Scientists plan to build particle accelerator to power giant chip factory

Scientists are exploring new ways to get around limitations on the lithography machines used to produce microchips. Researchers are using particle accelerators to create new laser sources that could lay the foundation for the future of semiconductor manufacturing.

Plans are underway to build a particle accelerator with a circumference between 100 and 150 meters (328 and 492 feet), about the size of two basketball courts. The accelerator's electron beam will be transformed into a high-quality light source for on-site chip manufacturing and scientific exploration.

The Tsinghua University team is in active discussions with the Xiongan New Area authorities to select a construction site for this cutting-edge project.

In contrast to commercial companies such as Advanced Semiconductor Materials Lithography (ASML), which tend to downsize their exported chipmaking machines, the Chinese project aims to localize manufacturing by building a large factory housing multiple lithography machines around a single accelerator.

The innovation could facilitate high-volume, low-cost chip manufacturing and could potentially propel China into a leadership role in industrial production of advanced chips, known as 2nm (nanometer) chips and others.

Lithography systems are among the most complex machines ever created by humans. Currently, ultra-short wavelength extreme ultraviolet light (EUV) is widely used in the production of 7nm and below node chips.

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

While many researchers are pursuing this technology, Chinese scientists have been exploring a different path. The project has been running since 2017 but only recently came into public view due to Huawei's breakthroughs in chip manufacturing.

"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." Project leader Tang Chuanxiang, a professor at Tsinghua University, said in a report on the Tsinghua University website.

Since the focus on the project has affected their normal scientific research, Tang's team has stopped accepting interviews.

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

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

"The main challenge is to guide the distribution of electrons within the accelerator storage ring so that they achieve collective synchrotron radiation. The device can produce high-quality radiation from terahertz waves with a wavelength of 0.3 millimeters to extreme ultraviolet waves with a wavelength of 13.5 nanometers." Zhao Said in an academic report at Tsinghua University in October 2022.
"Unlike free electron lasers, which produce pulsed laser light with high peak power, SSMB light sources produce continuous light with high average power," he said.

This characteristic leads to broad application prospects of SSMB.

Compared with current ASML EUV technology, SSMB is a more ideal light source. It has higher average power and higher chip yield and lower unit cost.
ASML uses laser-generated plasma to create an EUV light source, projecting intense laser pulses onto tiny droplets of liquid tin. The laser shatters the droplets and generates pulses of EUV 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 is reflected by 11 mirrors, each of which causes about 30% energy loss. Therefore, the power of the beam reaching the wafer is less than 5W. This may become an issue when manufacturing moves to 3nm or 2nm.

SSMB technology avoids such problems. The SSMB beam achieves a higher output power of 1000W and, due to its narrower bandwidth, requires fewer mirrors, naturally resulting in higher terminal power.

Zhao proposed this theory in 2010. Subsequently, in 2017, Tang formed a dedicated team at Tsinghua University.

The team conducted the first validation phase at the Metrology Light Source (MLS) in Berlin, Germany. In 2019, the experiment was successful, and they published a paper in 2021 in the peer-reviewed journal Nature to illustrate the phenomenon.

Then in 2022, the team designed another prototype at Tsinghua University.
"Tsinghua University has designed the SSMB-EUV light source with a designed EUV power higher than 1kW, and some key technologies are close to maturity." Professor Pan Zhilong, a team member, said in a speech at an academic seminar in January 2022.

In February this year, the Hebei Provincial Department of Science and Technology held a special meeting in Xiongan to study how to cultivate technology enterprises in the new area. Mr. Pan attended the meeting, further demonstrating the team’s efforts to advance SSMB into industry practice.

At the meeting, Teacher Pan introduced the planning of Tsinghua University’s SSMB-EUV project. The team also came to Xiongan to select sites for future construction.
The establishment of chip factories depends on funding and other engineering details. But more importantly, new ideas may lead to new technological routes.
Since the progress of the project has not yet been disclosed to the public, Tang expects the team and the industry to make further efforts to help small and medium-sized enterprises develop.

"As a new light source, this technology has been experimentally verified. But it is necessary to establish a solid-state SSMB light source research device operating in the EUV band," Tang said in the Nature paper.
"We can then educate scientific and industrial users [with the device] and refine the SSMB technology," he said.

Tang believes that the technology can help China escape future sanctions, but he did not talk about the specific progress of SSMB-based lithography machines.
"We still have a long way to go to develop our own EUV lithography machines, but SSMB-based EUV light sources provide us with an alternative to recognized technologies," he said in the Tsinghua report.
"It is necessary to continuously carry out technological innovation based on the SSMB EUV light source and cooperate with upstream and downstream industries to build a usable lithography system."

Tang also pointed out in the paper that the realization of SSMB-EUV light source will provide new tools for cutting-edge research in materials science, basic physics, biochemistry and other disciplines.

Source: Laser Network