EUV Gentle Supply: Is the Future in a Particle Accelerator?

However an unconventional different is within the works. A gaggle of researchers on the
Excessive Power Accelerator Analysis Group, referred to as KEK, in Tsukuba, Japan, is betting EUV lithography could be cheaper, faster, and extra environment friendly if it harnesses the facility of a particle accelerator.

Even earlier than the primary EUV machines had been put in in fabs, researchers noticed potentialities for EUV lithography utilizing a robust gentle supply known as a
free-electron laser (FEL), which is generated by a particle accelerator. Nonetheless, not simply any particle accelerator will do, say the scientists at KEK. They declare the most effective candidate for EUV lithography incorporates the particle-accelerator model of regenerative braking. Generally known as an vitality restoration linear accelerator, it might allow a free electron laser to economically generate tens of kilowatts of EUV energy. That is greater than sufficient to drive not one however many next-generation lithography machines concurrently, pushing down the price of superior chipmaking.

“The FEL beam’s excessive energy, its slender spectral width, and different options make it appropriate as an software for future lithography,”
Norio Nakamura, researcher in superior gentle sources at KEK, instructed me on a go to to the power.

Linacs Vs. Laser-Produced Plasma

Right this moment’s EUV methods are made by a single producer,
ASML, headquartered in Veldhoven, Netherlands. When ASML launched the primary era of those US $100-million-plus precision machines in 2016, the business was determined for them. Chipmakers had been getting by with workaround after workaround for the then most superior system, lithography utilizing 193-nm gentle. Shifting to a a lot shorter, 13.5-nm wavelength was a revolution that will collapse the variety of steps wanted in chipmaking and permit Moore’s Regulation to proceed nicely into the following decade.

The
chief reason behind the continuous delays was a light-weight supply that was too dim. The know-how that finally delivered a shiny sufficient supply of EUV gentle known as laser-produced plasma, or EUV-LPP. It employs a carbon dioxide laser to blast molten droplets of tin into plasma hundreds of occasions per second. The plasma emits a spectrum of photonic vitality, and specialised optics then seize the mandatory 13.5-nm wavelength from the spectrum and information it by a sequence of mirrors. Subsequently, the EUV gentle is mirrored off a patterned masks after which projected onto a silicon wafer.

The experimental compact vitality restoration linac at KEK makes use of many of the vitality from electrons on a return journey to hurry up a brand new set of electrons.KEK

All of it provides as much as a extremely complicated course of. And though it begins off with kilowatt-consuming lasers, the quantity of EUV gentle that’s mirrored onto the wafer is simply a number of watts. The dimmer the sunshine, the longer it takes to reliably expose a sample on the silicon. With out sufficient photons carrying the sample, EUV can be uneconomically sluggish. And pushing too laborious for velocity can result in pricey errors.

When the machines had been first launched, the facility stage was sufficient to course of about 100 wafers per hour. Since then, ASML has managed to steadily hike the output to about 200 wafers per hour for the current sequence of machines.

ASML’s present gentle sources are rated at 500 watts. However for the even finer patterning wanted sooner or later, Nakamura says it might take 1 kilowatt or extra. ASML says it has a highway map to develop a 1,000-W gentle supply. But it surely may very well be troublesome to attain, says Nakamura, who previously led the beam dynamics and magnet group at KEK and got here out of retirement to work on the EUV venture.

Troublesome however not essentially unimaginable. Doubling the supply energy is “very difficult,” agrees
Ahmed Hassanein who leads the Heart for Supplies Underneath Excessive Surroundings, at Purdue College, in Indiana. However he factors out that ASML has achieved equally troublesome targets previously utilizing an built-in method of bettering and optimizing the sunshine supply and different parts, and he isn’t ruling out a repeat.

In a free electron laser, accelerated electrons are topic to alternating magnetic fields, inflicting them to undulate and emit electromagnetic radiation. The radiation bunches up the electrons, resulting in their amplifying solely a selected wavelength, making a laser beam.Chris Philpot

However brightness isn’t the one challenge ASML faces with laser-produced plasma sources. “There are a selection of difficult points in upgrading to increased EUV energy,” says Hassanein. He rattles off a number of, together with “contamination, wavelength purity, and the efficiency of the mirror-collection system.”

