Microelectronics

w From the electron to ch>ip I NmTaRnOufDaUctCuTrIiOnN g THE COLLECTION

1 w The atom 2 w Radioactivity 3 w Radiation and man 4 w Energy 5 w Nuclear energy: fusion and fission 6 w How a nuclear reactor works FROM RESEARCH 7 w The nuclear fuel cycle 7 w The nuclear fuel cycle TO IINDUSTRY 8 w Microelectronics 9 w The laser: a concentrate of light 10 w Medical imaging 11 w Nuclear astrophysics 12 w Hydrogen 13 w The Sun 14 w Radioactive waste 15 w The climate 16 w Numerical simulation 17 w Earthquakes 18 w The nanoworld

8 w MMiiccrrooeelleeccttrroonniiccss

A TECHNOLOGICAL REVOLUTION A BRIEF HISTORY HOW ARE INTEGRATED CIRCUITS MADE? NANOELECTRONICS

ISSN 1637-5408.

De l’électron à la fabrication des puces 8 > La microélectronique De l’électron à la fabrication des puces 8 > La microélectronique 2 > CONTENTS w> INTRODUCTION 3

Microelectronics enables new applications on account of its miniaturization and high performance. For example in A E C

/ medicine with this a p

p DNA-chip o r t S

. (on the right) P

A TECHNOLOGICAL becoming more powerful and cheaper, go

s REVOLUTION 4 on being miniaturized?” Making microelectronics

c more widely accessible 5 i More complex calculations 6 Innovative products n and services 7 o A E C A BRIEF HISTORY... 8 / introduction a r p p o r

The diode, the key electroni c t S t

. ell phones, digital cameras, MP3 players, PCs, P device 9 © games consoles, bank cards, cars: in just a Yet the outlook for the microelectronics industry c C From transistor to integrated Observation of a silicon wafer using an optical microscope. circuit 10 few decades, integrated circuits or "chips" have is far from clear. Transistors will soon become

e Modern integrated circuits 11 taken over most of the things we use everyday. so small that they will be extremely difficult

l This takeover is unprecedented in the history of to manufacture and operate. For example, the HOW ARE INTEGRATED technology. It reflects the accelerated pace of thickness of some (oxide) insulators may be e CIRCUITS MADE? 13 innovation in the microelectronics industry, no greater than 1 nm, that is, 3 or 4 oxide which has gone on producing ever smaller tran - atomic layers!

o Increasingly expensive plants 14 sistors, resulting in turn in more powerful and Industry, research laboratories and institutes r The clean room, an ultra pure efficient integrated circuits. are setting in place research programs backed

c environment 15 In 1971, the Intel 4004 processor contained by heavy investment. This is especially the case

i Mass production 16 approximately 2,300 transistors. In 2006, the in the Grenoble region, a world-class center Basic operations 17 prospect emerged of chips with a billion tran - for microelectronics. It is home to the CEA’s sistors. This amazing yet compact intelligence LETI (Laboratory of Electronics and Informa - M NANOELECTRONICS 18 is becoming cheaper and cheaper: in 1973, it tion Technology) and ST Microelectronics manu - Top down and bottom up 19 cost the price of an apartment to manufacture facturing in Crolles site combine forces. Finally, The way forward for nano - a million transistors; today it costs the price of 4,000 people have been working in Grenoble technologies 19 a post-it. since 1976 at Minatec, the leading European innovation cluster for micro and nanotechno - logies.

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 From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 4 w A TECHNOLOGICAL REVOLUTION 5

40 YEARS OF CONTINUOUS PROGRESS AND “On a 45 nm printed circuit the etchings NEW PRODUCTS AND SERVICES LIE BEHIND are a thousand times thinner than a THE AGE OF MINIATURIZATION . hair.” AA tteecchhnnoollooggiiccaall MAKING MICROELECTRONICS In order to maintain this pace of development, MORE WIDELY ACCESSIBLE we must constantly call into question: the mate - Microelectronics is not an established and rials used for circuits, electrical connections rreevvoolluuttiioonn stabilized business. The number of transistors and insulators; circuit architectures, which per unit area quadruples every three years and represent a decisive factor in the final perfor - the cost of the circuits halves every 18 months, mance; production equipment, some of it particularly through mass production of hun - costing several million euros; the size of the dreds of chips on each silicon wafer. silicon wafers on which circuits are produced This growth curve in performance was (200 mm and 300 mm), along with all the described in 1965 by Gordon Moore, cofounder methods used in their manufacture. of Intel Corporation. It has proven so accurate To attain this level of performance, the most that it is now known as "Moore's law" by all the significant factor is how thin the etchings are. manufacturers in the sector, who rely upon it Initially this was expressed in This technic define to plan their investments and research programs microns (millionths of a meter): the width of the patterns molded on years in advance. 0.25 micron, then 0.18 micron, the silicon.

