CEA - Microelectronics · From the electron to chip manufacturing 8w Microelectronics 4 w A...

> INTRODUCTION

De l’électron à la fabrication des puces 8 > La microélectroniqueDe l’électron à la fabrication des puces 8 > La microélectronique

FROM RESEARCH

TO INDUSTRY

w From the electron to chip manufacturing

1 w The atom2 w Radioactivity3 w Radiation and man4 w Energy5 w Nuclear energy: fusion and fission6 w How a nuclear reactor works7 w The nuclear fuel cycle8 w Microelectronics9 w The laser: a concentrate of light10 w Medical imaging11 w Nuclear astrophysics12 w Hydrogen13 w The Sun14 w Radioactive waste15 w The climate16 w Numerical simulation17 w Earthquakes18 w The nanoworld

8 wMicroelectronicsMicroelectronics

© French Alternative Energies and Atomic Energy Commission, 2010Communication DivisionHead Office91191 Gif-sur-Yvette – www.cea.fr

ISSN 1637-5408.

THE COLLECTION

1 w The atom2 w Radioactivity3 w Radiation and man4 w Energy5 w Nuclear energy: fusion and fission6 w How a nuclear reactor works7 w The nuclear fuel cycle8 w Microelectronics9 w The laser: a concentrate of light10 w Medical imaging11 w Nuclear astrophysics12 w Hydrogen13 w The Sun14 w Radioactive waste15 w The climate16 w Numerical simulation17 w Earthquakes18 w The nanoworld

FROM RESEARCH

TO INDUSTRY

A TECHNOLOGICAL REVOLUTIONA BRIEF HISTORYHOW ARE INTEGRATED CIRCUITS MADE?NANOELECTRONICS

> INTRODUCTION

From the electron to chip manufacturing 8w Microelectronics

> CONTENTS 32

introductionCell phones, digital cameras, MP3 players, PCs,

games consoles, bank cards, cars: in just afew decades, integrated circuits or "chips" havetaken over most of the things we use everyday. This takeover is unprecedented in the history oftechnology. It reflects the accelerated pace ofinnovation in the microelectronics industry,which has gone on producing ever smaller tran-sistors, resulting in turn in more powerful andefficient integrated circuits. In 1971, the Intel 4004 processor containedapproximately 2,300 transistors. In 2006, theprospect emerged of chips with a billion tran-sistors. This amazing yet compact intelligenceis becoming cheaper and cheaper: in 1973, itcost the price of an apartment to manufacturea million transistors; today it costs the price ofa post-it.

“Can electronic chips, which are constantlybecoming more powerful and cheaper, goon being miniaturized?”

Yet the outlook for the microelectronics industryis far from clear. Transistors will soon becomeso small that they will be extremely difficultto manufacture and operate. For example, thethickness of some (oxide) insulators may beno greater than 1 nm, that is, 3 or 4 oxideatomic layers!Industry, research laboratories and institutesare setting in place research programs backedby heavy investment. This is especially the casein the Grenoble region, a world-class centerfor microelectronics. It is home to the CEA’sLETI (Laboratory of Electronics and Informa-tion Technology) and ST Microelectronics manu-facturing in Crolles site combine forces. Finally,4,000 people have been working in Grenoblesince 1976 at Minatec, the leading Europeaninnovation cluster for micro and nanotechno-logies.

A TECHNOLOGICAL REVOLUTION 4Making microelectronicsmore widely accessible 5More complex calculations 6Innovative productsand services 7

A BRIEF HISTORY... 8The diode, the key electronic device 9From transistor to integratedcircuit 10Modern integrated circuits 11

HOW ARE INTEGRATED CIRCUITS MADE? 13Increasingly expensive plants 14The clean room, an ultra pure environment 15Mass production 16Basic operations 17

NANOELECTRONICS 18Top down and bottom up 19The way forward for nano-technologies 19

w INTRODUCTION 3

Microelectronics

Observation of a silicon wafer using an optical microscope.


