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The Exploitation of Semiconductors
ADVANCES IN IMAGING AND ELECTRON PHYSICS,VOL. 91
The Exploitation of Semiconductors B. L. H. WILSON Armada House, Weston, Towcesler, United Kingdom
. . . . . . . . . . . . . . Technology . . . . . . . . . . . . The Transistor . . . . . . . . . . . A. Competition between Transistor Types . . B. The Diffused Transistor . . . . . . . C. The Planar Transistor . . . . . . . . D. Discrete Transistors in the Mid-1960s . . . Integrated Circuits . . . . . . . . . . A. Planar Integrated Circuits . . . . . . B. The New Situation . . . . . . . . .
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This paper covers the discovery of the useful properties of semiconductors, and concentrates very largely on silicon integrated circuits, “chips,” whose social and economic importance far transcends the very substantial influence of other semiconductors. An accompanying paper covers gallium arsenide. It is written from the standpoint of the United Kingdom, and attempts to show how the U.K.’s substantial contribution to the early development of silicon ICs has not led to a large industry in the indigenous companies, though there is a substantial industry which manufactures chips on processes developed elsewhere, sustained by inward investment. Some reasons are suggested for this failure. The paper is written from the point of view of someone closely associated with the IC development in Plessey, which was one of the leading companies in U.K. integrated circuit development for nearly 30 years. As such, it does not explicitly recognize the substantial contributions made by many other U.K. companies, such as Phillips, S.T.C., G.E.C., Ferranti, and Inmos. 141
Copyright 0 1995 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-014733-5
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I. PREHISTORY
The first observation of semiconducting properties is sometimes said to be the observation of Faraday of the negative temperature coefficient of resistance in silver sulfide in 1835. Two years later, Rochenfeld was the first to observe rectifying contacts. Although there were many relevant observations throughout the 19th century, particularly of photoconductivity, we will now skip to the early days of radio, where point contact rectifiers on various semiconductors were found to be efficient detectors in the period 1902-1906 (Bose, Pierce); Pickard observed that silicon was among these materials. Though cat’s whiskers became familiar to many until they were largely supplanted by valves, no real scientific development occurred until the Second World War. In the meantime, a substantial semiconductor industry had sprung up to expoit the rectifying properties of copper oxide and selenium, the first selenium rectifiers being produced commercially in 1927. There were, however, a number of anticipations of the (field-effect) transistor between the wars by Lilienfeld and others in the 1920s. The first published scientific account of a device that actually worked was by Hilsch and Pohl in 1935. The geometry of their “transistor” was such that gain could only be obtained below 1 Hz. Some of the early inventors had hit on the correct principle, that charge induced on the opposite plate of a capacitor could be mobile and give current between what we should now call source and drain. They failed to appreciate how easily it could be trapped at surface or interface states. 11. THECONCEPTUAL FRAMEWORK
It is unlikely that any substantial technology could have emerged before an adequate scientific framework had been put in place. The quantum theory of metals was first developed by Sommerfeld and Bloch in 1928, and this was followed by Wilson’s paper on the quantum theory of semiconductors in 1932. It developed a theory of electron and hole conduction in terms of contributions by impurities, which had respectively one more or one less electron than the host semiconductor. Wilson, an Englishman, later published a substantial book on the theory of metals (and semiconductors), which still seems surprisingly modern. He subsequently went into metallurgy as a business and was remarkably successful. At that time, no-one in the West was thinking about what might happen if both electron conduction and hole conduction were present in different parts of the same semiconductor. The Russian physicist Davydov published his theoretical paper
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in 1938 on the properties of such p-n junctions, including minority carrier injection, but despite the fact that the paper was available in English translation, it required the stimulus of the war for practical demonstration. 111. TECHNOLOGY
The development of radar during the war provided the incentive for a new investigation of the point contact diode detector at what were then felt to be high frequencies. B.T.H. at Rugby contributed notably to the British work, but much the largest and most widely distributed effort took place in the U.S.A., notably at Bell and Purdue. This included the development of techniques for the chemical control of purity of germanium and silicon, the preparation of polycrystalline material, and developments in sawing, polishing, and etching. p-n junctions were studied by Oh1 in 1941. Remarkably, the importance of single-crystal growth was not realized, and even when Teal and Little grew the first germanium crystals in 1948, it was without the support of their laboratory head, Shockley, who led the Bell laboratories team. Subsequently, Teal left Bell for Texas Instruments, where he succeeded in growing single crystals of silicon, providing a technical boost to Texas’s capability in what was destined t o be the most important semiconductor. IV. THETRANSISTOR As is well known, the first transistor was invented by Bardeen and Brittain in 1947, though the invention was not disclosed until 1948. They were
members of a team at Bell laboratories doing fundamental work on semiconductors, in this instance the study of surface states. To probe the surface, a second point electrode was brought down close to the point of a point contact rectifier, and it was realized that under appropriate circumstances the second wire could act as a control electrode for the current injected from the first. The importance of the discovery was rapidly realized, even though the early transistors were unstable and noisy. During the period 1948-1951, Shockley developed the p-n junction transistor, which overcame many of the early problems. The invention commanded worldwide attention: The prospects of a device without the large bulk, complexity, unreliability, large power drain, and limited life of the valve were quickly realized.
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A . Competition between Transistor Types
An early type of junction transistor t o emerge was the alloy transistor (1950). A thin die or chip of semiconductor, almost always germanium, had fired into its two opposing faces small beads of metal, typically indium. As the molten metal cooled down, dissolved germanium grew in the pits which the molten metal had etched. The regrown regions were doped with indium, and the resultant structure was a p-n-p alloy transistor. Although production required complex jigs made from carbon or steel, and not many transistors were made in a batch, it was comparitively simple, and the process was copied and licensed very widely. More transistors could be made simultaneously if the transistor structure was made during growth of the original crystal, by overdoping the original doping with an impurity of opposite type added to the melt, and then overdoping again. The region with transistor structures was cut from the grown crystal as a thick disk, which was in turn cut up into a large number of long cuboids, which formed the transistor. Although many transistors were formed simultaneously, it was necessary to grow a whole crystal to form them; this grown junction process (1951) was thus extremely uneconomical in material. Furthermore, it was hard to make contact with the narrow base region, and this early type soon became obsolete. A problem with the alloy transistor was that the emitter and collector electrodes were separated by a thickness comparable with that of the original wafer. The frequency response of the transistor was limited by the time it took for minority carriers to diffuse across this distance, several tens of microns, and could not extend much above the audio range. To solve this problem, Philco introduced the electrochemical transistor, in which an individual transistor die was mounted on a special jig so that dimples could be electrochemically etched on both sides, leaving in the transistor region only a thin web of germanium whose thickness could be monitored by its transparency. By reversing the polarity, metals could be plated onto both sides, and these could be fired in to form an alloyed transistor. Frequency responses in the megahertz region were now available. Again the process was widely licensed, though its successful deployment was to be short. Another competing type was successfully developed by Philips from the alloy transistor geometry. The doping type of the alloy dots was now of the same type as the germanium wafer, but the collector metal dot contained a second impurity of opposite type. This impurity was selected because it diffused rapidly from the alloy, producing a thin diffused base region, whose thickness was controlled by time and temperature rather than by jigging.
