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

However an unconventional various is within the works. A bunch of researchers on the
Excessive Vitality Accelerator Analysis Group, often known as KEK, in Tsukuba, Japan, is betting EUV lithography could be cheaper, faster, and extra environment friendly if it harnesses the ability 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 strong mild supply referred to 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 power 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 slim spectral width, and different options make it appropriate as an utility for future lithography,”
Norio Nakamura, researcher in superior mild sources at KEK, advised me on a go to to the ability.

Linacs Vs. Laser-Produced Plasma

Right this moment’s EUV programs 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 trade was determined for them. Chipmakers had been getting by with workaround after workaround for the then most superior system, lithography utilizing 193-nm mild. Shifting to a a lot shorter, 13.5-nm wavelength was a revolution that might collapse the variety of steps wanted in chipmaking and permit Moore’s Regulation to proceed effectively into the following decade.

The
chief explanation for the continuous delays was a light-weight supply that was too dim. The know-how that finally delivered a vibrant sufficient supply of EUV mild is known as laser-produced plasma, or EUV-LPP. It employs a carbon dioxidelaser to blast molten droplets of tin into plasma 1000’s of instances per second. The plasma emits a spectrum of photonic power, and specialised optics then seize the required 13.5-nm wavelength from the spectrum and information it by way of a sequence of mirrors. Subsequently, the EUV mild is mirrored off a patterned masks after which projected onto a silicon wafer.

The experimental compact power restoration linac at KEK makes use of a lot of the power 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 mild 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 gradual. And pushing too onerous for velocity can result in pricey errors.

When the machines had been first launched, the ability degree 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 collection of machines.

ASML’s present mild 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 mild supply. But it surely might be troublesome to realize, 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.

Tough however not essentially not possible. Doubling the supply energy is “very difficult,” agrees
Ahmed Hassanein who leads the Middle for Supplies Below Excessive Atmosphere, at Purdue College, in Indiana. However he factors out that ASML has achieved equally troublesome targets prior to now utilizing an built-in strategy of enhancing 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 situation ASML faces with laser-produced plasma sources. “There are a variety of difficult points in upgrading to greater 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 downside. These programs eat some 600 liters of hydrogen fuel per minute, most of which works into retaining tin and different contaminants from getting onto the optics and wafers. (Recycling, nonetheless, might scale 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 growing, might be as a lot as 10 to 100 instances as environment friendly, he says.

The Vitality Restoration Linear Accelerator

The system KEK is growing generates mild by boosting electrons to relativistic speeds after which deviating their movement in a specific method.

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 referred to as an undulator, a collection of oppositely oriented magnets. (The KEK system presently has two.) The undulators pressure the dashing electrons to observe a sinusoidal path, and this movement causes the electrons to emit mild.

What occurs subsequent is a phenomenon referred to as
self-amplified spontaneous emissions, or SASE. The sunshine interacts with the electrons, slowing some and dashing up others, in order 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 section with the interval of those microbunches, producing a coherent beam of laser mild.

It’s at this level that KEK’s compact power 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 is 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 section to newly injected electrons which are simply beginning their journey. The result’s that the spent electrons switch a lot of their power to the brand new beam, boosting its power. As soon as the unique electrons have had a few of their power drained away like this, they’re diverted right into a beam dump.

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

Different specialists 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 Vitality 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 might be achieved by some storage ring-based synchrotrons—big round accelerators that preserve a beam of electrons transferring with a continuing kinetic power. So, the KEK researchers went in the hunt for a extra acceptable utility. After speaking with Japanese tech firms, together with Toshiba, which had a flash reminiscence chip division on the time, the researchers performed an preliminary examine that confirmed {that a} kilowatt-class mild 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 begin the journey to EUV mild.

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 vast with a lot of the house taken up by a bewildering tangle of complicated gear, pipes, and cables that snakes alongside each side of its size within the type of an elongated racetrack.

The accelerator is just not but capable of generate EUV wavelengths. With an electron beam power of 17 megaelectronvolts, the researchers have been capable of generate SASE emissions in bursts of 20-micrometer infrared mild.
Early take a look at outcomes had been revealed within the Japanese Journal of Utilized Physics in April 2023. The following step, which is underway, is to generate a lot higher laser energy in continuous-wave mode.

To make sure, 20 micrometers is a far cry from 13.5 nanometers. And there are already kinds 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, mild depth will increase proportionally to the variety of injected electrons. By comparability, in free-electron laser programs, mild 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 gear upgrades past what KEK presently has room for. So, the researchers at the moment are making the case for setting up a brand new prototype system that may produce the wanted 800 MeV.

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

In 2021, earlier than extreme inflation affected economies across the globe, the KEK workforce estimated the development price (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 latest inflation under consideration, “the estimated prices per publicity device in our setup are nonetheless fairly 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 must develop new editions of key parts such because the superconducting cavity, the electron gun, and the undulator. Engineers may also need to develop good procedural strategies to make sure, for example, that the electron beam doesn’t degrade or falter throughout operations.

And to make sure their strategy is price 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 might convey the EUV mild to a number of publicity instruments with out important lack of energy or harm to the mirrors.

Different EUV Potentialities

It’s too early within the improvement 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 also be amongst these chasing it. The corporate, which is filled with particle-accelerator veterans from the Stanford Linear Accelerator and elsewhere, lately inked an R&D take care of 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 introduced 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 may require critical funding and take appreciable time.”

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

Extra importantly, Benson warns that and not using a forthcoming dedication to put money into the know-how, “improvement of EUV-FELs may not are available in time to assist the semiconductor trade.”