Conception et réalisation: – www.specifique.fr – Caption of cover: Substrate on support © P.Stroppa/CEA – Cover: © CEA – P.Stroppa/CEA – Illustrations: Yuvanoé -Printed by: Imprimerie Sénécaut – Summer 2010

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Microelectronicsenables newapplications onaccount of itsminiaturization andhigh performance.For example inmedicine with thisDNA-chip(on the right)


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In order to maintain this pace of development,we must constantly call into question: the mate-rials used for circuits, electrical connectionsand insulators; circuit architectures, whichrepresent a decisive factor in the final perfor-mance; production equipment, some of it costing several million euros; the size of thesilicon wafers on which circuits are produced(200 mm and 300 mm), along with all themethods used in their manufacture.To attain this level of performance, the mostsignificant factor is how thin the etchings are.Initially this was expressed inmicrons (millionths of a meter):0.25 micron, then 0.18 micron,

“On a 45 nm printed circuit the etchingsare a thousand times thinner than ahair.”

40 YEARS OF CONTINUOUS PROGRESS ANDNEW PRODUCTS AND SERVICES LIE BEHINDTHE AGE OF MINIATURIZATION.

MAKING MICROELECTRONICSMORE WIDELY ACCESSIBLEMicroelectronics is not an established and stabilized business. The number of transistorsper unit area quadruples every three years andthe cost of the circuits halves every 18 months,particularly through mass production of hun-dreds of chips on each silicon wafer. This growth curve in performance was described in 1965 by Gordon Moore, cofounderof Intel Corporation. It has proven so accuratethat it is now known as "Moore's law" by all themanufacturers in the sector, who rely upon itto plan their investments and research programsyears in advance.


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A technologicalA technologicalrevolutionrevolution

MOORE LAW

This technic definethe width of thepatterns molded on the silicon.

chip

performance reaches the teraflop.Advances in integrated cir-cuits are the cause of thisgiant leap, which has opened new possibilities:- The design of complex systems or products.This can be done entirely on computer. Depen-ding on the expected conditions of use, the com-puter calculates the behavior of the materials,the dimensions of the components, and theirspatial layout, and then draws the plans.- Phenomenological modeling. The behavior ofan airliner in turbulence or five-day changes inthe weather depend on a whole host of para-meters. They can be modeled, that is repre-sented by a series of complex operations whoseresult is very close to the actual phenomenon.- Computer simulation. This time the processinvolves "manipulating" the models. For example,by providing the weight of the aircraft and itsspeed, plus the strength and direction of theturbulence, the computer can then predict its

and then 0.13 micron. Since the turn of thecentury, the most commonly used unit is nowthe nanometer (a billionth of a meter). A pro-duction facility like Crolles produces 45 nm cir-cuits or etchings a thousand times finer thanthe thickness of a hair.These technological achievements have led toa fall in costs, an increased level of performanceand more widespread use of microelectronics,with two consequences: constantly increasingcomputer power and new products and servicesfor the general public.

MORE COMPLEX COMPUTATIONFOR DESIGN, SIMULATION ANDMODELING...Post-war scientists carried out their calcula-tions on computers that occupied entire rooms,and whose performance was no greater thanthat of a modern calculator. Early twenty-firstcentury scientists have supercomputers whose

From the electron to chip manufacturing 8w MicroelectronicsFrom the electron to chip manufacturing 8w Microelectronics

w A TECHNOLOGICAL REVOLUTION 76 w A TECHNOLOGICAL REVOLUTION

in-flight behavior. In design terms, computersimulation allows an engine to be tested, forexample, before producing a prototype, to seehow it will be affected by heating, road vibra-tions or shocks.

