How Tiny Star Explosions Drive Moore’s Law

We are all made of star stuff, as astronomer Carl Sagan was keen on reminding us. Supernova explosions, the catastrophic self-destruction of sure kinds of worn-out stars, are intimately tied to life on Earth as a result of they’re the birthplaces of heavy parts throughout the universe. Most of the iron in our blood and the sulfur in our amino acids originated in stars that detonated billions of years in the past. But we have now encountered one other, fairly shocking connection between supernovas and the human world—particularly, a connection to the expertise wanted to make pc chips for the newest smartphones and different digital gadgets.

That connection emerged a number of years in the past in a sequence of conversations between myself,
Jayson Stewart, and my grandfather Rudolf Schultz. My grandfather was an avid novice sky gazer who saved a big reflector telescope within the lobby of his house, proper by the doorway, prepared for speedy deployment. When I used to be in highschool, he handed me a duplicate of Stephen Hawking’s A Brief History of Time (Bantam Books, 1988) and guided me towards a lifelong love of physics. More lately, my grandfather’s astronomical perspective additionally proved serendipitously helpful in my profession, as I defined to him throughout one in all our commentary classes at his house within the foothills of Tucson.

A double laser zap strikes a droplet of tin in ASML’s lithography machine. The first zap flattens the drop right into a disk; the second vaporizes it right into a ball of scorching, ultraviolet-emitting plasma. ASML

I used to be updating my grandfather in regards to the work I used to be doing in my lab at
ASML, a Netherlands-based firm that develops and builds gear for manufacturing semiconductor chips. At the time, a few decade in the past, I used to be serving to to refine a system for fabricating chips utilizing excessive ultraviolet( EUV) gentle. Although it’s important to creating essentially the most superior microchips at the moment, EUV lithography was then a difficult expertise nonetheless in growth. To produce EUV gentle, we’d focus an intense laser pulse onto 30-micrometer-wide droplets of tin flying via a chamber full of low-density hydrogen. Energy from the laser remodeled the droplets into balls of plasma which are 40 instances as scorching because the floor of the solar, inflicting the tin to emit intense ultraviolet radiation. As a by-product, the plasma balls generated shock waves that traveled via the encircling hydrogen. Unfortunately, the explosions additionally launched sprays of tin particles, which had been proving extraordinarily tough to handle.

Recalling my astronomy classes with my grandfather, I noticed that many points of this course of have intriguing similarities to what occurs throughout a supernova: a sudden explosion, an increasing cloud of plasma particles, and a shock wave that slams into a skinny hydrogen atmosphere. (Interstellar materials consists largely of hydrogen.) To refine our EUV setup, we’d document the evolution of the shock wave from our plasma balls, a lot as astronomers research the stays of supernovas to infer the properties of the stellar explosion that created them. We even used a number of the identical gear, similar to a filter tuned to the attribute deep-red emission of energized hydrogen atoms, referred to as a Hydrogen-alpha, or H-alpha, filter. Despite the truth that a supernova has 1045 instances as a lot power as our tin blasts, the identical math describes the evolution of each kinds of explosions. The shut bodily analogy between tin-plasma shocks and supernova shocks has turned out to be key to determining learn how to take care of our vexing tin-debris downside.

Seen via telescopic eyes, the night time sky is dotted with the glowing stays of exploded stars. My grandfather was tickled by the connection between these historic, distant celestial objects and the trendy gear used to take advantage of superior semiconductor chips on the earth. He felt that many different novice sky gazers like himself would like to examine this story. I instructed him I’d write it up if he can be my coauthor—and he’s.

Sadly, my grandfather just isn’t right here to see our article accomplished. But he did dwell to see these astrophysical parallels result in necessary sensible penalties: They helped my group at ASML produce a vivid, dependable EUV gentle supply, resulting in a
main advance in business chipmaking.

EUV and Moore’s Law

My journey into the world of EUV mini-supernovas began in 2012, after I was finishing a stint as a postdoctoral analysis scientist at
Los Alamos National Laboratory and searching for my first job outdoors of academia. A good friend bought me within the prospects of working within the semiconductor trade, the place producers are engaged in a relentless, high-stakes competitors to construct smaller, quicker circuits. I discovered that the lithography course of used to create options on pc chips was at a disaster level, one which provided intriguing engineering challenges.