MOORE LAW chip A E C / t e r u D

s i n e D

“The power of current supercomputers can reach INTERNAL DESIGN OF AN MP3 PLAYER Microprocessor 1,000 billion operations per second... thanks to Controls the operating system and software advances in microelectronics .” A E C

© Flash memory Analog-digital A way of storing music converter without using power and then 0.13 micron. Since the turn of the performance reaches the teraflop. century, the most commonly used unit is now Advances in integrated cir - 1,000 billion operations per second. the nanometer (a billionth of a meter). A pro - cuits are the cause of this duction facility like Crolles produces 45 nm cir - giant leap, which has opened new possibilities: USB flash drive Controls and encodes the Keyboard and display cuits or etchings a thousand times finer than - The design of complex systems or products. connection with the computer Computer Display and data retrieval, user interface the thickness of a hair. This can be done entirely on computer. Depen - Manages the coding and decoding of sound using psychoacoustic These technological achievements have led to ding on the expected conditions of use, the com - algorithms a fall in costs, an increased level of performance puter calculates the behavior of the materials, and more widespread use of microelectronics, the dimensions of the components, and their with two consequences: constantly increasing spatial layout, and then draws the plans. ©Philips computer power and new products and services - Phenomenological modeling. The behavior of for the general public. an airliner in turbulence or five-day changes in the weather depend on a whole host of para - in-flight behavior. In design terms, computer be used to make telephone calls. The latest MORE COMPLEX COMPUTATION meters. They can be modeled, that is repre - simulation allows an engine to be tested, for models are ultra-lightweight and feature games, FOR DESIGN, SIMULATION AND sented by a series of complex operations whose example, before producing a prototype, to see HD cameras, and Internet connection for the MODELING... result is very close to the actual phenomenon. how it will be affected by heating, road vibra - same price or less. Post-war scientists carried out their calcula - - Computer simulation. This time the process tions or shocks. Finally, it should be borne in mind that most tions on computers that occupied entire rooms, involves "manipulating" the models. For example, such equipment includes not one but several and whose performance was no greater than by providing the weight of the aircraft and its INNOVATIVE PRODUCTS AND integrated circuits (microprocessors and that of a modern calculator. Early twenty-first speed, plus the strength and direction of the SERVICES memory) that have been carefully designed to century scientists have supercomputers whose turbulence, the computer can then predict its The computing power of integrated circuits can work together and enhance the overall perfor - offer the general public high-performance, mance of the device. user-friendly equipment, with a whole range of features: cell phones, DVD players, digital televisions, MP3 players, digital cameras, bank cards, and so on. The chips power both the computing functions and the interfaces (such “The most successful as the keyboard, display, and USB) that make consumer products them intuitive and easy to use. Moreover, the size and price of the products have more features, A

E are steadily decreasing. The consumer is the

C are more compact,

n winner on all fronts. The cell phone provides o p

u and cheaper.” D

a perfect illustration of this phenomenon. The R . C D

From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 8 w A BRIEF HISTORY... 9 INACENTURY , MINIATURIZATION HAS ENABLED 1904 1948 1954 THE TRANSITION FROM THE VACUUM TUBE TO John Alexander Fleming, an John Bardeen, Walter Brattain and Texas Instruments manufacture the English engineer, invents the William Shockley, three physicists first silicon transistor. They were diode. This was the first electronic at the Bell Laboratories (USA), the size of dice, but within a THE ONE -MICROMETER -SQUARE TRANSISTOR . device and was used in radio produce the first transistor. decade would be as small as a receivers. In 1907, Lee de Forest, Reliability, smaller size, reduced grain of salt. However, the vast an American researcher, develops power consumption: the route to number of connecting threads the principle further by inventing miniaturization opens up. This holds back the development of the triode. major discovery would win them complex circuits. a few key date sthe iNnob etlh Periz eh foirs Phtyosircsy in of microelectronics a few key AA bbrriieeff hhiissttoorryy...... 1956. THE DIODE, THE KEY ELECTRONIC DEVICE The history of electronics began in 1904 with the invention of the diode, used in radio sets. R D