INNOVATIVE PRODUCTS AND SERVICESThe computing power of integrated circuits canoffer the general public high-performance,user-friendly equipment, with a whole rangeof features: cell phones, DVD players, digitaltelevisions, MP3 players, digital cameras, bankcards, and so on. The chips power both thecomputing functions and the interfaces (suchas the keyboard, display, and USB) that makethem intuitive and easy to use. Moreover, the size and price of the productsare steadily decreasing. The consumer is thewinner on all fronts. The cell phone providesa perfect illustration of this phenomenon. Thefirst devices, which were very bulky, could “only”©

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“The power of current supercomputers can reach1,000 billion operations per second... thanks toadvances in microelectronics.”

ENIAC, the first computer. Tera, the new supercomputer.

1,000 billion operations persecond.

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INTERNAL DESIGN OF AN MP3 PLAYER

be used to make telephone calls. The latestmodels are ultra-lightweight and feature games,HD cameras, and Internet connection for thesame price or less. Finally, it should be borne in mind that mostsuch equipment includes not one but severalintegrated circuits (microprocessors andmemory) that have been carefully designed towork together and enhance the overall perfor-mance of the device.

“The most successfulconsumer products have more features, are more compact,and cheaper.”

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Microprocessor Controls the operating system and software

Flash memory A way of storing musicwithout using power

USB flash drive Controls and encodes theconnection with the computer Computer

Manages the coding and decodingof sound using psychoacoustic

algorithms

Keyboard and display Display and data retrieval,

user interface

Analog-digitalconverter

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THE DIODE, THE KEY ELECTRONICDEVICEThe history of electronics began in 1904 withthe invention of the diode, used in radio sets.A diode is a vacuum device comprising a fila-ment that emits electrons and a plate that collects electrons when it is positively charged(electrons have a negative charge). The posi-tive or negative voltage of the plate is changedin order to make or break the flow of current.In 1907 the triode appeared, in which a gridis added between the filament and the plate.This grid acts as a modulator of the electrons:depending on its polarization, it either blocksthem or makes them flow faster (current ampli-fication). During the 1940s, triodes and other types ofvalves were used in the first electronic compu-ters capable of performing calculations fasterthan a human being. The numbers and taskswere coded in binary, using 0 or 1. For instance,1 corresponds to the flow of electrical current,0 to it being stopped. However, to carry out

complex calculations such as those required byphysicists, the number of vacuum tubes needsto be multiplied, and they are bulky, producelots of heat and “fail” easily. This lack of relia-bility held back the development of computing.

IN A CENTURY, MINIATURIZATION HAS ENABLEDTHE TRANSITION FROM THE VACUUM TUBE TOTHE ONE-MICROMETER-SQUARE TRANSISTOR.

Vacuum diodes and transistors from 1965 (above).

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1904John Alexander Fleming, anEnglish engineer, invents thediode. This was the first electronicdevice and was used in radioreceivers. In 1907, Lee de Forest,an American researcher, developsthe principle further by inventingthe triode.

1954Texas Instruments manufacture thefirst silicon transistor. They werethe size of dice, but within adecade would be as small as agrain of salt. However, the vastnumber of connecting threadsholds back the development ofcomplex circuits.

a few key dates in the history of microelectronics a few key

WHERE DOES THE WORD “BUG” COME FROM?

The English word bug usually denotes an insect or"creepy crawly". So then how is this connected with thebugs in software? It is quite simple. With ENIAC, theworld’s first computer, developed at the University ofPennsylvania in 1946, a major cause of failure wassmall butterflies landing on electrical connections.

These were all the more numerous because ENIACwas a 30-ton monster, occupying 72 square m andusing more than 17,000 vacuum tubes.

This was how bugs came to be part of the world ofcomputing…

1948John Bardeen, Walter Brattain andWilliam Shockley, three physicistsat the Bell Laboratories (USA),produce the first transistor.Reliability, smaller size, reducedpower consumption: the route tominiaturization opens up. Thismajor discovery would win themthe Nobel Prize for Physics in1956.A brief history...A brief history...

w A BRIEF HISTORY...