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Although these processes produced a substantial industry and made possible portable radios much superior to the valve radio, they suffered from a number of disadvantages. The production required complex jigs which produced only a limited number of transistors; the electrochemical process required a jig for each transistor. Lead attachment and heat sinking were often problems. The transistors were only suitable for use at ordinary temperatures and could scarcely operate above about 75 "C. Later, silicon variants on these types were introduced, which encouraged military use. Further, the exposed semiconductor surface was extremely sensitive to ambient gases, particularly water vapor. Transistors could not be vacuumencapsulated, but were mounted in sealed cans. Some secrecy surrounded formulations for statisfactory surface treatments, but even the best devices had a limited operating life of some tens of thousands of hours.
B. The Diffused Transistor Some of these disadvantages were overcome in the early diffused transistor in silicon (1956). A whole wafer was subject to two diffusion processes. The first, boron, diffusion produced a thin p-type skin over the whole of the wafer, while the second, phosphorus, diffusion covered it with an even thinner n-type skin to give an n-p-n sandwich. The geometry of the transistor was defined by a photographic process. Originally, wax was used as a mask, but this was soon abandoned. Metal was evaporated onto the whole wafer, which was then covered with photoresist. The photoresist was exposed through a photographic mask and developed so that the wafer was covered by exposed circular islands of resist. The wafer was then etched through the diffused regions of the silicon to produce structures reminiscent of the mesas of Arizona, after which the type was named. A similar step, but with a new mask and lighter etch, exposed the p-type layer for contacting, over part of the original mesa. This process, of which there were a number of variants, had several advantages. A large number of identical high-frequency structures were produced simultaneously, and much of the complex jigging was replaced by a photographic process. This was to prove of decisive importance in reducing costs, particularly when a new variant was invented which eventually solved the stability problem.
C. The Planar Transistor The planar process, which in its developed form is attributed to Hoerni at Fairchild between 1959 and 1961, made use of a process step called oxide masking. Before diffusion, the silicon wafer is thermally oxidized so that it
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is covered with an adherent layer of silica. Resist is then spun over the wafer, and exposed through a photographic mask. The resist is developed to reveal a pattern of holes in the resist, and the wafer is then dipped in hydrofluoric acid to locally dissolve the silica. After removing the resist, the wafer is placed in an oxidizing furnace for the boron diffusion. The silica masks the boron diffusion except where holes had been etched. The boron diffuses down into the wafer and for a similar distance sideways under the silica, so that the p-n junction so formed is protected by a layer of oxide. Oxide also grows over the diffused region in the oxidizing ambient of the diffusion furnace. The process is repeated using a second mask with smaller holes for the emitter diffusion of phosphorus, giving a localized diffused region aligned to the original transistor bases. Finally, metal stripes are evaporated, being again defined by photographic masks. The wafer is sawn into a large number of identical dice, which are subject to a mounting and lead attachment process that could be rapidly performed manually with suitable jigs and was later automated. This process produced very reliable high-frequency transistors, with a temperature range suitable for military and professional use, but in other applications had to compete with established alloy processes. As the collector region could be gold soldered on to a metal carrier, power transistors were also easily made.
D. Discrete Transistors in the Mid-1960s The mid-1960s saw many firms engaged in transistor manufacture in the U.S.A., Europe and Japan. Competition and the resultant price erosion was such that manufacture was not always profitable. In addition, there was competition between transistor types. Manufacturers which had licensed processes for transistor manufacture found that they became obsolescent, and unless this license was merely to back up their own in-house R & D, a new license must be bought as the process became obsolescent. Germanium, despite its shortcomings, was still dominant in volume. However, most large electronics firms felt that this was a technology that they could not afford to neglect, so radical was its influence becoming in key consumer markets, in defence, telecommunications, and computing. This thinking was to be transformed by the rise of the integrated circuit. V . INTEGRATED CIRCUITS
The idea of the integrated circuit was first put forward by a British defense engineer, G . W. A. Dummer, at a meeting of the American I.R.E. in 1952.
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The conception was that a number of components were to be fabricated in a solid block of material, the “solid circuit.” Some years elapsed before this vision could be interpreted. The driving force at the time was “miniaturization” for military purposes. There were two approaches. One was to build up, on a passive substrate such as glass, successive layers of deposited material: gold for interconnections, evaporated nichrome for resistors, and evaporated silicon monoxide for dielectric were commonly used. To these were added active diodes and transistors, often in chip form. This approach was initially easier. Simple metal masks or, later, screen printing were used to differentiate patterns in the various layers. The technique still survives, but did not go on to form a major industry. The more radical approach, the one that best approximated the original solid circuit vision, was to form all the components in a semiconductor chip in what was now to be called an integrated circuit. The first demonstration of the technique was by Jack Kilby of Texas Instruments, who created a multivibrator circuit entirely from silicon in 1958 (announced 1959), albeit connected by a bird’s nest of wires. Serious work in the U.K. began later that year at Plessey’s Caswell laboratories. However, the rise of the planar process was to transform the subject. A. Planar Integrated Circuits
The planar process with its photographic basis and its use of whole silicon wafers and passivated junctions was ideal for extension as the basis of integrated circuit technology. Resistors could be formed from the base diffusion, which was of quite high sheet resistance (200 ohms). By altering the mask pattern, resistors of a desired value could be defined. Although these resistors were temperature-dependent, in many circuits it was the ratio of resistance that mattered, and this was independent of the sheet resistance. The emitter diffusion was of low sheet resistance and could form one plate of a capacitor of which the thermally grown silica was the dielectric and the aluminum metallization was the other plate. The aluminum also formed the main interconnect between components, though cross-overs could be effected by using the emitter diffusion. However, all these components were unfortunately interconnected by the use of a common substrate. Some early circuit designs even attempted to overcome this limitation by cutting holes in the substate. In 1959, Lehovic invented a way to use the reverse-biased p-n junction to isolate the components. The idea was to place each component or group of components on a “land” of n-type material, but to surround that land by a wall of p-type material which was allowed to float with no applied bias.
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No net current could flow into the wall, so what little current did flow was a combination of the small leakage current from reverse bias for the majority of the junction with a compensating current from slightly forward bias of the remainder. Several ways of realizing this isolation compatible with the then-dominant bipolar transistor process were invented. One of the simplest was to use ap-type substrate on which a thin layer of n-type silicon could be grown by the newly invented process of vapor phase epitaxy. The lands for the components could then be formed by a deep diffusion of boron from the surface down t o the p-type substrate. Components could then be made on these lands in the way indicated earlier. More sophisticated versions of the process involved diffusion of the substrate prior to epitaxy: An n-type diffusion which was to appear beneath the transistor collector made the area of the collector an equipotential, while a p-type diffusion coincident with the later deep diffusion eased the demand for vertical penetration of the deep diffusion.
