An interesting article on China's chipbuilding efforts, including a proposal for a giant chip factory with a particle accelerator 100-150 meters in circumference, and a discussion of the physics behind it (which I get the gist of, I think).

ASML is the only company that owns the technology and therefore dominates the market. As of the end of 2022, ASML had delivered 180 EUV systems. It also plans to ship 60 EUVs this year, according to a Bloomberg report published in April.

While there are many researchers chasing the technology, the Chinese scientists have been exploring a different path. It is a project that has been running since 2017, but due to Huawei’s breakthroughs in chip manufacturing, it was recently catapulted into public view.

“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,” said project leader Professor Tang Chuanxiang from Tsinghua University in a report on the university’s website.

The theory behind the team’s research is a new luminescence mechanism called steady-state microbunching (SSMB). It was first proposed by Professor Zhao Wu at Stanford University and his student Daniel Ratner in 2010. Zhao is a former student of the famous physicist Yang Zhenning.

In short, SSMB theory uses the energy released by charged particles during acceleration to act as a light source. The result is a narrow bandwidth, small scattering angle and continuous pure EUV light. Charged particles emit light when they are accelerated, and accelerators that use this phenomenon are among the brightest artificial sources of light available.

“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. This characteristic has led to the broad application prospects of SSMB.

Compared with current ASML EUV technology, SSMB is a more ideal light source. It has a higher average power and higher chip production output with lower unit cost.

ASML creates an EUV source from laser-produced plasma, where strong laser pulses are projected to liquid microdroplets of tin. The laser crushes the droplets and produces EUV pulse light during the impact. After complex filtering and focusing, an EUV light source with a power of about 250W is produced.

Before reaching the chip, the EUV beam undergoes reflection from 11 mirrors, each causing about a 30 per cent energy loss. As a result, the power of the beam is less than 5W when reaching the wafer. This can become an issue when manufacturing turns to 3nm or 2nm. SSMB technology avoids such concerns. SSMB beams achieve a higher output power of 1000W, and due to its narrow bandwidth, fewer reflecting mirrors are needed, which naturally generates higher terminal power.