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Within a few years, they went from being thesize of dice to the size of a grain of salt! The transistor was used in new radio sets - towhich it gave its name - and in computers.Yet another obstacle quickly became apparent:the more transistors there were, the more weldedcopper threads were needed to connect them,leading to a high risk of failure. In 1959, the invention of the integrated cir-cuit solved this problem. The transistors weremanufactured directly on the surface of thesilicon, and their connections were made bydepositing metal layers on this surface.There were no further obstacles to the manu-facture of increasingly complex devices, com-bining transistors, diodes, resistors and capa-citors. The very first integrated circuit consistedof six transistors. These devices would continueto be miniaturized and become more dense.

MODERN INTEGRATED CIRCUITS In 2005, a microprocessor (the most complexintegrated circuit) is a piece of silicon plateabout 2.5 square cm. It can contain severalhundred million components. It is known as a“chip" and enclosed in a protective case with"legs" which provide connections with othercomponents of the device in which it operates.Most transistors are MOS (standing for MetalOxide Semiconductor), a technology deve-loped in the 1970s. This enables the manu-facture of transistors that consume less andallows the integration of resistors, another

FROM TRANSISTOR TO INTEGRATED CIRCUITIn 1948, John Bardeen, Walter Brattain andWilliam Shockley, three American physicists,invented the bipolar transistor and in doing soopened up the age of microelectronics. The bipolar transistor consists of an electronemitter, a collector and a modulation deviceknown as a base. The movement of electronsno longer took place in a vacuum but in a solidmaterial, semi-conductors by which the ability

to drive the flow of electrons iscontrolled. Reliability improvedconsiderably.In addition, transistors were morecompact than vacuum tubes.

“With the transistor, electrons movethrough solid material and no longerthrough a vacuum.”

This is madeeither ofgermanium orof dopedmonocrystallinesilicon, forexample.

HOW DOES A MOSTRANSISTOR WORK?

A MOS transistor consists of a sourceand a drain between which electronscan flow via a conductor channel.

This channel acts as a switch,depending on the electric charge ofthe grid.

Depending on the polarity of the grid,the conductor channel is either openor closed.

The performance of the transistordepends mainly on the size of the grid.The smaller this is, the shorter thedistance the electrons have to travel inthe channel and the quicker thesystem.

a few key dates in the history of microelectronics a few key dates

1964First integrated circuit produced by CEA/LETI

1960In the United States, the launchof the Apollo program, with $25billion funding, gives atremendous boost to research oncomputers and integratedcircuits.

1959Jack Kilby and Robert Noyce,two American researchers,produce the first integratedcircuit, consisting of sixtransistors. Most importantly,they solve the problem ofwelding connections, which areproduced by deposition of metallayers on the silicon.

1974The French engineer RolandMoréno invents the smart card.

Technology research laboratory in the 1980s.

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Insulator

Substrate

Insulator

Conductorchannel

Conductor transistor (switch closed)

Grid

Blocked transistor (switch open)

Substrate

Grid

Electron current

a few key dates in the history of microelectronics. a few key dates in

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important component of integrated circuits. The size of integrated circuits regularly increases.The size of the silicon plates on which the circuits are manufactured also increases to maintain the same number of chips on eachplate. Over the past twenty years, the micro-electronics industry has used a successionof silicon ingots: 100 mm in diameter, then200 mm, and then 300 mm.The silicon is not used in pure form: it is "doped"by adding very small quantities of foreign ions

1996The Intel Pentium Pro processoruses 5.5 million transistors. Thiswould be followed in 1999 by theIntel Pentium III (9.5 million) andin 2002 by the Intel Pentium IV(55 million). This compares with2,300 transistors in the first Intelmicroprocessor, the 4004,released in 1971.

1991Michel Bruel, a researcher atCEA/LETI, invents the Improveprocess for Silicon On Insulator(SOI) manufacture, increasingproductivity tenfold. SOI willbecome the key material forproducing fast, energy-efficientcircuits.