B. The New Situation This invention was to have revolutionary implications for electronic economics, though they were only slowly appreciated, particularly outside the integrated circuit industry. All components, transistors, diodes, resistors, and capacitors were defined by photolithography simultaneously. The cost of processing a wafer was the same irrespective of the complexity it contained. So at high yield the cost of each integrated circuit chip was proportional to its area. So smaller components, i.e., transistors and diodes, were cheaper than area-demanding resistors and capacitors, reversing the usual constraints. Circuits were fully designed before fabrication, as breadboarding was no longer desirable or even possible. A new breed of electronic engineer was required, the integrated circuit designer, who later was to be aided by sophisticated tools for layout, circuit analysis, and synthesis. Yields of integrated circuits were low at first, particularly for complex large-area chips, which suffered most from the defects often associated with dust. This led to the use of expensive clean rooms and protective clothing, filtered air, pure reagents and deionized water, which added greatly to costs. To pack more circuits into the wafer, it was desirable to shrink the size of features on the wafer; this also led to higher-frequency circuits largely because of a reduction in stray junction capacitance. Although the finer lithography required more expensive equipment, the main effect was to give cheaper, and potentially more complex, chips. The situation is often illustrated by the complexity of memory chips, which has risen exponentially from 1 kbit in 1968 to 16Mbits today (1992). Most of this 16-thousand-fold increase is associated with a decrease in feature size. It is
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matched by a corresponding decrease in price per bit. None of this would have been possible if it were not for a corresponding increase in realiability. Though there were problems with integrated circuit reliability in the early days, when these teething troubles were over it was found that integrated circuits were much more reliable than the mass of components that preceded them, partly because of the use of passivated junctions, but mainly because of the elimination of large numbers of interconnects between different metals in formerly conventional assemblies. But we have now anticipated the historical development.
C. The Integrated Circuit Situation in the Mid-1960s In the United States, the integrated circuit market was dominated by military use, which had 72% of the market in 1965. The hearing aid (1963) was practically the only consumer application. The Minuteman missile had sustained the first major application. Typical companies included TI, Fairchild, G.M.E., National (1967) and Intel (1968). Some older companies, such as RCA and AT&T, who had dominated semiconductor research earlier, at this time largely ignored the integrated circuit, which was to have such a revolutionary effect on telecommunications. TI introduced standard logic circuits in 1965, a change which led on to the cell library, in which such cells were regarded as elements in the design of larger chips. Japan began IC research in 1964, and by 1965 eight large vertically integrated companies were making ICs. The U.K. was also at that time dominated by military application. Plessey concentrated on linear circuits and Ferranti on digital. Despite the smaller scale of operation, developments were world-class and did not rely on licensed technology. This is illustrated next by a number of examples, drawn from the experience of one manufacturer, Plessey. This choice reflects the author’s knowledge and should not be taken as underrating the contributions of the other indigenous companies. Plessey established the concept of customer design on a standard invariant process in 1964, began commercial sales in 1965, and converted its planar process production line to ICs in 1966, phasing out discretes a year later. A single major technical advance remains to be described. VI. THEFIELDEFFECTTRANSISTOR
The field effect transistor, FET, in which the charge on one plate of a capacitor modulates the conductance of a semiconductor channel on the other, was early demonstrated by Shockley and Pearson in germanium.
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Large-scale development awaited the use of a capacitor formed in the thermal oxide of silicon, when an applied voltage could turn on conductance in a channel beneath it (Fairchild, 1962). Many firms turned to this conceptually simple device, but problems of stability were not solved for several years. Then the problems of accidental contamination of the oxide by impuries was realized, and techniques were developed to reduce the charge trapped near the silicon/silica interface. It turned out that integrated circuits using this type of FET, the MOSFET, did not require a special isolation process, and thus were smaller and simpler than bipolar circuits. Also a variant, CMOS, which now dominates logic, requires almost no power except when the logic gate is switched. VII . THE INFORMATION TECHNOLOGY REVOLUTION The technology was now in place for the IT revolution through cheap, reliable circuit complexity by photolithography. These were t o be complemented by the development of circuit design skills, culminating in efficient right-first-time designs for complex products using CAD suites and a data base or library of previous designs. Subsequent developments in integrated circuits have been on an immense financial scale, but have been evolutionary, not revolutionary. They include the use of ion implantation to control the dose of impurity incorporated by diffusion, and the development of multilayer metal conductors. Most developments have been aimed at decreasing the feature size of chips, and hence increasing circuit complexity or decreasing cost. Lithographic tools have been transformed to attain the dimensional control required to better than a tenth of a micron, and they have been matched by the development of dry etching processes to transfer the fine pattern in resist to the silicon. VIII. U.K. PROGRESS IN ICs
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These will be illustrated by chip designs from Plessey Semiconductors or its research arm at Caswell, Towcester. Recently, Plessey Semiconductors took over Ferranti’s IC operation, and then in turn Plessey was taken over by G.E.C.-Siemens and later allocated to G.E.C. This ultimately brought almost all the remaining manufacture by indigenous companies under one management in G.E.C. Plessey Semiconductors.
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A . The Expanding Opportunity for Integrated Circuits
The scope for integrated circuits is now well known, but at any one time it has been difficult to see how large the next steps will be and how radical the effect on industry as a whole. Application to logic was historically the first and led on to widespread application to computers in science and engineering, banking, and finance. The obvious application to radio began in 1966, and TV followed. More radical was the use in memory, previously dominated by nonvolatile magnetic memory. But semiconductors could show lower costs, and with the development of the 1K DRAM of 1968, the way was open for the virtual extinction of core memory and the use of vastly increased memory at lower costs. Memory now is the largest IC product, and though a fiercely competitive market leads the technology. The microprocessor followed in 1971 and progressed through more complex processors until the operations of a complete work station can now be obtained on a single chip. To expand further, the industry then needed to satisfy, or often to create, demands for chips from individual consumers rather than in professional markets. Calculators and electronic controls for “white goods” were followed by games computers, word processors, and personal computers and by great changes in “home entertainment electronics.’’ Automobile electronics can account for as many as 15 microprocessors in a luxury car. Personal communications networks will increase the already large dependence on chips of telephones, answering machines, and fax, apart from the total dependence of the telecommunications network itself on highly specialized products. In the future we are promised chips for bandwidth compression in the videophone and HDTV, machine translation and speech recognition, while the availability of cheaper nonvolatile semiconductor memory will be a new feature in the memory market. Past experience suggests that new applications, not now widely envisaged, will emerge to fuel more growth. B. What Went Wrong?
Despite an excellent position in early R & D, and some notable products and processes, the indigenous U.K. effort is unimportant in world production, and there is little sign of the dynamic of new product opportunities creating fresh businesses in electronics and information technology. There have, of course, been many analyses of the decline of the world market share not just of Britain and Europe, but of the West as a whole. We will rehearse some of the arguments.
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FIGURE1. 1962. Early planar designs for a digital integrator.
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FIGURE 2. The first successful analog feedback IC amplifier (-5 MHz). The circuit and its conventional discrete realization are shown, together with a 1-in. wafer with a number of potential ICs. 6- and 8-in. diameter wafers are now most commonly used.
FIGURE 3. A chip photograph of the amplifier. Note that the feature size is 25pm, in contrast to features between 0.5 and 2 p m today. Many lithographic defects apparent on the chip reflect the primitive contact lithography and cleam-room practice of the time.
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FIGURE4. 1963. A later version of the same amplifier, incorporating improved interdigitated transistors.
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FIGURE 5 . A logarithmic amplifier with 165 MHz bandwidth. High-frequency radio amplifiers were a strong feature of Plessey’s business in the 1960s and subsequently, and were frequently in advance of U.S.designs.
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FIGURE 6. 1966. An rf/if amplifier with 20 dB gain and 150 MHz bandwidth. Note the large area occupied by capacitors (in black). Such designs were intended for military or avionic use.
