We’re all made of star stuff, as astronomer Carl Sagan was keen on reminding us. Supernova explosions, the catastrophic self-destruction of sure varieties 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. A lot of the iron in our blood and the sulfur in our amino acids originated in stars that detonated billions of years in the past. However we now have encountered one other, fairly shocking connection between supernovas and the human world—particularly, a connection to the know-how wanted to make computer chips for the most recent smartphones and different digital gadgets.
That connection emerged a number of years in the past in a collection of conversations between myself,
Jayson Stewart, and my grandfather Rudolf Schultz. My grandfather was an avid beginner sky gazer who saved a big reflector telescope within the lobby of his residence, proper by the doorway, prepared for fast deployment. Once I was 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. Extra lately, my grandfather’s astronomical perspective additionally proved serendipitously helpful in my profession, as I defined to him throughout considered one of our remark classes at his residence within the foothills of Tucson.
A double laser zap strikes a droplet of tin in ASML’s lithography machine. The primary zap flattens the drop right into a disk; the second vaporizes it right into a ball of sizzling, 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. On the time, a few decade in the past, I used to be serving to to refine a system for fabricating chips utilizing extreme ultraviolet( EUV) gentle. Though it’s crucial to creating essentially the most superior microchips right now, EUV lithography was then a difficult know-how nonetheless in improvement. To provide EUV gentle, we might focus an intense laser pulse onto 30-micrometer-wide droplets of tin flying by a chamber stuffed with low-density hydrogen. Power from the laser remodeled the droplets into balls of plasma which are 40 instances as sizzling 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 by the encircling hydrogen. Sadly, 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 surroundings. (Interstellar materials consists principally of hydrogen.) To refine our EUV setup, we might file 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, reminiscent of a filter tuned to the attribute deep-red emission of energized hydrogen atoms, known as a Hydrogen-alpha, or H-alpha, filter. Even if a supernova has 1045 instances as a lot vitality as our tin blasts, the identical math describes the evolution of each varieties of explosions. The shut bodily analogy between tin-plasma shocks and supernova shocks has turned out to be key to determining find out how to cope with our vexing tin-debris drawback.
Seen by telescopic eyes, the evening 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 fashionable gear used to take advantage of superior semiconductor chips on the planet. He felt that many different beginner sky gazers like himself would like to examine this story. I informed him I’d write it up if he can be my coauthor—and he’s.
Sadly, my grandfather shouldn’t be right here to see our article accomplished. However he did stay to see these astrophysical parallels result in essential sensible penalties: They helped my group at ASML produce a vibrant, dependable EUV gentle supply, resulting in a
major advance in commercial chipmaking.
EUV and Moore’s Legislation
My journey into the world of EUV mini-supernovas began in 2012, once I was finishing a stint as a postdoctoral analysis scientist at
Los Alamos National Laboratory and in search of my first job outdoors of academia. A buddy obtained me within the prospects of working within the semiconductor industry, the place producers are engaged in a continuing, high-stakes competitors to construct smaller, quicker circuits. I realized that the lithography course of used to create options on laptop chips was at a disaster level, one which supplied 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 collection 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 scale of the options that may be transferred onto that silicon substrate is decided 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 subsequent era of chips. Lithography know-how, and doubtlessly the almost trillion-dollar electronics business, would stagnate except we may create a robust supply of shorter-wavelength, EUV gentle.
On the time, the obtainable EUV gentle sources had been too feeble by a few issue of 10. The duty of attaining such an enormous energy improve was so daunting that I debated with my household in regards to the knowledge of beginning a profession in EUV lithography. Loads of pundits recommended that the know-how may by no means be commercialized. Regardless of my trepidation, I used to be gained over by Daniel Brown, then ASML’s vice chairman of know-how improvement, who noticed EUV as one of the best ways to attain the subsequent huge leap in chip efficiency. (Daniel, a coauthor of this text, retired from the corporate on the finish of 2024.)
Amazingly, the Taylor-von Neumann-Sedov system 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 many years, 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 Legislation—the doubling of transistor depend 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 methods within the Nineteen Eighties used mercury lamps that radiated at wavelengths of 436 nanometers (violet gentle) and ultimately 365 nm (near-ultraviolet). To scale back the characteristic dimension 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 nearly 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. However ultimately, the scaling course of stagnated and engineers had been pressured to change 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 cut 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 sizzling. The wavelength of sunshine emitted by an incandescent supply is decided by its temperature. The floor of the solar, which has a temperature of 6,000 °C, radiates most strongly within the seen spectrum. Attending 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 by 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 light supply. Tin particles is swept away by a high-speed stream of hydrogen. ASML
At ASML, we settled on a sizzling, energetic tin plasma as one of the best ways to create an EUV “lightbulb.” Due to the actual means their electrons are organized, extremely excited tin ions radiate a lot of their gentle in a slim band proper across the business’s desired 13.5-nm wavelength.
The large query we confronted was find out how to create such a tin plasma reliably. The lithography course of in chip manufacturing requires a particular, extremely constant EUV radiation dose to show the photoresist, the light-sensitive materials used to create circuit patterns on the wafer. So the sunshine supply needed to ship correct quantities of vitality. Equally essential, it had to take action repeatedly for lengthy intervals of time, with no pricey pauses for restore or upkeep.
We designed a
Rube Goldberg–like system during which a molten droplet of tin is focused by two laser beams. The primary 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 initiatives it into the lithographic scanner, a bus-size instrument that makes use of the sunshine to mission patterns onto the silicon wafer.