In lithography, gentle is used to imprint an intricate sample onto a ready silicon substrate. This course of is repeated many instances in a sequence of etching, doping, and deposition steps to create as much as 100 layers; the patterns in these layers find yourself defining the circuitry of a pc chip. The measurement of the options that may be transferred onto that silicon substrate is set by the imaging system and by the wavelength of sunshine. The shorter the wavelength and extra energetic the sunshine, the smaller the options. The ultraviolet wavelengths in use on the time had been too lengthy and crude for the following era of chips. Lithography expertise, and probably the almost trillion-dollar electronics trade, would stagnate except we may create a robust supply of shorter-wavelength, EUV gentle.

At the time, the accessible EUV gentle sources had been too feeble by a few issue of 10. The job of reaching such an enormous energy enhance was so daunting that I debated with my household in regards to the knowledge of beginning a profession in EUV lithography. Plenty of pundits recommended that the expertise may by no means be commercialized. Despite my trepidation, I used to be gained over by Daniel Brown, then ASML’s vice chairman of expertise growth, who noticed EUV as one of the simplest ways to realize the following large bounce in chip efficiency. (Daniel, a coauthor of this text, retired from the corporate on the finish of 2024.)

Amazingly, the Taylor-von Neumann-Sedov formulation describes atomic–bomb shocks with radii of tons of of meters, supernova shocks that stretch throughout gentle years, and tin-plasma shocks simply millimeters wide.

For a long time, producers had managed to squeeze increasingly transistors onto an built-in circuit, going from about 2,000 transistors in 1971 to 200 billion in 2024. Engineers saved Moore’s Law—the doubling of transistor rely each couple of years—alive for greater than 5 a long time by incrementally decreasing the wavelength of sunshine and increasing the numerical aperture of the imaging system utilized in lithography.

Lithography techniques within the Eighties used mercury lamps that radiated at wavelengths of 436 nanometers (violet gentle) and ultimately 365 nm (near-ultraviolet). To scale back the function measurement of transistors additional, individuals invented high-power lasers that would produce ultraviolet beams at shorter, 248-nm and 193-nm wavelengths. Then the transfer to ever-shorter wavelengths hit a wall, as a result of virtually all recognized lens supplies take up gentle with wavelengths of lower than about 150 nm.

For a short while, lithographers managed to maintain making progress utilizing a intelligent trick: They
put water between the lens and the silicon wafer to enhance the focusing energy of the imaging system. But ultimately, the scaling course of stagnated and engineers had been pressured to modify to shorter wavelengths. That change, in flip, required changing lenses with mirrors, which got here with a penalty. Mirrors couldn’t obtain the identical focusing precision because the earlier lens-plus-water mixture. To make significant progress, we would have liked to drastically scale back the wavelength of the sunshine to round 13.5 nm, or about one-thirtieth the wavelength of the shortest seen violet gentle that your eye can see.

To get there, we’d want one thing insanely scorching. The wavelength of sunshine emitted by an incandescent supply is set by its temperature. The floor of the solar, which has a temperature of 6,000 °C, radiates most strongly within the seen spectrum. Getting to EUV gentle with a wavelength of 13.5 nm requires a supply with an especially excessive temperature, round 200,000 °C.

Tin droplets fall via ASML’s lithography machine. Laser beams strike the passing droplets 50,000 instances a second, inflicting them to glow and making a steady excessive ultraviolet gentle supply. Tin particles is swept away by a high-speed movement of hydrogen. ASML

At ASML, we settled on a scorching, energetic tin plasma as one of the simplest ways to create an EUV “lightbulb.” Because of the actual method their electrons are organized, extremely excited tin ions radiate a lot of their gentle in a slender band proper across the trade’s desired 13.5-nm wavelength.

The large query we confronted was learn how to create such a tin plasma reliably. The lithography course of in chip manufacturing requires a particular, extremely constant EUV radiation dose to reveal the photoresist, the light-sensitive materials used to create circuit patterns on the wafer. So the sunshine supply needed to ship correct quantities of power. Equally necessary, it had to take action constantly for lengthy durations of time, with no expensive pauses for restore or upkeep.

