China plans giant particle accelerator

Currently, only ASML holds exclusive ownership of the technology and, therefore, has a dominant position in the market. As of the end of 2022, ASML has successfully delivered 180 EUV systems, and according to a Bloomberg report published in April, it plans to ship an additional 60 EUVs this year.

To this end, some nations, like China, are working on ways to attempt to compete. And this is where researchers at Tsinghua University come into play. “One of the potential applications of our research is as a light source for future EUV lithography machines. I think this is why the international community is paying close attention,” explained project leader Professor Tang Chuanxiang from Tsinghua University.

ASML's current method uses an EUV light source generated using a laser-produced plasma technology. These powerful laser pulses are directed at tiny liquid droplets of tin, causing them to collapse and emit EUV pulse light upon impact. The resulting EUV light source generates approximately 250W of power after undergoing rigorous filtration and focusing processes.

When the EUV beam reaches the chip, it has already undergone reflection from 11 mirrors, which causes approximately a 30% energy loss at each point. Consequently, the beam's power is less than 5W when it finally reaches the wafer. This may become problematic as manufacturing advances to 3nm or 2nm.

On the other hand, Chuanxiang and his team's innovative SSMB technology generates higher terminal power with fewer mirrors needed due to its narrow bandwidth. This is achieved by utilizing the energy released by charged particles to produce a narrow bandwidth of continuous pure EUV light with a small scattering angle. Accelerated charged particles emit light, making accelerators one of the brightest artificial light sources.

“The main challenge lies in guiding the distribution of electrons within the storage ring of the accelerator, causing them to achieve collective synchronous radiation. The device could produce high-quality radiations from terahertz waves at a wavelength of 0.3mm to EUV waves at wavelengths of 13.5nm,” Zhao said in an academic report at Tsinghua in October 2022.

“Unlike free-electron lasers, which produce pulsed lasers with high peak power, SSMB sources produce continuous light with high average power,” he said.

Just the beginning

“There is still a long way to go before our independent development of EUV lithography machines, but SSMB-based EUV light sources give us an alternative to the sanctioned technology,” Zhao explained. “It requires continuous technological innovation based on SSMB EUV light sources and cooperation with upstream and downstream industries to build a usable lithography system," he added.