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 changed in order to make or break the flow of current. In 1907 the triode appeared, in which a grid is added between the filament and the plate. This grid acts as a modulator of the electrons: depending on its polarization, it either blocks them or makes them flow faster (current ampli - A E

fication). C

During the 1940s, triodes and other types of © Vacuum diodes and transistors from 1965 (above). valves were used in the first electronic compu - ters capable of performing calculations faster complex calculations such as those required by than a human being. The numbers and tasks physicists, the number of vacuum tubes needs were coded in binary, using 0 or 1. For instance, to be multiplied, and they are bulky, produce 1 corresponds to the flow of electrical current, lots of heat and “fail” easily. This lack of relia - 0 to it being stopped. However, to carry out bility held back the development of computing.

WHERE DOES THE WORD “BUG” COME FROM?

The English word bug usually denotes an insect or These were all the more numerous because ENIAC "creepy crawly". So then how is this connected with the was a 30-ton monster, occupying 72 square m and bugs in software? It is quite simple. With ENIAC, the using more than 17,000 vacuum tubes. world’s first computer, developed at the University of This was how bugs came to be part of the world of Pennsylvania in 1946, a major cause of failure was computing… e

u small butterflies landing on electrical connections. q i n h c e t r A

© From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 10 w A BRIEF HISTORY... w A BRIEF HISTORY... 11 1959 1960 1964 1974 Jack Kilby and Robert Noyce, In the United States, the launch First integrated circuit produced The French engineer Roland “With the transistor, electrons move two American researchers, of the Apollo program, with $25 by CEA/LETI Moréno invents the smart card. produce the first integrated billion funding, gives a through solid material and no longer circuit, consisting of six tremendous boost to research on transistors. Most importantly, computers and integrated A E

they solve the problem of circuits. A through a vacuum.” C

E © C

welding connections, which are produced by deposition of metal © layers on the silicon. a few key dates in the history of microelectronics a few key dates

FROM TRANSISTOR TO Within a few years, they went from being the INTEGRATED CIRCUIT size of dice to the size of a grain of salt! In 1948, John Bardeen, Walter Brattain and The transistor was used in new radio sets - to William Shockley, three American physicists, which it gave its name - and in computers. invented the bipolar transistor and in doing so Yet another obstacle quickly became apparent: opened up the age of microelectronics. the more transistors there were, the more welded The bipolar transistor consists of an electron copper threads were needed to connect them, emitter, a collector and a modulation device leading to a high risk of failure. HOW DOES A MOS Insulator known as a base. The movement of electrons In 1959, the invention of the integrated cir - Electron current no longer took place in a vacuum but in a solid cuit solved this problem. The transistors were TRANSISTOR WORK?

material, semi-conductors by which the ability manufactured directly on the surface of the d A MOS transistor consists of a source Gri This is made to drive the flow of electrons is silicon, and their connections were made by and a drain between which electrons either of controlled. Reliability improved depositing metal layers on this surface. can flow via a conductor channel. germanium or Substrate of doped considerably. There were no further obstacles to the manu - This channel acts as a switch, Conductor monocrystalline In addition, transistors were more facture of increasingly complex devices, com - depending on the electric charge of channel silicon, for example. compact than vacuum tubes. bining transistors, diodes, resistors and capa - the grid. citors. The very first integrated circuit consisted Conductor transistor (switch closed) of six transistors. These devices would continue Depending on the polarity of the grid, to be miniaturized and become more dense. the conductor channel is either open or closed.

MODERN INTEGRATED CIRCUITS The performance of the transistor Insulator In 2005, a microprocessor (the most complex depends mainly on the size of the grid. integrated circuit) is a piece of silicon plate The smaller this is, the shorter the Grid about 2.5 square cm. It can contain several distance the electrons have to travel in the channel and the quicker the hundred million components. It is known as a system. Substrate “chip" and enclosed in a protective case with "legs" which provide connections with other components of the device in which it operates . Most transistors are MOS (standing for Metal Blocked transistor (switch open) Oxide Semiconductor), a technology deve - loped in the 1970s. This enables the manu - R D