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FIGURE 7. 1967. A divide-by-two circuit, operating at 200 MHz, a high speed at the time, first used in frequency synthesis in military radio. Unlike their discrete counterparts, such circuits were built very largely from active components, which occupied a smaller area than passive components.
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FIGURE8. 1967. A variable decade divider used in frequency synthesis.
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FIGURE 9. 1969. A variable two-decade divider using MOS circuitry at 2 MHz. Note how complexity has increased, both as a result of the simpler MOS circuits, and with improving technology. Two layers of metal allow cross-overs to be effected without penalty.
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FIGURE10. 1970. A self-scanned photodiode array was used for high-speed optical character recognition in banks. The array consists of 72 x 5 photodiodes with amplifiers and row and column addressing circuits.
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FIGURE1 1 . 1972. The world’s first 1 GHz divider.
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FIGURE12. 1982. A I ,024-element video delay line using charge-coupled device technology. The serpentine configuration avoids discontinuities in charge collection. CCDs are more familiar as the active optical element in video cameras, but can also be used as here in signal processing.
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FIGURE 13. 1987. A 1 GHz divide-by-four circuit, originally produced as a demonstrator for the 1 pm bipolar process in the U.K. Alvey program. Over the period of 20 years since the earlier example shown in Fig. 7, the operating frequency of state-of-the-art circuits for this application had increased 2O-fold, largely as a result of decreases in feature size, with an accompanying shrinkage in the vertical dimension.
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FIGURE 14. 1989. A 406,000 transistor asynchronous time multiplex switch, for use in packet switching in telecommunications. The switch uses 1 pm CMOS technology also developed as part of the Alvey program, and three layers of metal interconnect. Metal interconnect now dominates the surface of the chip, and the development of fine features in the metal and dielectric layers rivals in difficulty the delineation of fine features in the silicon itself.
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FIGURE15. 1990. A I . 3 GHz all-parallel 5-bit analog-to-digital converter. Although most of today’s complex chips are largely or completely digital, analog connections are usually necessary to communicate with the outside world.
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FIGURE16. 1992. An array of 70,000 gates, using the unstructures sea-of-gates approach. This illustrates the modern tendency to use so-called semi-custom logic for even very complex logical tasks. The metallization connecting the gates can be designed by the end customer using a basic chip used by many customers. This cuts costs and shortens the design cycle. (Photo, GEC Plessey Semiconductors.)
C. Characteristics of the Industry The industry suffers from very high R & D costs, as new process variants, often involving smaller feature sizes, make earlier processes obsolescent. Items of production equipment for lithography, dry etching, and ion implantation may cost a million pounds or so, and are now essential for research, too. A minimal sustainable investment will be of the order of ten million pounds per year. These costs are small compared with the capital costs of production, where wafer “fabs” will cost something like a hundred
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FIGURE 17. 1992. A microcomputer, combining all the elements of a work station on a single die. The chip is only 8.37 x 7.58mm and embodies 98,019 0.8pm CMOS transistors. It contains a 32-bit RISC processor, a memory controller, an I/O controller, a bus interface, and a videolaudio controller. (Photo, GEC Plessey Semiconductors.)
million pounds, and plant for the largest volume product, memory, is so demanding that even the largest companies may combine to share the costs of the order of five hundred million pounds. If the plant is not to produce only low-margin products, the plant will require a large team of circuit design engineers employing expensive C.A.D. tools. Firms making such a large investment only succeed when it is coupled with engineering and marketing vision of the highest order; low-profit or loss-making activities are common. One reason for this is rapid technical obsolescence of
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processes coupled with price erosion. Time t o market is often vital to recover the original investment, It may seem surprising that under these circumstances firms stay in the race, and indeed many have not or have trimmed their investment. Some major firms such as Intel base their strategy entirely on selling devices on the open market. Some large firms feel that some in-house IC production is essential to underpin their much larger equipment or service businesses. New developments in ICs will obsolete older equipment or give opportunities for entirely new products, particularly in information technology, which has been entirely dependent on the growth of an underpinning chip capability, which may not be securely available in time to those firms without it. Others fear that the periodic shortages of capacity in the industry for standard products, particularly for memory, will limit their sales for equipment. A few firms have manufactured ICs entirely for their own use, but most now feel that their internal market does not offer economies of scale and offer products on the open market as well. Such firms are therefore faced with ambivalent attitudes to their investment. Fears of loss of competitiveness are not just felt by individual firms, but by national and economic groupings as well. The reaction t o this difficult situation has varied greatly in different countries.
D. Some National Attitudes Compared The U.S.A. was the largest market for ICs (now $18B in 1992), and was for a time the largest supplier. Japan became the largest supplier in 1985 because of her dominant position in the memory market, but with an increasing penetration of other overseas markets. Japan has, of course, a large internal market for ICs often for consumer products which will ultimately be exported. Its market is now the largest at $19.1B. The market for Europe is $16.5B, of which Germany and the U.K. consume the majority. The U.K. has quite a large industry based on inward investment by the U.S.A., and more recently by Japan; the indigenous industry is small and focuses on specialized products, but for worldwide sale. Now it is concentrated in one supplier, GEC Plessey Semiconductors, which is said to be the largest manufacturer of ASICs (application-specific ICs) in Europe, where, unusually, it returns a satisfactory profit. The typical American supplier is a device company, sometimes with other interests, e.g., Motorola. The only major US. integrated companies who are manufacturers are AT&T and IBM. By contrast, Japanese semiconductor companies are vertically integrated with equipment companies. The growth of American device companies was much aided by the availability of venture capital at least
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until 1980. In Japan, capital has been readily available from the banks, which sometimes formed part of the company group, at low interest rates. The U.K. has had much higher interest rates, sometimes with inflation. Corporate long-term strategy is, of course, characteristic of Japan, combined with guidance and intervention from MITI, notably in their funding of work in LSI (large scale integration) from 1971, and VLSI (very large scale) from 1976 to 1979. This period transformed the competitiveness of the Japanese industry. To combat the VLSI initiative, the U.S. Department of Defense launched the Very High Performance Integrated Circuit (VHPIC) initiative, aiming particularly at increasing chip computational power, but without materially affecting economic competitiveness. Most of the U.S. industry may perhaps be characterized by medium-term opportunism, though the opportunities seized by TI, Intel, and Motorola still keep them among the world’s top 10 semiconductor companies. British initiatives have been on a smaller scale and have partly reflected the political character of the government of the day, e.g. by Labour support of Inmos. Defense-funded research has been of some importance in the past, but was superseded by first the Alvey initiative and then funding from the EC Framework program, coupled with reduced funding from the Department of Trade and Industry. Despite having processes at least in pilot plant which were little inferior to the competition, there has generally been insufficient emphasis on the range of premium products to exploit the investment to the full. The lesson seems to be that large-scale competitiveness requires simultaneous excellence in processes, products and marketing. Most of the surviving large companies are vertically integrated, deriving part of their rationale from the chip marketplace and a part from the rest of the organization. This, of course, is an uneasy situation to manage, and against modern trends in accounting, which makes each part of the organization independently responsible for its own financial performance. As success in chip manufacture seems on a national scale to be linked with growth of market share in electronics and information technology as a whole, these challenges to management and government will not go away, but must be solved by countries which wish to retain an electronics industry sharing in the growth of worldwide demand. ACKNOWLEDGMENT
The author is particularly indebted to Philip Morris’s book A History of the World Semiconductor Industry (Peter Peregrinus, 1990) for many facts outside his personal experience.