Excessive working prices are one other drawback. These methods devour some 600 liters of hydrogen gasoline per minute, most of which matches into conserving tin and different contaminants from getting onto the optics and wafers. (Recycling, nonetheless, might cut back this determine.)

However finally, working prices come all the way down to electrical energy consumption. Stephen Benson, lately retired senior analysis scientist on the Thomas Jefferson Nationwide Accelerator Facility, in Virginia., estimates that the wall-plug effectivity of the entire EUV-LPP system could be lower than 0.1 p.c. Free electron lasers, just like the one KEK is creating, may very well be as a lot as 10 to 100 occasions as environment friendly, he says.

The Power Restoration Linear Accelerator

The system KEK is creating generates gentle by boosting electrons to relativistic speeds after which deviating their movement in a specific means.

The method begins, Nakamura explains, when an electron gun injects a beam of electrons right into a meters-long cryogenically cooled tube. Inside this tube, superconductors ship radio-frequency (RF) indicators that drive the electrons alongside quicker and quicker. The electrons then make a 180-degree flip and enter a construction known as an undulator, a sequence of oppositely oriented magnets. (The KEK system at the moment has two.) The undulators pressure the rushing electrons to observe a sinusoidal path, and this movement causes the electrons to emit gentle.

What occurs subsequent is a phenomenon known as
self-amplified spontaneous emissions, or SASE. The sunshine interacts with the electrons, slowing some and rushing up others, so that they collect into “microbunches,” peaks in density that happen periodically alongside the undulator’s path. The now-structured electron beam amplifies solely the sunshine that’s in part with the interval of those microbunches, producing a coherent beam of laser gentle.

It’s at this level that KEK’s compact vitality restoration linac (cERL), diverges from lasers pushed by typical linear accelerators. Ordinarily, the spent beam of electrons is disposed of by diverting the particles into what known as a
beam dump. However within the cERL, the electrons first loop again into the RF accelerator. This beam is now within the reverse part to newly injected electrons which can be simply beginning their journey. The result’s that the spent electrons switch a lot of their vitality to the brand new beam, boosting its vitality. As soon as the unique electrons have had a few of their vitality drained away like this, they’re diverted right into a beam dump.

“The acceleration vitality within the linac is recovered, and the dumped beam energy is drastically decreased in comparison with [that of] an strange linac,” Nakamura explains to me whereas scientists in one other room function the laser. Reusing the electrons’ vitality implies that for a similar quantity of electrical energy the system sends extra present by the accelerator and may fireplace the laser extra regularly, he says.

Different consultants agree. The energy-recover linear accelerator’s improved effectivity can decrease prices, “which is a serious concern of utilizing EUV laser-produced plasma,” says Hassanein.

The Power Restoration Linac for EUV

The KEK compact energy-recovery linear accelerator was initially constructed between 2011 and 2013 with the intention of demonstrating its potential as a synchrotron radiation supply for researchers working for the establishment’s physics and materials-science divisions. However researchers had been dissatisfied with the deliberate system, which had a decrease efficiency goal than may very well be achieved by some storage ring-based synchrotrons—big round accelerators that preserve a beam of electrons transferring with a relentless kinetic vitality. So, the KEK researchers went in the hunt for a extra acceptable software. After speaking with Japanese tech firms, together with Toshiba, which had a flash reminiscence chip division on the time, the researchers performed an preliminary research that confirmed {that a} kilowatt-class gentle supply was doable with a compact energy-recovery linear accelerator. And so, the EUV free-electron-laser venture was born. In 2019 and 2020, the researchers modified the present experimental accelerator to start out the journey to EUV gentle.

The system is housed in an all-concrete room to guard researchers from the extreme electromagnetic radiation produced throughout operation. The room is a few 60 meters lengthy and 20 meters extensive with a lot of the area taken up by a bewildering tangle of complicated tools, pipes, and cables that snakes alongside either side of its size within the type of an elongated racetrack.