The trendy chipmaking course of begins with an excessive ultraviolet (EUV) gentle supply. The EUV gentle is directed by an elaborate collection 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 main 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 authentic 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 “essentially the most technically superior instrument of any variety that’s ever been made.”
At 50,000 droplets per second, working beneath heavy use, every of our lithography machines has the potential to generate almost 1 trillion pulses per yr, totaling many liters of molten tin. By 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 business, it wasn’t sufficient to make the facility; we needed to
survive the facility.
Hydrogen in EUV and in Area
A steady flush of low-density hydrogen gas 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 pace of sound in hydrogen. When the supersonic tin hits the hydrogen fuel, it subsequently produces an outward-spreading shock wave—the one that’s carefully analogous to what occurs when a supernova explosion expands into the tenuous hydrogen that fills interstellar house.
The low-density hydrogen fuel can also be on the transfer, although, flowing by the machine at tons of of kilometers per hour. The fuel slows, cools, and flushes out the energetic tin particles because it goes. To find out how a lot hydrogen we would have liked to comb the tin away and to maintain the fuel from overheating, first we had to determine the full vitality launched by the laser-produced plasmas. And determining that quantity was not a trivial job.
My colleagues and I at ASML discovered an efficient method to measure the vitality of our tin explosions, not by learning the plasma immediately, however by observing the response of the hydrogen fuel. In hindsight the thought appears clear, however within the second, there was a number of fumbling round. Once I was taking pictures of the tin plasma, I saved observing a a lot bigger, crimson glowing orb surrounding it. It appeared probably that the plasma blast was inducing H-alpha emission from the hydrogen. However the observations left us with many unknowns: Why are the orbs that particular dimension (millimeters in diameter), how do they evolve, and, most essential, how can we research the glow to measure the vitality deposited into the fuel?
The shock wave produced by a laser-heated tin droplet in a skinny hydrogen ambiance is analogous sufficient to a supernova blast that they will each be described by the identical math. The entire sequence takes lower than a millionth of a second. ASML
I examined the crimson orbs utilizing a
Teledyne Princeton Instruments Pi-Max 4, an ultrafast, intensified CCD digicam that may carry out fast publicity instances on the order of nanoseconds. I paired it with a long-distance microscope lens, to gather the glow from these crimson orbs, and an Orion 2-inch extra-narrowband H-alpha bandpass filter that I bought from an astrophotography web site. The pictures I captured with this rig had been putting. Each plasma occasion was sending out a spherical shock entrance that expanded in a gradual means.
By likelihood, 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 vitality measurement I used to be in search of. In my hunt to know how blast waves evolve, I realized that astronomers had run into the identical measurement drawback when making an attempt to find out the preliminary vitality launch that had produced an noticed supernova remnant. And I knew that I additionally had the proper subject for the subsequent of my ongoing science talks with my grandfather.
The Taylor-von Neumann-Sedov system was developed within the Forties to calculate the yield of atomic bombs, nevertheless 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 vitality 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 investigate the harmful capability of newly developed
atomic weapons. One expression of these equations, known as the Taylor-von Neumann-Sedov formula, describes the radius of the shock as a perform of time. It gives a easy, direct relationship between the radius of the shock and the full vitality.
In 1949, British physicist
Geoffrey Taylor used his newly derived formulation of blast waves to find out and publish the (then-classified) vitality 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 system describes atomic-bomb shocks with radii of tons of of meters, supernova shocks that stretch throughout gentle years, and tin-plasma shocks simply millimeters extensive. All of them characterize the identical primary bodily scenario: a compact, freestanding physique releasing vitality in opposition to minimal resistance, increasing quickly right into a gaseous surrounding.
Early atomic explosions, reminiscent of this check on the Trinity Website on 16 July 1945, impressed scientists to develop new math to calculate the quantity of vitality launched. U.S. Department of Energy
Making use of the Taylor-von Neumann-Sedov system to the H-alpha pictures 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 principle and apply, nonetheless. In our EUV sources, we noticed that the H-alpha emission shouldn’t be all the time completely symmetric, which can point out that our laser-produced plasmas don’t fairly match the simplifying “point-source” assumption. We additionally tried various a variety of totally different parameters to study extra in regards to the blasts (a kind of experiment that’s clearly not attainable for supernovas). As an example, we mapped blast-wave trajectories as a perform of ambient strain, droplet dimension, laser vitality, and goal form.
Our outcomes helped us to refine our fashions and to find out one of the best ways to tailor the hydrogen surroundings in our machines to allow a clear, steady EUV supply for chip fabrication.
Advert 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 hundreds of years, researchers have designed laboratory experiments and measurement methods to re-create what was noticed within the sky. The trendy 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 vitality ranges in an atom and, lastly, the event of quantum mechanics. With out 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, identical to the shock waves produced by tin-plasma explosions in ASML’s gentle supply. Daniel Brown
The unfold of concepts has gone the opposite means as properly. As the principles of atomic physics and the absorption strains 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 Sort 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 crucial mass and implodes, leading to a violent self-destruction. Sort Ia supernovas explode in a extremely constant means, making them worthwhile “commonplace candles” with predictable intrinsic luminosities: Evaluating 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 check the growth of the universe, and so they have led to the startling discovery that the growth of the cosmos is accelerating.
In our EUV sources, we likewise purpose to have all of our explosions equivalent, in order that they function a “commonplace candle” for the EUV scanner. Our goals are decidedly extra earthly than cosmic in scale, however our ambitions are grand all the identical.
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