The Exploitation of Semiconductors B. L. H. WILSON Armada House, Weston, Towcesler, United Kingdom
. . . . . . . . . . . . . . Technology . . . . . . . . . . . . The Transistor . . . . . . . . . . . A. Competition between Transistor Types . . B. The Diffused Transistor . . . . . . . C. The Planar Transistor . . . . . . . . D. Discrete Transistors in the Mid-1960s . . . Integrated Circuits . . . . . . . . . . A. Planar Integrated Circuits . . . . . . B. The New Situation . . . . . . . . .
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This paper covers the discovery of the useful properties of semiconductors, and concentrates very largely on silicon integrated circuits, “chips,” whose social and economic importance far transcends the very substantial influence of other semiconductors. An accompanying paper covers gallium arsenide. It is written from the standpoint of the United Kingdom, and attempts to show how the U.K.’s substantial contribution to the early development of silicon ICs has not led to a large industry in the indigenous companies, though there is a substantial industry which manufactures chips on processes developed elsewhere, sustained by inward investment. Some reasons are suggested for this failure. The paper is written from the point of view of someone closely associated with the IC development in Plessey, which was one of the leading companies in U.K. integrated circuit development for nearly 30 years. As such, it does not explicitly recognize the substantial contributions made by many other U.K. companies, such as Phillips, S.T.C., G.E.C., Ferranti, and Inmos. 141
Copyright 0 1995 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-014733-5
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I. PREHISTORY
The first observation of semiconducting properties is sometimes said to be the observation of Faraday of the negative temperature coefficient of resistance in silver sulfide in 1835. Two years later, Rochenfeld was the first to observe rectifying contacts. Although there were many relevant observations throughout the 19th century, particularly of photoconductivity, we will now skip to the early days of radio, where point contact rectifiers on various semiconductors were found to be efficient detectors in the period 1902-1906 (Bose, Pierce); Pickard observed that silicon was among these materials. Though cat’s whiskers became familiar to many until they were largely supplanted by valves, no real scientific development occurred until the Second World War. In the meantime, a substantial semiconductor industry had sprung up to expoit the rectifying properties of copper oxide and selenium, the first selenium rectifiers being produced commercially in 1927. There were, however, a number of anticipations of the (field-effect) transistor between the wars by Lilienfeld and others in the 1920s. The first published scientific account of a device that actually worked was by Hilsch and Pohl in 1935. The geometry of their “transistor” was such that gain could only be obtained below 1 Hz. Some of the early inventors had hit on the correct principle, that charge induced on the opposite plate of a capacitor could be mobile and give current between what we should now call source and drain. They failed to appreciate how easily it could be trapped at surface or interface states. 11. THECONCEPTUAL FRAMEWORK
It is unlikely that any substantial technology could have emerged before an adequate scientific framework had been put in place. The quantum theory of metals was first developed by Sommerfeld and Bloch in 1928, and this was followed by Wilson’s paper on the quantum theory of semiconductors in 1932. It developed a theory of electron and hole conduction in terms of contributions by impurities, which had respectively one more or one less electron than the host semiconductor. Wilson, an Englishman, later published a substantial book on the theory of metals (and semiconductors), which still seems surprisingly modern. He subsequently went into metallurgy as a business and was remarkably successful. At that time, no-one in the West was thinking about what might happen if both electron conduction and hole conduction were present in different parts of the same semiconductor. The Russian physicist Davydov published his theoretical paper
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in 1938 on the properties of such p-n junctions, including minority carrier injection, but despite the fact that the paper was available in English translation, it required the stimulus of the war for practical demonstration. 111. TECHNOLOGY
The development of radar during the war provided the incentive for a new investigation of the point contact diode detector at what were then felt to be high frequencies. B.T.H. at Rugby contributed notably to the British work, but much the largest and most widely distributed effort took place in the U.S.A., notably at Bell and Purdue. This included the development of techniques for the chemical control of purity of germanium and silicon, the preparation of polycrystalline material, and developments in sawing, polishing, and etching. p-n junctions were studied by Oh1 in 1941. Remarkably, the importance of single-crystal growth was not realized, and even when Teal and Little grew the first germanium crystals in 1948, it was without the support of their laboratory head, Shockley, who led the Bell laboratories team. Subsequently, Teal left Bell for Texas Instruments, where he succeeded in growing single crystals of silicon, providing a technical boost to Texas’s capability in what was destined t o be the most important semiconductor. IV. THETRANSISTOR As is well known, the first transistor was invented by Bardeen and Brittain in 1947, though the invention was not disclosed until 1948. They were
members of a team at Bell laboratories doing fundamental work on semiconductors, in this instance the study of surface states. To probe the surface, a second point electrode was brought down close to the point of a point contact rectifier, and it was realized that under appropriate circumstances the second wire could act as a control electrode for the current injected from the first. The importance of the discovery was rapidly realized, even though the early transistors were unstable and noisy. During the period 1948-1951, Shockley developed the p-n junction transistor, which overcame many of the early problems. The invention commanded worldwide attention: The prospects of a device without the large bulk, complexity, unreliability, large power drain, and limited life of the valve were quickly realized.
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A . Competition between Transistor Types
An early type of junction transistor t o emerge was the alloy transistor (1950). A thin die or chip of semiconductor, almost always germanium, had fired into its two opposing faces small beads of metal, typically indium. As the molten metal cooled down, dissolved germanium grew in the pits which the molten metal had etched. The regrown regions were doped with indium, and the resultant structure was a p-n-p alloy transistor. Although production required complex jigs made from carbon or steel, and not many transistors were made in a batch, it was comparitively simple, and the process was copied and licensed very widely. More transistors could be made simultaneously if the transistor structure was made during growth of the original crystal, by overdoping the original doping with an impurity of opposite type added to the melt, and then overdoping again. The region with transistor structures was cut from the grown crystal as a thick disk, which was in turn cut up into a large number of long cuboids, which formed the transistor. Although many transistors were formed simultaneously, it was necessary to grow a whole crystal to form them; this grown junction process (1951) was thus extremely uneconomical in material. Furthermore, it was hard to make contact with the narrow base region, and this early type soon became obsolete. A problem with the alloy transistor was that the emitter and collector electrodes were separated by a thickness comparable with that of the original wafer. The frequency response of the transistor was limited by the time it took for minority carriers to diffuse across this distance, several tens of microns, and could not extend much above the audio range. To solve this problem, Philco introduced the electrochemical transistor, in which an individual transistor die was mounted on a special jig so that dimples could be electrochemically etched on both sides, leaving in the transistor region only a thin web of germanium whose thickness could be monitored by its transparency. By reversing the polarity, metals could be plated onto both sides, and these could be fired in to form an alloyed transistor. Frequency responses in the megahertz region were now available. Again the process was widely licensed, though its successful deployment was to be short. Another competing type was successfully developed by Philips from the alloy transistor geometry. The doping type of the alloy dots was now of the same type as the germanium wafer, but the collector metal dot contained a second impurity of opposite type. This impurity was selected because it diffused rapidly from the alloy, producing a thin diffused base region, whose thickness was controlled by time and temperature rather than by jigging.