2003First industrial production ofchips on silicon wafers 300 mmin diameter.


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TO PRODUCE THE "INFINITELY SMALL" GIGANTIC FACTORIES ARE NEEDED.

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How are How are integrated integrated circuits made?circuits made?

“A modern microprocessor

consists of several billion components on a 2.5 cm square.”

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(arsenic, boron, phosphorus) that guide and facilitate the flow of the current.The circuit can be etched on solid silicon ora thin layer of a few hundred nanometers depo-sited on an insulator. Silicon On Insulator or «SOI»), which can makefaster and more energy-efficient circuits, isincreasingly used. The best manufacturing pro-cess was invented in 1991 by a CEA resear-cher.

THE CLEAN ROOM, AN ULTRAPURE ENVIRONMENTOn the scale of an integrated circuit, a minis-cule dust particle appears like a giant boulderblocking the channels that have been dug outfor the electron flow. This is why productiontakes place in what is known as a clean room.The air is filteredand changed tentimes a minute. It contains 100,000 to 1,000,000 times lessdust than the air outside. Workers always wearoveralls that cover them from head to toe andretain the organic material and dust particlesthat they produce naturally.In addition, many cleaning processes are carried out on the wafers between the stagesof manufacture. In total they account for almosta third of the total processing time.

Despite all these efforts, the number of functional chips on a production line does not

exceed 20% at the launchof a new production facility. The efforts of the

production team will quickly increase this figureto 80% or even 90%.

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A clean roomat LETI,to CEA Grenoble.

INCREASINGLY EXPENSIVE PLANTManufacturing an integrated circuit involves producing a collection of millions of intercon-nected components on a surface a few centi-meters square and a few microns thick, anddoing this for hundreds of identical copiessimultaneously. The more integrated circuits are miniaturized,the more expensive the factories that manu-facture them become. A “fab” (a productionunit) costs roughly the same price as 300 Airbus320s! There are several reasons for this:- The smaller the circuits become, the cleanerthe working environment needs to be to avoidcritically contaminating them. The require-ments for clean rooms are increasingly stringent.- The smaller they become, the more the production machines are accurate, reliable, anddifficult to develop and maintain. In addition, they are only manufactured in smallseries.- The smaller they become, the greater the needfor special materials, technically complex solu-tions and additional manufacturing steps.Today there are around 200 of these per cir-cuit.

“The air in clean rooms contains between100,000 and 1,000,000 times less dust thanthe air outside.”

“The price of a production unit isequivalent to the cost of 300 Airbus A320s.”

A place where the humidity,temperature, water and chemicalsproduced are strictly controlled.

Number of functional chipsproduced as a proportionof the number of chipsmanufactured.

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CAD: TOWNS SCALED DOWN TOCENTIMETER SIZEIt is impossible to design a circuit of severalmillion elements without using a computer:

Every chip designer uses CAD (Computer-aideddesign) to determine the main functions, select themodules in the stored libraries, arrange thesemodules in relation to each other, simulate theoperation, etc. The exercise is long, difficult andincredibly detailed.If you imagine that amicroprocessor with100 million transistorshad a side measuring6 square km (thesurface area of a townof 100,000inhabitants), then eachgrid transistor insulatorwould be only onemillimeter thick!

Production facility of ST Microelectronics, at Crolles (Isère).

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“Mass production of hundreds of copiesreduces the unit cost per chip.”

MASS PRODUCTION, A VITAL ASSETThe base material for the integrated circuit is sili-con, the most widespread chemical element onEarth. It is extracted from sand by reduction,crystallized in the form of bars 20 or 30 cm indiameter, then cut into wafers less than one mil-limeter thick, which are polished to obtainsmooth surfaces of around 0.5 nanometers. Hundreds of chips are produced simultaneouslyon this wafer through the repetition or combina-tion of basic operations, heat treatment, deposition, photolithography, etching, cleaning,polishing and doping. This mass production, which brings down unitcosts, is one of the key assets of the microelec-tronics industry. It explains why microsystemsmanufacturers seek to produce their products withthe selfsame technologies. Yet it also imposesrestrictions on production: a handling error, a fewseconds more or less and several hundred circuits will end in the garbage can...

