Free-Electron Laser Technology Aims to Cut EUV Source Costs by 50%

Free-electron lasers (FELs) and particle accelerators are not new. For years, companies, research institutions, and universities have owned and operated these systems to produce subatomic particles such as protons and neutrons, typically for physics and other scientific fields. An FEL is essentially a high-power light source that uses electrons to generate light at various wavelengths. The principle involves passing electrons, travelling close to the speed of light, through a periodic magnetic field to produce laser light; the wavelength can be tuned by adjusting the magnetic field frequency or the electron velocity.

US startup xLight is applying FEL technology to develop EUV light sources. Pat Gelsinger, former CEO of Intel, serves as the company's executive chairman. xLight's technology injects electrons into a particle accelerator, which then feeds into a free-electron laser to produce a coherent, high-intensity beam. The company claims its FEL source is four times more powerful than existing LPP devices, cutting per-wafer costs by approximately 50%, generating billions of dollars in additional revenue per scanner each year, supporting up to 20 ASML systems per unit, and offering a service life of up to 30 years.

On the technical side, conventional EUV lithography uses a 13.5nm wavelength because tin plasma efficiently produces light in that band. An FEL, by contrast, adjusts the output wavelength by varying the electron beam energy, undulator period, and magnetic field strength, theoretically covering wavelengths from soft X-rays to longer bands. Comparative data show that an LPP source requires about 4.4MW of electricity to produce 1kW of usable EUV, translating to an overall efficiency of roughly 0.05%. In contrast, an advanced energy-recovery FEL (ERL-FEL) needs only 0.7MW, making it about six times more efficient.

Despite the performance advantages of FELs in light-source output, industrial lithography demands high power, high stability, high repetition rates, high reliability, and low cost, among other conditions. ASML's existing EUV light sources, after years of engineering, have formed a complete industrial ecosystem. FELs typically require large electron accelerators, undulators, vacuum systems, and other components, resulting in enormous equipment size and cost. Furthermore, shorter wavelengths make it increasingly difficult to solve problems related to optical systems, masks, and photoresists. Beyond FELs, other technologies under discussion include high-harmonic generation (HHG), discharge-produced plasma (DPP), and synchrotron radiation, but all face challenges such as uncertain timelines.