ach year, manufacturers bring out the ne*t great

computer chip that boosts computing power and allows our +ersonal

6omputers to do more than we imagined ust a decade ago. The current

technology used to make microprocessors, deep ultraviolet lithography will

begin to reach its limit around 2 !. "t that time, chipmakers will have to

look to other technologies to cram more transistors onto silicon to create

powerful chips. #any are already looking at e*treme/ultraviolet lithography

$%& () as a way to e*tend the life of silicon at least until the end of the

decade.

"kin to photography, lithography is used to print circuits

onto microchips %*treme &ltraviolet (ithography $%& () will open a new

chapter in semiconductor technology. 3n the race to provide the e*t

0eneration (ithography $ 0() for faster, more efficient computer chips,

%& (ithography is the clear frontrunner. 4ere we discusses the basic

concepts and current state of development of %& lithography $%& (), a

relatively new form of lithography that uses e*treme ultraviolet $%& )

radiation with a wavelength in the range of to 7 nanometers $nm) to carry

out pro ection imaging. %& ( is one technology vying to become thesuccessor to optical lithography.

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CONTENT

1. INTRODUCTION

2. EUVL DE!INITION

2.1 EUV R"DI"TION

2.2 LIT#O$R"%#&

'. (#& EUVL)

'.1 +OORE, L"(

'.2 INCREDI LE #RIN3IN$ C#I%

4. EUVL TEC#NOLO$&

5. #O( EUV C#I%+"3IN$ (OR3

5.1 +"3IN$ C#I%

5.2 T#E EUVL %ROCE

9. CONCLU ION

:. RE!ERENCE

Dept. of /2!/

49 Extreme Ultraviolet Lithography

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