Since the 1960s, the chip industry has relied on lithography – a technique that uses light to print tiny patterns on silicon to mass produce microchips. Through the decades, advances in lithography have enabled the use of smaller and smaller wavelengths and thus fabricate smaller transistors. During the early years of chip innovation, lithography tools once used visible light, with wavelengths as small as 400 nanometers (nm), and then ultraviolet light (as small as 248 nm) and deep ultraviolet light (193 nm).

After the images of the circuits are recorded in the photoresist film, etching tools are used to transfer those circuit patterns into the silicon wafer, eventually forming hundreds of computer chips on each 12-inch wafer.

Advancing microelectronics is a strategic R&D direction for Berkeley Lab, and the CXRO’s activities over the last 25 years are a major component to that. In addition to collaborating with the semiconducting industry to extend Moore’s Law, CXRO researchers are also helping other Berkeley Lab scientists develop next-generation chips that are also more energy efficient than conventional silicon chips.

Berkeley Lab scientist unpacks and prepares a new 12-inch silicon wafer which will eventually form hundreds of computer chips after EUV lithography treatment. (Credit: Marilyn Sargent/Berkeley Lab)

Extremeultraviolet lithography machine

In 1997, Intel, IBM, AMD, and Motorola formed the EUV LLC consortium to fund work at three national labs – Berkeley Lab, Livermore Lab, and Sandia – to develop the world’s first EUV lithography scanner for the semiconductor industry. I had just completed my Ph.D. when I was recruited by CXRO to work on the project. I’m proud to say that our work helped lay the foundation for the full commercialization of EUV lithography, which finally happened in 2019.

“When you’re talking about the future of semiconductor manufacturing, we’re talking about extending Moore’s Law – and that has been our primary focus for decades,” says Patrick Naulleau, a leading expert in the complex science behind EUVL and the director of the Center for X-Ray Optics, a research facility located at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

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Researchers check the wafer after etching tools transfer circuit patterns onto the surface. (Credit: Marilyn Sargent/Berkeley Lab)

Q: How is EUV lithography used to make microchips? Naulleau:First, a photoresist is spread on top of a silicon wafer. A photoresist is a light-sensitive chemical film like we used to use in old-school film cameras.

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Chemically bonding glucose and fructose produces sucrose — the stuff that most people today would call sugar (or maybe table sugar). Its name comes from the French word for sugar, sucre. The disaccharide sucrose is dextrorotatory but a mixture of the monosaccharides glucose and fructose is levorotatory. "Invert sugar" is made by heating a solution of sucrose and water. The two halves of the disaccharide separate (hydrolyze) and the rotation caused by the fructose dominates. The polarization of the solution has been "inverted" but the sugars themselves have not had their chirality inverted. Doing this would require the inversion of the molecule in three separate places, which is an extremely tricky thing to do.

spectroscopy, polarimetry, defectoscopy, astronomy, platography, material research, laser applications, light modulation, agricultural production, electric power generation, environmental control devices, molecular biology, biotechnology

All sugars produced by living things are right-handed molecules, but they may rotate the polarization of light in either direction. Glucose is the most abundant simple sugar (monosaccharide) and is the primary source of energy for all living things. Its name comes from the Greek word for sweet, γλυκος (glykos). Because it rotates plane polarized light clockwise it is also known as dextrose. Fructose is another simple sugar. Its name comes from the Latin word for fruit, fructus. Because it rotates plane polarized light counterclockwise it is also known as levulose.

Chips consist of miniaturized components called transistors – tiny silicon switches that process and store data as ones and zeroes, the binary language of computers. The more transistors a chip has, the faster it can process data. The most sophisticated chip today is about the size of a fingernail and consists of more than 100 billion transistors.

Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams, Lawrence Berkeley National Laboratory and its scientists have been recognized with 14 Nobel Prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the Lab’s facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy’s Office of Science.

Extremeultraviolet lithography

Polarized light carries information. Magnetic fields, chemical interactions, crystal structures, quality variations, and mechanical stresses can all affect the polarization of a beam of light.

In this clean room at Berkeley Lab’s Center for X-Ray Optics, researchers use extreme ultraviolet lithography (EUVL) to advance the creation of next-generation, ultra-small computer chips. A human hair is 50–100 micrometers. Each image from the EUVL system is 200 x 30 micrometers and is extremely information-rich.

We’re one of the first DOE labs to develop the basic research for EUVL systems – so industry relies on us to develop new EUV research and development instrumentation such as advanced microfield lithography and microscopy tools.

Despite the successful commercial launch of EUV lithography in 2019, there’s still more basic science work to be done to keep the technology moving forward – and we continue to partner with Intel, Samsung, and other industry leaders in the drive to develop future EUV lithography systems capable of printing ever smaller, faster, and more energy-efficient chips.

Imagine a light wave traveling toward you, on its way to entering your eye. In what direction is the electric field vibrating? (Light is both electric and magnetic, but it is usually the electric field that we are interested in.) Up and down? Sure. Left and right? Sure, why not. Both alignments are perpendicular to the propagation of the wave.

Carvone is a member of a family of chemicals called terpenoids. Carvone has two enantiomers: a right-handed form which is found in the seed oils of caraway, dill, and anise; and a left-handed form which is found in spearmint oil. The difference in the two flavors is evidence that odor receptors have activation sites that are chiral. Your nose can smell the handedness of some molecules.

Then, a sophisticated camera called a lithography tool projects images of tiny circuits onto the photoresist-coated wafer using EUV light at a wavelength of 13.5 nanometers. The photoresist captures the ultrahigh resolution image of the computer chip circuits.

