VOL 38, NO 8, 1965

“The complexity [of integrated circuits] for minimum costs has increased at a rate of roughly a factor of two per year/’ – Gordon E Moore, Electronics,

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This year marks the 50 years of the reign of ‘Moore’s Law’ in electronics. Gordon Moore, the co-founder of Intel, made a pre­diction in 1965 that the number of transistors on a chip and the raw computing power of microchips would double every year, while the cost of production would remain the same. The only correction to Moore’s Law 50 years later is that the dou­bling is occurring every 18 months, instead of a year.

When Moore made this predic­tion, chips had only 50 transistors; today, a chip can have more than 4 billion transistors. Thus, the power of the chip has increased by a factor of 80 million in about 50 years!

As for cost, when transistors were commercialised in the early 1950s, one of them used to be sold for $49.95; in 2015 you can buy a million transistors for less than a dollar. The reduced costs allow chips to be used in a wide range of modern products and not just computers and space rockets. They control cars, micro- wave ovens, washing machines, cell phones, TVs, machine tools, wrist- watches, radios, audio systems and even toys. In India already millions of credit cards, debit cards, driving licences, ID and access cards, etc, contain chips.

The global electronics industry is producing a billion transistors per year for every person on the earth’s 7 billion inhabitants! The global semi­conductor industry is estimated to be a $300 billion-a-year business. Elec­tronics, a technology that was born at the beginning of the twentieth century with the discovery of the electron, has today been integrated
into everything imaginable.

Considering the breathtaking advances in the power of chips and the equally astonishing reduction in their cost, people sometimes wonder whether this trend will continue for­ever. Or, will the growth come to an end soon and the so-called Moore’s Law cease to be valid?

Printing technology and chip- making

The chip-making process, in its essence, resembles the screen-print­ing process used in the textile indus­try. How is micro-miniature design achieved? We have all kinds of super­fine works of art, including calligra­phy of a few words on a grain of rice. But the same grain of rice should now accommodate a circuit contain­ing about 100,000 transistors!

How do chipmakers pull off something so incredible? They use
very short wavelength light (ultra­violet light) and sophisticated optics to reduce the detailed circuit dia­grams to a thousandth of their size. These films are used to create sten­cils (masks) made of materials that are opaque to light. The masks are then used to cast shadows on pho­to-sensitive coatings on the silicon wafer, using further miniaturisa­tion with the help of laser light, elec­tron beams and ultra-sophisticated optics to imprint the circuit pattern on the wafer. The process is called photolithography.

Of course, we are greatly simpli­fying the chip-making methodol­ogy for the sake of explaining the main ideas. The fineness of this pro­cess is measured by how thin a chan­nel one can etch on silicon. So, when someone tells you about 45 nano­metre (nanometre is one millionth of a millimetre) technology being used by leading chipmakers, they are referring to high-tech scalpels that can etch channels as thin as 45 nanometres. To get a sense of pro­portion, that is equivalent to etching over 2,000 parallel ridges and vales on the diameter of a single strand of human hair!

In 2010, most fabs used 45 nano­metre technology; in 2015, many leading fabs have commercialised 22 nanometre technology and are experimenting with 14 nanometre technology in their labs. What does this mean? Well, roughly each new technology is able to etch a transis­tor in half the surface area of the sili­con wafer than the previous one – lo and behold the ‘secret’ of Moore’s Law of doubling transistor density on a chip!

What are the problems in con­tinuing this process? Making the scalpels sharper is one. Sharper scal­pels mean using shorter and shorter wavelengths of light for etching. But, as the wavelength shortens we reach the X-ray band, and we do not yet have X-ray lasers or optics of good quality in that region.

There is another hurdle. As circuit designs get more complex and etch­ing gets thinner, the masks too become thinner. A law in optics says that if the dimensions of the chan­nels in a mask are of the order of the wavelength of light, then, instead of casting clear shadows, the masks will start ‘diffracting’ – bands of bright and dark regions would be created around the edges of the shadow, thereby limiting the production of sharply defined circuits.

Moreover, as the channels get thinner there are greater chances of electrons from one channel crossing over to the other due to defects, lead­ing to a large number of chips failing at the manufacturing stage. Surpris­ingly. though, ingenious engineers have overcome the hurdles and come up with solutions that have resulted in further miniaturisation.