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Although these processes produced a substantial industry and made possible portable radios much superior to the valve radio, they suffered from a number of disadvantages. The production required complex jigs which produced only a limited number of transistors; the electrochemical process required a jig for each transistor. Lead attachment and heat sinking were often problems. The transistors were only suitable for use at ordinary temperatures and could scarcely operate above about 75 "C. Later, silicon variants on these types were introduced, which encouraged military use. Further, the exposed semiconductor surface was extremely sensitive to ambient gases, particularly water vapor. Transistors could not be vacuumencapsulated, but were mounted in sealed cans. Some secrecy surrounded formulations for statisfactory surface treatments, but even the best devices had a limited operating life of some tens of thousands of hours.
B. The Diffused Transistor Some of these disadvantages were overcome in the early diffused transistor in silicon (1956). A whole wafer was subject to two diffusion processes. The first, boron, diffusion produced a thin p-type skin over the whole of the wafer, while the second, phosphorus, diffusion covered it with an even thinner n-type skin to give an n-p-n sandwich. The geometry of the transistor was defined by a photographic process. Originally, wax was used as a mask, but this was soon abandoned. Metal was evaporated onto the whole wafer, which was then covered with photoresist. The photoresist was exposed through a photographic mask and developed so that the wafer was covered by exposed circular islands of resist. The wafer was then etched through the diffused regions of the silicon to produce structures reminiscent of the mesas of Arizona, after which the type was named. A similar step, but with a new mask and lighter etch, exposed the p-type layer for contacting, over part of the original mesa. This process, of which there were a number of variants, had several advantages. A large number of identical high-frequency structures were produced simultaneously, and much of the complex jigging was replaced by a photographic process. This was to prove of decisive importance in reducing costs, particularly when a new variant was invented which eventually solved the stability problem.
C. The Planar Transistor The planar process, which in its developed form is attributed to Hoerni at Fairchild between 1959 and 1961, made use of a process step called oxide masking. Before diffusion, the silicon wafer is thermally oxidized so that it
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is covered with an adherent layer of silica. Resist is then spun over the wafer, and exposed through a photographic mask. The resist is developed to reveal a pattern of holes in the resist, and the wafer is then dipped in hydrofluoric acid to locally dissolve the silica. After removing the resist, the wafer is placed in an oxidizing furnace for the boron diffusion. The silica masks the boron diffusion except where holes had been etched. The boron diffuses down into the wafer and for a similar distance sideways under the silica, so that the p-n junction so formed is protected by a layer of oxide. Oxide also grows over the diffused region in the oxidizing ambient of the diffusion furnace. The process is repeated using a second mask with smaller holes for the emitter diffusion of phosphorus, giving a localized diffused region aligned to the original transistor bases. Finally, metal stripes are evaporated, being again defined by photographic masks. The wafer is sawn into a large number of identical dice, which are subject to a mounting and lead attachment process that could be rapidly performed manually with suitable jigs and was later automated. This process produced very reliable high-frequency transistors, with a temperature range suitable for military and professional use, but in other applications had to compete with established alloy processes. As the collector region could be gold soldered on to a metal carrier, power transistors were also easily made.
D. Discrete Transistors in the Mid-1960s The mid-1960s saw many firms engaged in transistor manufacture in the U.S.A., Europe and Japan. Competition and the resultant price erosion was such that manufacture was not always profitable. In addition, there was competition between transistor types. Manufacturers which had licensed processes for transistor manufacture found that they became obsolescent, and unless this license was merely to back up their own in-house R & D, a new license must be bought as the process became obsolescent. Germanium, despite its shortcomings, was still dominant in volume. However, most large electronics firms felt that this was a technology that they could not afford to neglect, so radical was its influence becoming in key consumer markets, in defence, telecommunications, and computing. This thinking was to be transformed by the rise of the integrated circuit. V . INTEGRATED CIRCUITS
The idea of the integrated circuit was first put forward by a British defense engineer, G . W. A. Dummer, at a meeting of the American I.R.E. in 1952.
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The conception was that a number of components were to be fabricated in a solid block of material, the “solid circuit.” Some years elapsed before this vision could be interpreted. The driving force at the time was “miniaturization” for military purposes. There were two approaches. One was to build up, on a passive substrate such as glass, successive layers of deposited material: gold for interconnections, evaporated nichrome for resistors, and evaporated silicon monoxide for dielectric were commonly used. To these were added active diodes and transistors, often in chip form. This approach was initially easier. Simple metal masks or, later, screen printing were used to differentiate patterns in the various layers. The technique still survives, but did not go on to form a major industry. The more radical approach, the one that best approximated the original solid circuit vision, was to form all the components in a semiconductor chip in what was now to be called an integrated circuit. The first demonstration of the technique was by Jack Kilby of Texas Instruments, who created a multivibrator circuit entirely from silicon in 1958 (announced 1959), albeit connected by a bird’s nest of wires. Serious work in the U.K. began later that year at Plessey’s Caswell laboratories. However, the rise of the planar process was to transform the subject. A. Planar Integrated Circuits
The planar process with its photographic basis and its use of whole silicon wafers and passivated junctions was ideal for extension as the basis of integrated circuit technology. Resistors could be formed from the base diffusion, which was of quite high sheet resistance (200 ohms). By altering the mask pattern, resistors of a desired value could be defined. Although these resistors were temperature-dependent, in many circuits it was the ratio of resistance that mattered, and this was independent of the sheet resistance. The emitter diffusion was of low sheet resistance and could form one plate of a capacitor of which the thermally grown silica was the dielectric and the aluminum metallization was the other plate. The aluminum also formed the main interconnect between components, though cross-overs could be effected by using the emitter diffusion. However, all these components were unfortunately interconnected by the use of a common substrate. Some early circuit designs even attempted to overcome this limitation by cutting holes in the substate. In 1959, Lehovic invented a way to use the reverse-biased p-n junction to isolate the components. The idea was to place each component or group of components on a “land” of n-type material, but to surround that land by a wall of p-type material which was allowed to float with no applied bias.
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No net current could flow into the wall, so what little current did flow was a combination of the small leakage current from reverse bias for the majority of the junction with a compensating current from slightly forward bias of the remainder. Several ways of realizing this isolation compatible with the then-dominant bipolar transistor process were invented. One of the simplest was to use ap-type substrate on which a thin layer of n-type silicon could be grown by the newly invented process of vapor phase epitaxy. The lands for the components could then be formed by a deep diffusion of boron from the surface down t o the p-type substrate. Components could then be made on these lands in the way indicated earlier. More sophisticated versions of the process involved diffusion of the substrate prior to epitaxy: An n-type diffusion which was to appear beneath the transistor collector made the area of the collector an equipotential, while a p-type diffusion coincident with the later deep diffusion eased the demand for vertical penetration of the deep diffusion.