From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 12 w A BRIEF HISTORY... 13 1991 1996 2003 TO PRODUCE THE "INFINITELY SMALL " Michel Bruel, a researcher at The Intel Pentium Pro processor First industrial production of GIGANTIC FACTORIES ARE NEEDED CEA/LETI, invents the Improve uses 5.5 million transistors. This chips on silicon wafers 300 mm . process for Silicon On Insulator would be followed in 1999 by the in diameter. (SOI) manufacture, increasing Intel Pentium III (9.5 million) and productivity tenfold. SOI will in 2002 by the Intel Pentium IV become the key material for (55 million). This compares with producing fast, energy-efficient 2,300 transistors in the first Intel circuits. microprocessor, the 4004, released in 1971. a few key dates in the history of microelectronics. a few key dates in HHooww aarree

important component of integrated circuits. (arsenic, boron, phosphorus) that guide and iinntteeggrraatteedd The size of integrated circuits regularly increases. facilitate the flow of the current. The size of the silicon plates on which the The circuit can be etched on solid silicon or circuits are manufactured also increases to a thin layer of a few hundred nanometers depo - maintain the same number of chips on each sited on an insulator. circuits made? plate. Over the past twenty years, the micro- Silicon On Insulator or «SOI» ), which can make circuits made? electronics industry has used a succession faster and more energy-efficient circuits, is of silicon ingots: 100 mm in diameter, then increasingly used. The best manufacturing pro - 200 mm, and then 300 mm. cess was invented in 1991 by a CEA resear - The silicon is not used in pure form: it is "doped" cher. by adding very small quantities of foreign ions

“A modern microprocessor consists of several billion components on a 2.5 cm square.” A E C

a p A p E o C r

t S ©

. P

© From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 14 w HOW ARE INTEGRATED CIRCUITS MADE? w HOW ARE INTEGRATED CIRCUITS MADE? 15

“The air in clean rooms contains between 100,000 and 1,000,000 times less dust than the air outside.”

INCREASINGLY EXPENSIVE PLANT THE CLEAN ROOM, AN ULTRA Manufacturing an integrated circuit involves PURE ENVIRONMENT CAD: TOWNS SCALED DOWN TO producing a collection of millions of intercon - On the scale of an integrated circuit, a minis - CENTIMETER SIZE nected components on a surface a few centi - cule dust particle appears like a giant boulder It is impossible to design a circuit of several meters square and a few microns thick, and blocking the channels that have been dug out million elements without using a computer: doing this for hundreds of identical copies for the electron flow. This is why production Every chip designer uses CAD (Computer-aided design) to determine the main functions, select the simultaneously. takes place in what is known as a clean room . modules in the stored libraries, arrange these The more integrated circuits are miniaturized, The air is filtered A place where the humidity, modules in relation to each other, simulate the the more expensive the factories that manu - and changed ten temperature, water and chemicals operation, etc. The exercise is long, difficult and produced are strictly controlled. facture them become. A “fab” (a production times a minute. incredibly detailed. If you imagine that a unit) costs roughly the same price as 300 Airbus It contains 100,000 to 1,000,000 times less microprocessor with 320s! There are several reasons for this: dust than the air outside. Workers always wear 100 million transistors - The smaller the circuits become, the cleaner overalls that cover them from head to toe and had a side measuring the working environment needs to be to avoid retain the organic material and dust particles 6 square km (the surface area of a town critically contaminating them. The require - that they produce naturally. of 100,000 ments for clean rooms are increasingly In addition, many cleaning processes are inhabitants), then each R D stringent. carried out on the wafers between the stages grid transistor insulator © would be only one - The smaller they become, the more the Production facility of ST Microelectronics, at Crolles (Isère). of manufacture. In total they account for almost production machines are accurate, reliable, and a third of the total processing time. millimeter thick! difficult to develop and maintain. In addition, they are only manufactured in small Despite all these efforts, the number of series. functional chips on a production line does not - The smaller they become, the greater the need Number of functional chips exceed 20% at the launch produced as a proportion for special materials, technically complex solu - of the number of chips of a new production tions and additional manufacturing steps. manufactured. facility. The efforts of the Today there are around 200 of these per cir - production team will quickly increase this figure cuit. to 80% or even 90%.