We designed a
Rube Goldberg–like system through which a molten droplet of tin is focused by two laser beams. The first turns the droplet right into a pancake-shaped disk. The second laser hits the tin with a brief, energetic laser pulse that converts it right into a high-temperature plasma. An almost hemispherical, multilayer mirror then collects EUV gentle from the plasma and tasks it into the lithographic scanner, a bus-size instrument that makes use of the sunshine to venture patterns onto the silicon wafer.

The fashionable chipmaking course of begins with an excessive ultraviolet (EUV) gentle supply. The EUV gentle is directed by an elaborate sequence of mirrors onto the floor of a transferring wafer, the place it creates the specified sample of imprinted circuits. ASML

Sustaining an EUV gentle supply intense sufficient for lithography requires a major laser with an influence of a number of tens of kilowatts, zapping about 50,000 droplets of tin each second. In lower than one ten-millionth of a second, every laser pulse transforms the tin from a 30-micrometer-wide droplet right into a millimeter-wide plasma explosion with tens of 1000’s of instances its unique quantity.
Mark Phillips, the director of lithography and {hardware} options at Intel, described the EUV lithography machine we had been serving to to develop as “the most technically advanced tool of any kind that’s ever been made.”

At 50,000 droplets per second, working below heavy use, every of our lithography machines has the potential to generate almost 1 trillion pulses per 12 months, totaling many liters of molten tin. Through all of that, a single nanometer of tin particles coating the collector optic would degrade the EUV transmission to unacceptable ranges and put the machine out of fee. As we are saying within the trade, it wasn’t sufficient to make the facility; we needed to
survive the facility.

Hydrogen in EUV and in Space

A steady flush of low-density hydrogen fuel protects the mirror and surrounding vessel from the spray of vaporized tin ejecta. That particles has an preliminary velocity of tens of kilometers per second, a lot quicker than the velocity of sound in hydrogen. When the supersonic tin hits the hydrogen fuel, it due to this fact produces an outward-spreading shock wave—the one that’s intently analogous to what occurs when a supernova explosion expands into the tenuous hydrogen that fills interstellar area.

The low-density hydrogen fuel can also be on the transfer, although, flowing via the machine at tons of of kilometers per hour. The fuel slows, cools, and flushes out the energetic tin particles because it goes. To decide how a lot hydrogen we would have liked to brush the tin away and to maintain the fuel from overheating, first we had to determine the full power launched by the laser-produced plasmas. And determining that quantity was not a trivial job.

My colleagues and I at ASML discovered an efficient option to measure the power of our tin explosions, not by learning the plasma instantly, however by observing the response of the hydrogen fuel. In hindsight the concept appears clear, however within the second, there was a variety of fumbling round. When I used to be taking photos of the tin plasma, I saved observing a a lot bigger, pink glowing orb surrounding it. It appeared doubtless that the plasma blast was inducing H-alpha emission from the hydrogen. But the observations left us with many unknowns: Why are the orbs that particular measurement (millimeters in diameter), how do they evolve, and, most necessary, how can we research the glow to measure the power deposited into the fuel?

The shock wave produced by a laser-heated tin droplet in a skinny hydrogen environment is analogous sufficient to a supernova blast that they’ll each be described by the identical math. The complete sequence takes lower than a millionth of a second. ASML

I examined the pink orbs utilizing a
Teledyne Princeton Instruments Pi-Max 4, an ultrafast, intensified CCD digicam that may carry out speedy publicity instances on the order of nanoseconds. I paired it with a long-distance microscope lens, to gather the glow from these pink orbs, and an Orion 2-inch extra-narrowband H-alpha bandpass filter that I bought from an astrophotography web site. The photos I captured with this rig had been putting. Every plasma occasion was sending out a spherical shock entrance that expanded in a gradual method.

By probability, months earlier, I had attended a seminar that talked about blast waves—shock waves produced by a point-source explosion. That seminar satisfied me that our observations may give me the power measurement I used to be searching for. In my hunt to know how blast waves evolve, I discovered that astronomers had run into the identical measurement downside when making an attempt to find out the preliminary power launch that had produced an noticed supernova remnant. And I knew that I additionally had the proper subject for the following of my ongoing science talks with my grandfather.