B. The New Situation This invention was to have revolutionary implications for electronic economics, though they were only slowly appreciated, particularly outside the integrated circuit industry. All components, transistors, diodes, resistors, and capacitors were defined by photolithography simultaneously. The cost of processing a wafer was the same irrespective of the complexity it contained. So at high yield the cost of each integrated circuit chip was proportional to its area. So smaller components, i.e., transistors and diodes, were cheaper than area-demanding resistors and capacitors, reversing the usual constraints. Circuits were fully designed before fabrication, as breadboarding was no longer desirable or even possible. A new breed of electronic engineer was required, the integrated circuit designer, who later was to be aided by sophisticated tools for layout, circuit analysis, and synthesis. Yields of integrated circuits were low at first, particularly for complex large-area chips, which suffered most from the defects often associated with dust. This led to the use of expensive clean rooms and protective clothing, filtered air, pure reagents and deionized water, which added greatly to costs. To pack more circuits into the wafer, it was desirable to shrink the size of features on the wafer; this also led to higher-frequency circuits largely because of a reduction in stray junction capacitance. Although the finer lithography required more expensive equipment, the main effect was to give cheaper, and potentially more complex, chips. The situation is often illustrated by the complexity of memory chips, which has risen exponentially from 1 kbit in 1968 to 16Mbits today (1992). Most of this 16-thousand-fold increase is associated with a decrease in feature size. It is
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matched by a corresponding decrease in price per bit. None of this would have been possible if it were not for a corresponding increase in realiability. Though there were problems with integrated circuit reliability in the early days, when these teething troubles were over it was found that integrated circuits were much more reliable than the mass of components that preceded them, partly because of the use of passivated junctions, but mainly because of the elimination of large numbers of interconnects between different metals in formerly conventional assemblies. But we have now anticipated the historical development.
C. The Integrated Circuit Situation in the Mid-1960s In the United States, the integrated circuit market was dominated by military use, which had 72% of the market in 1965. The hearing aid (1963) was practically the only consumer application. The Minuteman missile had sustained the first major application. Typical companies included TI, Fairchild, G.M.E., National (1967) and Intel (1968). Some older companies, such as RCA and AT&T, who had dominated semiconductor research earlier, at this time largely ignored the integrated circuit, which was to have such a revolutionary effect on telecommunications. TI introduced standard logic circuits in 1965, a change which led on to the cell library, in which such cells were regarded as elements in the design of larger chips. Japan began IC research in 1964, and by 1965 eight large vertically integrated companies were making ICs. The U.K. was also at that time dominated by military application. Plessey concentrated on linear circuits and Ferranti on digital. Despite the smaller scale of operation, developments were world-class and did not rely on licensed technology. This is illustrated next by a number of examples, drawn from the experience of one manufacturer, Plessey. This choice reflects the author’s knowledge and should not be taken as underrating the contributions of the other indigenous companies. Plessey established the concept of customer design on a standard invariant process in 1964, began commercial sales in 1965, and converted its planar process production line to ICs in 1966, phasing out discretes a year later. A single major technical advance remains to be described. VI. THEFIELDEFFECTTRANSISTOR
The field effect transistor, FET, in which the charge on one plate of a capacitor modulates the conductance of a semiconductor channel on the other, was early demonstrated by Shockley and Pearson in germanium.
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Large-scale development awaited the use of a capacitor formed in the thermal oxide of silicon, when an applied voltage could turn on conductance in a channel beneath it (Fairchild, 1962). Many firms turned to this conceptually simple device, but problems of stability were not solved for several years. Then the problems of accidental contamination of the oxide by impuries was realized, and techniques were developed to reduce the charge trapped near the silicon/silica interface. It turned out that integrated circuits using this type of FET, the MOSFET, did not require a special isolation process, and thus were smaller and simpler than bipolar circuits. Also a variant, CMOS, which now dominates logic, requires almost no power except when the logic gate is switched. VII . THE INFORMATION TECHNOLOGY REVOLUTION The technology was now in place for the IT revolution through cheap, reliable circuit complexity by photolithography. These were t o be complemented by the development of circuit design skills, culminating in efficient right-first-time designs for complex products using CAD suites and a data base or library of previous designs. Subsequent developments in integrated circuits have been on an immense financial scale, but have been evolutionary, not revolutionary. They include the use of ion implantation to control the dose of impurity incorporated by diffusion, and the development of multilayer metal conductors. Most developments have been aimed at decreasing the feature size of chips, and hence increasing circuit complexity or decreasing cost. Lithographic tools have been transformed to attain the dimensional control required to better than a tenth of a micron, and they have been matched by the development of dry etching processes to transfer the fine pattern in resist to the silicon. VIII. U.K. PROGRESS IN ICs
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These will be illustrated by chip designs from Plessey Semiconductors or its research arm at Caswell, Towcester. Recently, Plessey Semiconductors took over Ferranti’s IC operation, and then in turn Plessey was taken over by G.E.C.-Siemens and later allocated to G.E.C. This ultimately brought almost all the remaining manufacture by indigenous companies under one management in G.E.C. Plessey Semiconductors.
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A . The Expanding Opportunity for Integrated Circuits
The scope for integrated circuits is now well known, but at any one time it has been difficult to see how large the next steps will be and how radical the effect on industry as a whole. Application to logic was historically the first and led on to widespread application to computers in science and engineering, banking, and finance. The obvious application to radio began in 1966, and TV followed. More radical was the use in memory, previously dominated by nonvolatile magnetic memory. But semiconductors could show lower costs, and with the development of the 1K DRAM of 1968, the way was open for the virtual extinction of core memory and the use of vastly increased memory at lower costs. Memory now is the largest IC product, and though a fiercely competitive market leads the technology. The microprocessor followed in 1971 and progressed through more complex processors until the operations of a complete work station can now be obtained on a single chip. To expand further, the industry then needed to satisfy, or often to create, demands for chips from individual consumers rather than in professional markets. Calculators and electronic controls for “white goods” were followed by games computers, word processors, and personal computers and by great changes in “home entertainment electronics.’’ Automobile electronics can account for as many as 15 microprocessors in a luxury car. Personal communications networks will increase the already large dependence on chips of telephones, answering machines, and fax, apart from the total dependence of the telecommunications network itself on highly specialized products. In the future we are promised chips for bandwidth compression in the videophone and HDTV, machine translation and speech recognition, while the availability of cheaper nonvolatile semiconductor memory will be a new feature in the memory market. Past experience suggests that new applications, not now widely envisaged, will emerge to fuel more growth. B. What Went Wrong?
Despite an excellent position in early R & D, and some notable products and processes, the indigenous U.K. effort is unimportant in world production, and there is little sign of the dynamic of new product opportunities creating fresh businesses in electronics and information technology. There have, of course, been many analyses of the decline of the world market share not just of Britain and Europe, but of the West as a whole. We will rehearse some of the arguments.
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FIGURE1. 1962. Early planar designs for a digital integrator.
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FIGURE 2. The first successful analog feedback IC amplifier (-5 MHz). The circuit and its conventional discrete realization are shown, together with a 1-in. wafer with a number of potential ICs. 6- and 8-in. diameter wafers are now most commonly used.
FIGURE 3. A chip photograph of the amplifier. Note that the feature size is 25pm, in contrast to features between 0.5 and 2 p m today. Many lithographic defects apparent on the chip reflect the primitive contact lithography and cleam-room practice of the time.
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FIGURE4. 1963. A later version of the same amplifier, incorporating improved interdigitated transistors.
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FIGURE 5 . A logarithmic amplifier with 165 MHz bandwidth. High-frequency radio amplifiers were a strong feature of Plessey’s business in the 1960s and subsequently, and were frequently in advance of U.S.designs.
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FIGURE 6. 1966. An rf/if amplifier with 20 dB gain and 150 MHz bandwidth. Note the large area occupied by capacitors (in black). Such designs were intended for military or avionic use.
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FIGURE 7. 1967. A divide-by-two circuit, operating at 200 MHz, a high speed at the time, first used in frequency synthesis in military radio. Unlike their discrete counterparts, such circuits were built very largely from active components, which occupied a smaller area than passive components.
