We’re 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 components throughout the universe. Many 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 have now encountered one other, fairly shocking connection between supernovas and the human world—particularly, a connection to the expertise wanted to make computer 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 beginner sky gazer who stored a big reflector telescope within the lobby of his dwelling, proper by the doorway, prepared for fast deployment. Once I was in highschool, he handed me a replica 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 statement classes at his dwelling 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 couple of 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 vital to creating probably the most superior microchips immediately, EUV lithography was then a difficult expertise nonetheless in improvement. To provide EUV gentle, we might focus an intense laser pulse onto 30-micrometer-wide droplets of tin flying by means of a chamber full of low-density hydrogen. Power from the laser remodeled the droplets into balls of plasma which can be 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 means of the encircling hydrogen. Sadly, the explosions additionally launched sprays of tin particles, which have been proving extraordinarily troublesome to handle.
Recalling my astronomy classes with my grandfather, I noticed that many elements 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 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 similar gear, similar to a filter tuned to the attribute deep-red emission of energized hydrogen atoms, known as a Hydrogen-alpha, or H-alpha, filter. Even though a supernova has 1045 instances as a lot vitality 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 cope with our vexing tin-debris downside.
Seen by means of 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 trendy 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 instructed him I might write it up if he could 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 vivid, 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, after I was finishing a stint as a postdoctoral analysis scientist at
Los Alamos National Laboratory and searching for my first job exterior of academia. A buddy acquired me within the prospects of working within the semiconductor industry, the place producers are engaged in a relentless, 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 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 dimensions 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 have been too lengthy and crude for the subsequent era of chips. Lithography expertise, and probably the almost trillion-dollar electronics trade, would stagnate except we might create a robust supply of shorter-wavelength, EUV gentle.
On the time, the accessible EUV gentle sources have been too feeble by a couple of 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 expertise might by no means be commercialized. Regardless of my trepidation, I used to be gained over by Daniel Brown, then ASML’s vp of expertise improvement, who noticed EUV as the easiest way to realize the subsequent large soar in chip efficiency. (Daniel, a coauthor of this text, retired from the corporate on the finish of 2024.)
Amazingly, the Taylor-von Neumann-Sedov method describes atomic–bomb shocks with radii of a whole bunch 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 more transistors onto an built-in circuit, going from about 2,000 transistors in 1971 to 200 billion in 2024. Engineers stored Moore’s Legislation—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 methods 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 characteristic measurement of transistors additional, folks invented high-power lasers that might 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 identified lens supplies soak up gentle with wavelengths of lower than about 150 nm.
For a short time, 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 have 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 wanted 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 set 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 a particularly excessive temperature, round 200,000 °C.
Tin droplets fall by means of 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 the easiest way to create an EUV “lightbulb.” Due to the actual manner 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 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 vitality. Equally essential, it had to take action constantly 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. A virtually hemispherical, multilayer mirror then collects EUV gentle from the plasma and initiatives it into the lithographic scanner, a bus-size software that makes use of the sunshine to undertaking 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 sequence of mirrors onto the floor of a shifting 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 hundreds of instances its authentic quantity.
Mark Phillips, the director of lithography and {hardware} options at Intel, described the EUV lithography machine we have been serving to to develop as “probably the most technically superior software of any sort 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 yr, totaling many liters of molten tin. Via 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 ability; we needed to
survive the ability.
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 velocity of sound in hydrogen. When the supersonic tin hits the hydrogen gasoline, 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 gasoline can be on the transfer, although, flowing by means of the machine at a whole bunch of kilometers per hour. The gasoline slows, cools, and flushes out the energetic tin particles because it goes. To find out how a lot hydrogen we wanted to comb the tin away and to maintain the gasoline 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 technique to measure the vitality of our tin explosions, not by finding out the plasma straight, however by observing the response of the hydrogen gasoline. In hindsight the thought appears clear, however within the second, there was a variety of fumbling round. Once I was taking photographs of the tin plasma, I stored observing a a lot bigger, purple glowing orb surrounding it. It appeared seemingly 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 measurement (millimeters in diameter), how do they evolve, and, most essential, how can we research the glow to measure the vitality deposited into the gasoline?
The shock wave produced by a laser-heated tin droplet in a skinny hydrogen ambiance is analogous sufficient to a supernova blast that they’ll each be described by the identical math. The entire sequence takes lower than a millionth of a second. ASML
I examined the purple 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 purple 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 have been hanging. Each plasma occasion was sending out a spherical shock entrance that expanded in a gradual manner.
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 might give me the vitality measurement I used to be searching for. In my hunt to know how blast waves evolve, I realized that astronomers had run into the identical measurement downside when trying to find out the preliminary vitality launch that had produced an noticed supernova remnant. And I knew that I additionally had the proper matter for the subsequent of my ongoing science talks with my grandfather.
The Taylor-von Neumann-Sedov method 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), gasoline density (ρ), and a gas-dependent parameter (C).
To get a solution, astronomers turned to equations that have been found within the Forties, when scientists have been looking for methods to research 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 ability of his evaluation. Amazingly, the Taylor-von Neumann-Sedov method describes atomic-bomb shocks with radii of a whole bunch of meters, supernova shocks that stretch throughout gentle years, and tin-plasma shocks simply millimeters huge. All of them signify the identical primary bodily scenario: a compact, freestanding physique releasing vitality towards minimal resistance, increasing quickly right into a gaseous surrounding.
Early atomic explosions, similar to this take a look at on the Trinity Web site 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 method to the H-alpha photographs 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 concept and apply, nevertheless. In our EUV sources, we noticed that the H-alpha emission shouldn’t be 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 a variety of totally different parameters to study extra in regards to the blasts (a sort of experiment that’s clearly not potential for supernovas). As an illustration, we mapped blast-wave trajectories as a perform of ambient strain, droplet measurement, laser vitality, and goal form.
Our outcomes helped us to refine our fashions and to find out the easiest way to tailor the hydrogen atmosphere 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 have been impressed by astronomy. For hundreds of years, researchers have designed laboratory experiments and measurement strategies 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 potential.
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 manner as properly. As the foundations of atomic physics and the absorption strains of gases have 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, often known as Sort Ia. This sort of supernova is believed to happen when a white dwarf star pulls materials from a neighboring companion star till it reaches a vital mass and implodes, leading to a violent self-destruction. Sort Ia supernovas explode in a extremely constant manner, making them invaluable “commonplace candles” with predictable intrinsic luminosities: Evaluating their obvious brightness to their true, intrinsic luminosity makes it potential to measure their distances from us precisely throughout billions of sunshine years. These supernovas are getting used to review the growth of the universe, they usually have led to the startling discovery that the growth of the cosmos is accelerating.
In our EUV sources, we likewise goal 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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