300 mm silicon bar.

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HEAT TREATMENTCarried out in ovens at temperatures of 400 to1,200°C, it can be used to make layers of oxides,dielectrics to rearrange crystal lattices or toconduct certain doping operations.

PHOTOLITHOGRAPHYThis is a key step and involves repro-ducing the circuit design to becreated in a photosensitive resist. Theresist is deposited on the substrate.The light from a very low wavelengthlight source (UV or lower) projectsthe image via a mask. The higherthe optical resolution, the more theminiaturization of the circuits canbe improved.

ETCHINGIn contrast to deposition, etching removes mate-rial from the wafer, with the aim of producing apattern. There are two main methods: "wet" etching,which uses reactive liquids, and dry (or plasma)etching, which uses reactive gases.

DOPINGTo introduce atoms that will change itsconductivity into the core of the silicon, arerealized by implantation or heated in ovensto between 800 and 1,100°C, in the pre-sence of dopant gas, or bombarded withan accelerated ion beam through a mask.

DEPOSITIONSThese put conductive or insulating layers on thesurface of silicon: oxides, nitrides, silicides,tungsten, aluminum, copper, etc. They are pro-duced by various techniques using gases orliquids: chemical vapor deposition (CVD), phy-sical vapor deposition (PVD), pulverization, epi-taxy, electrodeposition, etc.

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THE BASIC OPERATIONS

CHEMICAL MECHANICALPOLISHING (CMP)

This basic step combines a mechanical rota-tional motion and a chemical effect in orderto planarize the surface of the wafer and toimprove its quality. To do so, a part of mate-rial is removed. This technique, used severaltimes during the integration, improves alsothe performance of the photolithographywitch is realized on a flat surface.

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“TOP DOWN“ AND “BOTTOM UP”The advent of nanotechnology brings with ittechnical challenges so ambitious that theycould act as a brick wall against the powerfulstream of innovation that runs through theindustry. How can we etch lines that are onlya few nanometers thick? How can we effecti-vely insulate electrical tracks with materials nomore than a few atomic layers thick? How canwe make transistors through which only a hand-ful of electrons can pass? Two approaches are being pursued in parallelto overcome these obstacles:- The top downapproach: this involves pushingto the limit the extreme miniaturization of theMOS transistor, continuing the work of thepast 40 years;- The bottom upapproach: this instead involvesassembling the material atom by atom, to buildmolecules that are then joined in transistorswith a completely new design. This approachmakes use of basic knowledge of physics and

AT THE CROSSROADS OF PHYSICS AND CHEMISTRY, A NEW CHALLENGE FOR MICROELECTRONICS ISEMERGING, BRINGING WITH IT DISCOVERIES, APPLICA-TIONS AND JOBS.

chemistry, disciplines to which microelectro-nics should open up.

THE WAY FORWARD FOR NANOTECHNOLOGIESIn another major development, microelectro-nics will interfere more and more with the worldof micro and nanosystems: accelerometers forairbags, clothing that can communicate,camera capsules to introduce a micro-camerainto the body, biochips for biological analysis,laboratory chip analysis, etc.

These devices combine sensors and chips,which are essential for processing the datagathered. Their production will necessarily callfor nanoelectronic technologies to meet minia-turization and cost objectives. We are at another cultural and disciplinary crossroads,namely between electronics and micro andnano-level systems.

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“It is now possible to assemble the materialatom by atom, to build transistors with acompletely new design.”

Biochip LabPM.

Nanofils.

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NanoelectronicsNanoelectronics

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