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FIGURE8. 1967. A variable decade divider used in frequency synthesis.
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FIGURE 9. 1969. A variable two-decade divider using MOS circuitry at 2 MHz. Note how complexity has increased, both as a result of the simpler MOS circuits, and with improving technology. Two layers of metal allow cross-overs to be effected without penalty.
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FIGURE10. 1970. A self-scanned photodiode array was used for high-speed optical character recognition in banks. The array consists of 72 x 5 photodiodes with amplifiers and row and column addressing circuits.
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FIGURE1 1 . 1972. The world’s first 1 GHz divider.
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FIGURE12. 1982. A I ,024-element video delay line using charge-coupled device technology. The serpentine configuration avoids discontinuities in charge collection. CCDs are more familiar as the active optical element in video cameras, but can also be used as here in signal processing.
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FIGURE 13. 1987. A 1 GHz divide-by-four circuit, originally produced as a demonstrator for the 1 pm bipolar process in the U.K. Alvey program. Over the period of 20 years since the earlier example shown in Fig. 7, the operating frequency of state-of-the-art circuits for this application had increased 2O-fold, largely as a result of decreases in feature size, with an accompanying shrinkage in the vertical dimension.
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FIGURE 14. 1989. A 406,000 transistor asynchronous time multiplex switch, for use in packet switching in telecommunications. The switch uses 1 pm CMOS technology also developed as part of the Alvey program, and three layers of metal interconnect. Metal interconnect now dominates the surface of the chip, and the development of fine features in the metal and dielectric layers rivals in difficulty the delineation of fine features in the silicon itself.
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FIGURE15. 1990. A I . 3 GHz all-parallel 5-bit analog-to-digital converter. Although most of today’s complex chips are largely or completely digital, analog connections are usually necessary to communicate with the outside world.
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FIGURE16. 1992. An array of 70,000 gates, using the unstructures sea-of-gates approach. This illustrates the modern tendency to use so-called semi-custom logic for even very complex logical tasks. The metallization connecting the gates can be designed by the end customer using a basic chip used by many customers. This cuts costs and shortens the design cycle. (Photo, GEC Plessey Semiconductors.)
C. Characteristics of the Industry The industry suffers from very high R & D costs, as new process variants, often involving smaller feature sizes, make earlier processes obsolescent. Items of production equipment for lithography, dry etching, and ion implantation may cost a million pounds or so, and are now essential for research, too. A minimal sustainable investment will be of the order of ten million pounds per year. These costs are small compared with the capital costs of production, where wafer “fabs” will cost something like a hundred
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FIGURE 17. 1992. A microcomputer, combining all the elements of a work station on a single die. The chip is only 8.37 x 7.58mm and embodies 98,019 0.8pm CMOS transistors. It contains a 32-bit RISC processor, a memory controller, an I/O controller, a bus interface, and a videolaudio controller. (Photo, GEC Plessey Semiconductors.)
million pounds, and plant for the largest volume product, memory, is so demanding that even the largest companies may combine to share the costs of the order of five hundred million pounds. If the plant is not to produce only low-margin products, the plant will require a large team of circuit design engineers employing expensive C.A.D. tools. Firms making such a large investment only succeed when it is coupled with engineering and marketing vision of the highest order; low-profit or loss-making activities are common. One reason for this is rapid technical obsolescence of
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processes coupled with price erosion. Time t o market is often vital to recover the original investment, It may seem surprising that under these circumstances firms stay in the race, and indeed many have not or have trimmed their investment. Some major firms such as Intel base their strategy entirely on selling devices on the open market. Some large firms feel that some in-house IC production is essential to underpin their much larger equipment or service businesses. New developments in ICs will obsolete older equipment or give opportunities for entirely new products, particularly in information technology, which has been entirely dependent on the growth of an underpinning chip capability, which may not be securely available in time to those firms without it. Others fear that the periodic shortages of capacity in the industry for standard products, particularly for memory, will limit their sales for equipment. A few firms have manufactured ICs entirely for their own use, but most now feel that their internal market does not offer economies of scale and offer products on the open market as well. Such firms are therefore faced with ambivalent attitudes to their investment. Fears of loss of competitiveness are not just felt by individual firms, but by national and economic groupings as well. The reaction t o this difficult situation has varied greatly in different countries.
D. Some National Attitudes Compared The U.S.A. was the largest market for ICs (now $18B in 1992), and was for a time the largest supplier. Japan became the largest supplier in 1985 because of her dominant position in the memory market, but with an increasing penetration of other overseas markets. Japan has, of course, a large internal market for ICs often for consumer products which will ultimately be exported. Its market is now the largest at $19.1B. The market for Europe is $16.5B, of which Germany and the U.K. consume the majority. The U.K. has quite a large industry based on inward investment by the U.S.A., and more recently by Japan; the indigenous industry is small and focuses on specialized products, but for worldwide sale. Now it is concentrated in one supplier, GEC Plessey Semiconductors, which is said to be the largest manufacturer of ASICs (application-specific ICs) in Europe, where, unusually, it returns a satisfactory profit. The typical American supplier is a device company, sometimes with other interests, e.g., Motorola. The only major US. integrated companies who are manufacturers are AT&T and IBM. By contrast, Japanese semiconductor companies are vertically integrated with equipment companies. The growth of American device companies was much aided by the availability of venture capital at least
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until 1980. In Japan, capital has been readily available from the banks, which sometimes formed part of the company group, at low interest rates. The U.K. has had much higher interest rates, sometimes with inflation. Corporate long-term strategy is, of course, characteristic of Japan, combined with guidance and intervention from MITI, notably in their funding of work in LSI (large scale integration) from 1971, and VLSI (very large scale) from 1976 to 1979. This period transformed the competitiveness of the Japanese industry. To combat the VLSI initiative, the U.S. Department of Defense launched the Very High Performance Integrated Circuit (VHPIC) initiative, aiming particularly at increasing chip computational power, but without materially affecting economic competitiveness. Most of the U.S. industry may perhaps be characterized by medium-term opportunism, though the opportunities seized by TI, Intel, and Motorola still keep them among the world’s top 10 semiconductor companies. British initiatives have been on a smaller scale and have partly reflected the political character of the government of the day, e.g. by Labour support of Inmos. Defense-funded research has been of some importance in the past, but was superseded by first the Alvey initiative and then funding from the EC Framework program, coupled with reduced funding from the Department of Trade and Industry. Despite having processes at least in pilot plant which were little inferior to the competition, there has generally been insufficient emphasis on the range of premium products to exploit the investment to the full. The lesson seems to be that large-scale competitiveness requires simultaneous excellence in processes, products and marketing. Most of the surviving large companies are vertically integrated, deriving part of their rationale from the chip marketplace and a part from the rest of the organization. This, of course, is an uneasy situation to manage, and against modern trends in accounting, which makes each part of the organization independently responsible for its own financial performance. As success in chip manufacture seems on a national scale to be linked with growth of market share in electronics and information technology as a whole, these challenges to management and government will not go away, but must be solved by countries which wish to retain an electronics industry sharing in the growth of worldwide demand. ACKNOWLEDGMENT
The author is particularly indebted to Philip Morris’s book A History of the World Semiconductor Industry (Peter Peregrinus, 1990) for many facts outside his personal experience.