ASML snubs Elon Musk-backed particle accelerator chipmaking tech — firm doubles down on 1,000W laser-produced plasma systems for chipmaking tools

One of the key challenges with the development of extreme ultraviolet (EUV) lithography scanners is building a powerful and reliable light source. ASML, which is the only company to manufacture EUV lithography tools, uses rather complicated laser-produced plasma (LPP) technology to generate EUV light. By contrast, numerous companies propose to use a free-electron laser (FEL), which relies on a particle accelerator, for EUV generation. While FEL has its advantages and is even endorsed by Elon Musk, ASML is unlikely to adopt it, according to JPMorgan.

"Given laser advances, ASML sees no reason to try new 'FEL' light source favored by Musk," reports Semi Doped, citing a JPMorgan note for clients.

Modern EUV lithography systems use laser-produced plasma light sources that fire powerful CO₂ laser pulses at tiny droplets of molten tin, around 30 microns in diameter, which turns them into ionized plasma with electron temperatures of several tens of electron volts that emits 13.5-nm EUV radiation. The light is then collected by a roughly 0.5-meter elliptical collector mirror coated with multiple layers of molybdenum and silicon, which selectively reflects as much 13.5-nm radiation as possible and directs it toward the intermediate focus at the entrance to the scanner.

Since virtually all materials absorb EUV radiation — even specialized multilayer mirrors absorb a substantial portion of it — the entire optical path must operate in vacuum and use reflective rather than conventional refractive optics, which is one reason why generating sufficient EUV source power remains challenging.

Despite major challenges, ASML has gradually increased the source power of its LPP light sources from around 250W to around 500W and plans to increase it to 1000W in the coming years. In addition, the company plans to almost double the number of generated tin droplets to 100,000 every second.

A free-electron laser (FEL) generates EUV light by accelerating electrons to nearly the speed of light and passing the electron beam through an undulator, a series of alternating magnets that force electrons to oscillate and emit radiation. Interaction between the electrons and their radiation causes them to form microscopic bunches and emit light with a 13.5-nm wavelength. This approach eliminates tin droplets and associated debris (that require usage of protective pellicles on photomasks) as well as potentially provides substantially higher EUV power than LPP sources. Furthermore, one FEL can potentially replace multiple LPP sources with a single FEL and a large EUV beam-distribution system.

Yet, there is a major tradeoff: instead of a relatively compact LPP, FEL requires a highly complex particle accelerator, an electron source, a long undulator, electron-beam control, radiation shielding, and an extremely complex distribution system featuring mirrors capable of handling and distributing very high EUV power without losing too much of it along the way. The whole machine must achieve semiconductor fab levels of availability, efficiency, and cost, something that took ASML and the rest of the industry years to achieve.

So, while there is a great enthusiasm surrounding FEL in China, the U.S., and Japan, it will likely take a decade, if not more, before FEL will be able to rival LPP in real semiconductor production facilities. The technology will likely devour billions of dollars in the meantime, so not all entities currently pursuing FEL will live that long.