“The price of a production unit is A E C

/ equivalent to the cost of a p p

o A clean room r t S

300 Airbus A320s.” . at LETI, P

From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 16 w HOW ARE INTEGRATED CIRCUITS MADE? w HOW ARE INTEGRATED CIRCUITS MADE? 17

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

THE BASIC OPERATIONS 1 HEAT TREATMENT 4 ETCHING Carried out in ovens at temperatures of 400 to In contrast to deposition, etching removes mate - 1,200°C, it can be used to make layers of oxides, rial from the wafer, with the aim of producing a dielectrics to rearrange crystal lattices or to pattern. There are two main methods: "wet" etching, conduct certain doping operations. which uses reactive liquids, and dry (or plasma) R D

MASS PRODUCTION, These put conductive or insulating layers on the © P. Stroppa / CEA A VITAL ASSET surface of silicon: oxides, nitrides, silicides, 5 CHEMICAL MECHANICAL The base material for the integrated circuit is sili - tungsten, aluminum, copper, etc. They are pro - POLISHING (CMP) con, the most widespread chemical element on duced by various techniques using gases or Earth. It is extracted from sand by reduction, liquids: chemical vapor deposition (CVD), phy - This basic step combines a mechanical rota - crystallized in the form of bars 20 or 30 cm in sical vapor deposition (PVD), pulverization, epi - tional motion and a chemical effect in order diameter, then cut into wafers less than one mil - taxy, electrodeposition, etc. to planarize the surface of the wafer and to improve its quality. To do so, a part of mate - limeter thick, which are polished to obtain © P. Stroppa / CEA rial is removed. This technique, used several smooth surfaces of around 0.5 nanometers. © D 3 PHOTOLITHOGRAPHY times during the integration, improves also R Hundreds of chips are produced simultaneously the performance of the photolithography on this wafer through the repetition or combina - This is a key step and involves repro - witch is realized on a flat surface. tion of basic operations, heat treatment, ducing the circuit design to be deposition, photolithography, etching, cleaning, created in a photosensitive resist. The polishing and doping. resist is deposited on the substrate. 6 DOPING This mass production, which brings down unit The light from a very low wavelength To introduce atoms that will change its costs, is one of the key assets of the microelec - light source (UV or lower) projects conductivity into the core of the silicon, are tronics industry. It explains why microsystems the image via a mask. The higher realized by implantation or heated in ovens manufacturers seek to produce their products with the optical resolution, the more the © Artechnique/CEA to between 800 and 1,100°C, in the pre - the selfsame technologies. Yet it also imposes miniaturization of the circuits can sence of dopant gas, or bombarded with restrictions on production: a handling error, a few be improved. an accelerated ion beam through a mask. seconds more or less and several hundred © P. Stroppa / CEA circuits will end in the garbage can...

From the electron to chip manufacturing 8 w Microelectronics From the electron to chip manufacturing 8 w Microelectronics 18 w NANOELECTRONICS 19 AT THE CROSSROADS OF PHYSICS AND CHEMISTRY , A NEW CHALLENGE FOR MICROELECTRONICS IS “It is now possible to assemble the material EMERGING , BRINGING WITH IT DISCOVERIES , APPLICA - atom by atom, to build transistors with a TIONS AND JOBS . completely new design.”

NNaannooeelleeccttrroonniiccss chemistry, disciplines to which microelectro - “TOP DOWN“ AND “BOTTOM UP” nics should open up. The advent of nanotechnology brings with it technical challenges so ambitious that they THE WAY FORWARD FOR could act as a brick wall against the powerful NANOTECHNOLOGIES stream of innovation that runs through the In another major development, microelectro - industry. How can we etch lines that are only nics will interfere more and more with the world a few nanometers thick? How can we effecti - of micro and nanosystems: accelerometers for vely insulate electrical tracks with materials no airbags, clothing that can communicate, more than a few atomic layers thick? How can camera capsules to introduce a micro-camera we make transistors through which only a hand - into the body, biochips for biological analysis, ful of electrons can pass? laboratory chip analysis, etc. Two approaches are being pursued in parallel to overcome these obstacles: - The top down approach: this involves pushing to the limit the extreme miniaturization of the MOS transistor, continuing the work of the past 40 years; - The bottom up approach: this instead involves assembling the material atom by atom, to build molecules that are then joined in transistors with a completely new design. This approach makes use of basic knowledge of physics and A E C

These devices combine sensors and chips, which are essential for processing the data gathered. Their production will necessarily call for nanoelectronic technologies to meet minia - turization and cost objectives. We are at A

E another cultural and disciplinary crossroads, C / A A e E E u C C

t Nanofils. nano-level systems. r A