The Taylor-von Neumann-Sedov formulation was developed within the Forties to calculate the yield of atomic bombs, however it additionally describes the evolution of plasma shock waves in our EUV lithography system and in distant supernovas. It relates the shock wave’s radius (R) over time to the power launched (E), fuel density (ρ), and a gas-dependent parameter (C).

To get a solution, astronomers turned to equations that had been found within the Forties, when scientists had been looking for methods to research the damaging capability of newly developed
atomic weapons. One expression of these equations, referred to as the Taylor-von Neumann-Sedov formulation, describes the radius of the shock as a operate of time. It gives a easy, direct relationship between the radius of the shock and the full power.

In 1949, British physicist
Geoffrey Taylor used his newly derived formulation of blast waves to find out and publish the (then-classified) power yield of the primary atomic-bomb detonations. Taylor’s success, which reportedly upset the United States authorities, demonstrated the facility of his evaluation. Amazingly, the Taylor-von Neumann-Sedov formulation describes atomic-bomb shocks with radii of tons of of meters, supernova shocks that stretch throughout gentle years, and tin-plasma shocks simply millimeters broad. They all signify the identical fundamental bodily scenario: a compact, freestanding physique releasing power towards minimal resistance, increasing quickly right into a gaseous surrounding.

Early atomic explosions, similar to this take a look at on the Trinity Site on 16 July 1945, impressed scientists to develop new math to calculate the quantity of power launched. U.S. Department of Energy

Applying the Taylor-von Neumann-Sedov formulation to the H-alpha photos we recorded within the ASML gentle supply resulted in a satisfying settlement between our calculated energies and the quantities we had roughly estimated by different means. We additionally encountered some discrepancies between idea and follow, nevertheless. In our EUV sources, we noticed that the H-alpha emission just isn’t at all times completely symmetric, which can point out that our laser-produced plasmas don’t fairly match the simplifying “point-source” assumption. We additionally tried various plenty of completely different parameters to study extra in regards to the blasts (a kind of experiment that’s clearly not attainable for supernovas). For occasion, we mapped blast-wave trajectories as a operate of ambient strain, droplet measurement, laser power, and goal form.

Our outcomes helped us to refine our fashions and to find out one of the simplest ways to tailor the hydrogen atmosphere in our machines to allow a clear, secure EUV supply for chip fabrication.

Ad Astra per Aspera

The connection between supernovas and laser-produced plasmas is only one instance of an extended historical past of advances in physics and engineering that had been impressed by astronomy. For centuries, researchers have designed laboratory experiments and measurement methods to re-create what was noticed within the sky. The fashionable description of the atom can hint its roots to the invention of the prism and the spreading of the photo voltaic spectrum into its composite colours, which led to the identification of discrete power ranges in an atom and, lastly, the event of quantum mechanics. Without quantum mechanics, many fashionable electronics applied sciences wouldn’t be attainable.

Barnard’s Loop [left], within the constellation Orion, is the remnant of an historic supernova. It glows in Hydrogen-alpha gentle, similar to the shock waves produced by tin-plasma explosions in ASML’s gentle supply. Daniel Brown

The unfold of concepts has gone the opposite method as effectively. As the principles of atomic physics and the absorption traces of gases had been characterised in lab experiments, astronomers used spectroscopic observations to find out the composition of the solar, to infer the life cycles of stars, and to measure the dynamics of galaxies.

I discover it fascinating that the laser-produced plasmas we use in our EUV gentle supply particularly resemble one specific number of supernova, generally known as Type Ia. This sort of supernova is assumed to happen when a white dwarf star pulls materials from a neighboring companion star till it reaches a important mass and implodes, leading to a violent self-destruction. Type Ia supernovas explode in a extremely constant method, making them useful “standard candles” with predictable intrinsic luminosities: Comparing their obvious brightness to their true, intrinsic luminosity makes it attainable to measure their distances from us precisely throughout billions of sunshine years. These supernovas are getting used to review the enlargement of the universe, they usually have led to the startling discovery that the enlargement of the cosmos is accelerating.

In our EUV sources, we likewise intention to have all of our explosions similar, in order that they function a “standard candle” for the EUV scanner. Our goals are decidedly extra earthly than cosmic in scale, however our ambitions are grand all the identical.