How are semiconductors fabricated? | Explained

Like a faucet can be used to control the flow of water, semiconductors can be used to control the flow of electric currents

March 25, 2024 04:28 pm | Updated 04:31 pm IST

A close-up view of an old Intel i486SX chip from 1989, which had 0.9-1.2 million transistors.

A close-up view of an old Intel i486SX chip from 1989, which had 0.9-1.2 million transistors. | Photo Credit: Bill Fairs/Unsplash

While the physical realm of human activity contains an array of languages, the digital realm is founded on just one fundamental binary language: the 1s and 0s, also called the bits of data. Computers represent these bits as electrical signals and this forms the foundation of modern computing, communication, social media, robotics, and artificial intelligence. The 0s and 1s constantly shape the way we interact with technology and with each other on a daily basis – and the beating heart of this binary revolution is the semiconductor device.

What are semiconductors?

Semiconductors represent a distinct class of materials that possess some of the electrical properties of both conductors and insulators. Like a faucet can be used to control the flow of water, semiconductors can be used to control the flow of electric currents, and with exquisite precision.

The most important type of a semiconductor is the transistor. At the dawn of the era of modern electronics, the first integrated circuits featured four transistors. Together, they controlled the flow of currents in such a way that the circuits could perform simple arithmetic operations. Today, we have single chips boasting billions of transistors.

Fitting so many transistors on a tiny chip no bigger than a fingernail requires extreme precision and a microscopic eye for detail. For instance, the accuracy required is equivalent to dividing a strand of human hair into a thousand segments each of specific width, and further subdividing each segment into a hundred parts. This is why fabricating semiconductors involves cutting-edge technology and science.

How are semiconductors made?

The process starts with an engineer carefully selecting a silicon wafer as the foundation on which the semiconductor will be built. A team puts silicon, sourced from sand, through a meticulous purification process to separate it from other substances, until they have an ultra-pure wafer with impurity levels as low as a few parts per billion. (This percentage is comparable to an error of merely 1 cm when measuring the earth’s diameter.)

Next is the photolithography process – a crucial step that carves the circuit pattern on the wafer. The wafer is coated with a light-sensitive material called a photoresist. Then, a mask is held in front of the wafer and light is shined on it. The mask contains small gaps in the shape of the circuit pattern. The light passes through these gaps and erodes the underlying parts of the photoresist. As a result, the photoresist on the wafer ‘acquires’ the pattern of the transistor circuits.

Following photolithography, engineers use chemical and/or physical techniques to remove the uncarved parts of the photoresist, leaving behind the circuit’s structure on the silicon substrate.

Then they dope the semiconductor – i.e. deliberately add impurities to specific parts of the semiconductor to alter its electrical properties, and deposit thin layers of materials such as metals or insulators to the wafer’s surface to form electrical connections or insulate components. Then the resulting product is packaged – individual chips are separated, encapsulated, and tested to make sure they’re functional and reliable – and finally integrated into electronic devices.

What does the fabrication landscape look like?

Each step in semiconductor fabrication demands ultra-high precision and harnesses a blend of diverse scientific principles. For example, to make the most advanced transistors, the photolithography process requires a light source emitting electromagnetic radiation at a wavelength of 13.5 nm.

To achieve this, the High NA EUV machine made by the Dutch company ASML uses a cannon to shoot a 50-micrometre blob of liquid tin at 300 km/hr through a vacuum chamber, where laser beams blast it with enough energy to form a plasma that finally emits the requisite wavelength of radiation.

The semiconductor manufacturing process is characterised by specialisation, leading to an oligopoly controlled by companies specializing in specific domains. ASML, a spin-off of Philips, is in fact the sole provider of photolithography machines for cutting-edge semiconductor technology worldwide. The American firms Synopsys and Cadence dominate the software tools the engineers use to design circuits, while the silicon wafer sector is led by Japan’s Shin Etsu.

The market for the actual task of fabrication is led by Taiwan’s TSMC, with fabrication tools provided by Applied Materials and Lam Research, both headquartered in the U.S. The majority of intellectual property rights are held by British company Arm.

India boasts a leading role in chip design centred in Bengaluru. However, most of the intellectual property rights required to execute these designs are retained either by parent companies or by Arm, relegating India to being a mere user of their products. This setup is akin to the McDonald’s business model: while India may host numerous McDonald’s outlets, the recipe and supply chain are owned by a parent company headquartered in a different country.

How do semiconductors benefit us?

Smartphones and computers showcase the pinnacle of semiconductor technology but semiconductors influence nearly every facet of our lives. Semiconductors also power ‘smart’ air-conditioners’ ability to regulate the temperature as well as space telescopes’ ability to  capture both awe-inspiring and scientifically interesting images in the depths of the universe, and many other technologies in between.

Many of the solutions to the 21st century’s most important crises – including artificial intelligence, electric vehicles, space exploration, robotics, personalised healthcare, and environmental monitoring – bank on a steady supply of advanced semiconductors, underscoring their importance for the survival of the human race and its aspirations of equitability, sustainability, and justice.

Such semiconductor technology facilities foster innovation, create high-paying jobs, nurture the potential for deep-tech start-ups, and both draw from and feed into advances in materials science, computer engineering, big data, optics, chemical engineering, and chip design, to name a few.

Owing to their role in sectors like defence and automotives, semiconductors have also emerged as a focal point of geopolitical interest, with nations vying to establish semiconductor fabrication facilities within their borders and drawing industry leaders in with a plethora of incentives. The U.S. also imposed sanctions on Chinese tech companies, including bans on the acquisition of cutting-edge ASML equipment and high-end design software, for the same reason. In response, China has intensified efforts to bolster its domestic semiconductor production capabilities to meet local demand.

India, meanwhile, has been trying to use its expertise in design to establish semiconductor manufacturing plants. One hopes this strategic push plus the potential of our youth will translate to numerous opportunities for the country to seize the international semiconductor industry.

Awanish Pandey is an assistant professor at IIT Delhi with the Optics and Photonics Centre.

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