The accelerator is just not but in a position to generate EUV wavelengths. With an electron beam vitality of 17 megaelectronvolts, the researchers have been in a position to generate SASE emissions in bursts of 20-micrometer infrared gentle.
Early check outcomes had been printed within the Japanese Journal of Utilized Physics in April 2023. The following step, which is underway, is to generate a lot better laser energy in continuous-wave mode.

To make sure, 20 micrometers is a far cry from 13.5 nanometers. And there are already forms of particle accelerators that produce synchrotron radiation of even shorter wavelengths than EUV. However lasers based mostly on energy-recovery linear accelerators might generate considerably extra EUV energy as a result of their inherent effectivity, the KEK researchers declare. In synchrotron radiation sources, gentle depth will increase proportionally to the variety of injected electrons. By comparability, in free-electron laser methods, gentle depth will increase roughly with the sq. of the variety of injected electrons, leading to rather more brightness and energy.

For an energy-recovery linear accelerator to succeed in the EUV vary would require tools upgrades past what KEK at the moment has room for. So, the researchers at the moment are making the case for developing a brand new prototype system that may produce the wanted 800 MeV.

An electron gun injects cost into the compact vitality restoration linear accelerator at KEK.KEK

In 2021, earlier than extreme inflation affected economies across the globe, the KEK workforce estimated the development value (excluding land) for a brand new system at 40 billion yen ($260 million) for a system that delivers 10 kW of EUV and provides a number of lithography machines. Annual working prices had been judged to be about 4 billion yen. So even taking current inflation under consideration, “the estimated prices per publicity software in our setup are nonetheless slightly low in comparison with the estimated prices” for in the present day’s laser-produced plasma supply, says Nakamura.

There are many technical challenges to work out earlier than such a system can obtain the excessive ranges of efficiency and stability of operations demanded by semiconductor producers, admits Nakamura. The workforce should develop new editions of key parts such because the superconducting cavity, the electron gun, and the undulator. Engineers may also must develop good procedural strategies to make sure, as an illustration, that the electron beam doesn’t degrade or falter throughout operations.

And to make sure their method is value efficient sufficient to seize the eye of chipmakers, the researchers might want to create a system that may reliably transport greater than 1 kW of EUV energy concurrently to a number of lithography machines. The researchers have already got a conceptual design for an association of particular mirrors that will convey the EUV gentle to a number of publicity instruments with out vital lack of energy or injury to the mirrors.

Different EUV Potentialities

It’s too early within the growth of EUV free-electron lasers for quickly increasing chipmakers to pay it a lot consideration. However the KEK workforce is just not alone in chasing the know-how. A venture-backed startup
xLight, in Palo Alto, Calif. can be amongst these chasing it. The corporate, which is full of particle-accelerator veterans from the Stanford Linear Accelerator and elsewhere, lately inked an R&D cope with Fermi Nationwide Accelerator Laboratory, in Illinois, to develop superconducting cavities and cryomodule know-how. Makes an attempt to contact xLight went unanswered, however in January, the corporate took half within the eighth Workshop EUV-FEL in Tokyo, and former CEO Erik Hosler gave a presentation on the know-how.

Considerably, ASML thought-about turning to particle accelerators a decade in the past and once more extra lately when it in contrast the progress of free-electron laser know-how to the laser-produced plasma highway map. However firm executives determined LLP offered fewer dangers.

And, certainly, it’s a dangerous highway. Unbiased views on KEK’s venture emphasize that reliability and funding would be the greatest challenges the researchers face going ahead. “The R&D highway map will contain quite a few demanding phases in an effort to develop a dependable, mature system,” says Hassanein. “This can require severe funding and take appreciable time.”

“The machine design should be extraordinarily strong, with redundancy inbuilt,” provides retired analysis scientist Benson. The design should additionally make sure that parts are usually not broken from radiation or laser gentle.” And this should be completed “with out compromising efficiency, which should be adequate to make sure first rate wall-plug effectivity.”

Extra importantly, Benson warns that with no forthcoming dedication to put money into the know-how, “growth of EUV-FELs won’t are available time to assist the semiconductor business.”