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DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

In 2001, as EUV lithography gained more traction across the industry as a whole, we kicked off a partnership with SEMATECH, which was a broad-based semiconductor industry consortium, to continue pushing EUV lithography research forward.

Q: How has CXRO helped drive innovation in chip making? The CXRO has helped industry understand the fundamental science behind EUVL, and how to push the technology forward.

The photoresist-coated wafer is loaded into the lithography tool and projected with tiny circuits using an EUV light. (Credit: Marilyn Sargent/Berkeley Lab)

Light is a transverse electromagnetic wave that can be seen by a typical human. Wherever light goes, the electric and magnetic fields are disturbed perpendicular to the direction of propagation. This propagating disturbance is what makes light a wave. The fact that the electric and magnetic fields are disturbed makes light an electromagnetic wave. The fact that it disturbs these fields at right angles to the direction of propagation makes light a transverse wave. In this section we will explore what it means to be transverse.

According to Naulleau, the tiny wavelength in EUVL is very close to X-ray light and therefore requires new instruments that far exceed the capabilities of early lithography, which employed longer and less energetic wavelengths of visible and ultraviolet light. (On the electromagnetic spectrum, a system scientists use to classify all ranges of light according to their corresponding wavelength, X-ray light ranges from 0.01 to 10 nanometers; extreme ultraviolet or EUV light ranges from 10 to 124 nanometers; and UV light from 124 to 400 nanometers, Naulleau explains.)

Right now, our latest lithography tools are able to produce features that are smaller than can be reliably recorded in the photoresist, so the most immediate challenge the industry is facing is in the understanding and development of new photoresist materials that will enable fabrication of chips at the 14-angstrom node (1.4 nanometers) and below. (1 angstrom is 10 million times smaller than a millimeter – or the approximate size of a single hydrogen atom.)

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Q: What is the CXRO doing now to push chip innovation forward? During the pandemic, we continued to partner with Intel and Samsung to push the capabilities of our next generation EUV lithography research tools and to develop new chemical analysis tools that allow us to understand the fundamental physics of how photoresists work.

Most light sources are unpolarized. The electric field is vibrating in many directions; all perpendicular to the direction of propagation. Polarized light is unique in that it vibrates mostly in one direction. Any direction is possible as long as it's perpendicular to the propagation, be it…

That’s our value add – we do the fundamental research needed to accelerate technology a decade ahead of the game because the microchip industry doesn’t have time to wait.

EUV lithography was recently commercialized in 2019, but it took decades of research to get there, much of which was made possible by the unique capabilities of the CXRO. For the past 25 years, CXRO scientists and engineers have worked side by side with microelectronics industry leaders to tackle the significant technological advances required to develop EUVL.

Optical rotation is the ability that all chiral molecules have to rotate plane polarized light. Think of a polarized light wave as a hand on an analog clock pointing to the 12. Shifting that hand a bit to the right rotates it clockwise, shifting it to the left rotates it counterclockwise. The Latin words for right and left are dexter and laevus, respectively. Chiral molecules that rotate the polarization clockwise are said to be dextrorotatory, while those that rotate it counterclockwise are said to be levorotatory.

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Organic compounds that exist in both left and right handed forms are called stereoisomers. Those that are perfect mirror images of one another are called enantiomers. They demonstrate equal amounts, but opposite directions of optical rotation. In all other respects, their physical and chemical properties are identical. Their physiological actions may differ, because enzymes and other biological receptors can readily discriminate between many enantiomeric pairs. The other isomers may be indigestible or even toxic. Some are just interesting.

Some analysts say that the end of Moore’s Law is near. But it could be decades before the modern chip runs out of room for improvement, thanks to advances in materials and instrumentation enabled by the CXRO, Naulleau says.

Q: How does the CXRO produce EUV light? For the past 25 years, CXRO’s EUVL instruments have harnessed light from Berkeley Lab’s Advanced Light Source, a synchrotron user facility that produces very bright extreme ultraviolet and soft X-ray light that’s guided down highly specialized instruments called “beamlines” to experiment stations.

A typical hand consists of four fingers, a thumb, and a palm. (In this context, a thumb is not considered a finger.) Using the two hands of one person, it is only ever possible to get two of these parts to point in the same direction at the same time.

Today, the chip industry has entered a new era: extreme ultraviolet lithography (EUVL), a revolutionary technique that deploys short wavelengths of just 13.5 nanometers, which is about 40 times smaller than visible light and 20 times smaller than UV light. Such a short EUV wavelength allows the microelectronics industry to print microchip circuits and transistors that are tens of thousands of times thinner than a strand of human hair – and buy more time for Moore’s Law, which predicted in 1965 that the number of transistors placed on a chip would double every two years until the technology reached its limitations in miniaturization and performance.

Chirality is the property of some objects that makes them distinguishable from their mirror images. Objects that exhibit chirality are said to be chiral. Human hands are the most easily accessible examples of chiral objects, which is why chirality is also often described as handedness. Chirality is just a painfully clever scientific word derived from the Greek word for hand — χερι (kheri).

Determining whether a particular compound is right- or left-handed is determined by a particularly complicated set of rules that I don't understand (and don't care to understand at this moment), but being able to do so is especially important in organic chemistry. Something possibly useful to know for physics students is that all naturally occurring sugars are right-handed and all naturally occurring amino acids are left-handed (except glycine, which is not chiral).

Advances in microelectronics – also known as microchips or chips – have enabled fast, powerful, compact smartphones and laptops – electronic devices that were once, long ago, the stuff of science fiction.