How Does EUV Lithography Affect PCB Design—and National Security?February 06, 2020 by Robin Mitchell
The US government has blocked the sale of an EUV lithography system to China. What is EUV? why is it important? and why did the US government prevent its sale to China?
Reuters recently reported how the US government launched an "extensive campaign to block the sale of Dutch chip manufacturing technology to China."
That technology? An EUV (Extreme Ultraviolet) lithography system.
This buzz surrounding EUV gives us the opportunity to discuss what EUV lithography is, why it is important, and why, according to Reuters, the US government campaigned to prevent its sale to China.
How Does EUV Lithography Work?
Extreme Ultraviolet (EUV) lithography is used to image the individual layers of silicon devices. When creating features in silicon, the smallest size that can be achieved is dependent on many factors.
One factor is the wavelength of light used to expose photoresist layers. While this factor was not a concern in the earliest semiconductor devices, where the wavelength of light would be significantly smaller than feature sizes, modern semiconductor devices have feature sizes that are in the tens of nanometers.
Silicon wafer with a mask or reticle on top; ASML describes a lithography system as a "light projector." Image used courtesy of ASML
Such small features require a reduction in the wavelength of the exposing light source, which itself presents problems. These problems include difficulty in repeatability, loss of resolution, and damaging effects of the exposing light source.
Not only does EUV allow for sub 10 nm silicon features; it also works in a fundamentally different method than standard lithography methods.
EUV masks are made of multiple layers of Mo or Si mirrors (up to 40) that are stacked beneath an Ru layer. On top of the Ru layer is the design work (made from an abortive material), and this layer is topped with an anti-reflective coating.
Now, instead of light being shone through the mask, it is instead hit with the EUV light at an angle of 6°, which reflects off the internal Mo/Si mirror layers and exits the structure onto the silicon wafer. Areas that are to be patterned absorb the reflected light from the internal mirror layers, preventing the resist from hardening.
The Prevented Sale
Reuters journalists Alexandra Alper, Toby Sterling, and Stephen Nellis stated that in 2018, ASML was approached by a Chinese customer for an EUV lithography machine. The Dutch government approved the sale, providing ASML an export license. However, when the US government was made aware of this deal, they started a campaign to block the exportation of the EUV machine to the Chinese.
EUV engineers look into a mid-module assembly work center. Image used courtesy of ASML
Following the US' 2020 campaign, the Dutch government revoked the export license from ASML. This means that the EUV machine cannot be shipped to Chinese manufacturers.
But does this thwarted deal only postpone an inevitable transfer of this technology?
Who Has Access to EUV Lithography?
There are fewer than fifty systems that currently employ EUV worldwide. Other technologies such as DUV (Deep Ultraviolet) are widely supported by the majority of fabrication houses. However, other technologies do not offer feature sizes as small as what EUV can achieve; DUV enables up to 100 nm while EUV can be used for features down to 7 nm.
Rendering of the inside of ASML's EUV machine. Image used courtesy of ASML
This means that EUV-based technology can have far more transistors per unit area, allowing more complex circuitry and therefore processing power.
Only recently has Samsung and TSMC entered the production stage with EUV technology creating silicon devices. According to ASML, the technology used to create masks still requires improvement because devices made using the EUV method have had low yields.
However, this has not stopped Huawei producing a 5G version of their Kirin 990 chip, whose construction was outsourced to TSMC using a 7 nm process. Samsung is utilizing EUV technology in their next-generation mobile processors, the Exynos 990 and Exynos Modem 5123, to incorporate 5G, AI, and create faster processors.
How Does EUV Technology Affect PCB Design?
What makes EUV lithography special is its capability to increase the number of transistors per unit area by reducing transistor features, such as the size of the gate, junctions, and the interconnecting metal layers.
The reduction in transistor size allows designers to either reduce the physical size of a chip (thereby reducing PCB sizes) or to increase the processing power of that chip. This reduction in transistor size will be pivotal in next-generation electronics, including mobile, edge-computing devices, and general data processing.
EUV lithography system. Image used courtesy of ASML
Edge computing and mobile technologies are putting pressure on local devices to not only have strong security features and increased generic computational power but also to have dedicated hardware for running AI algorithms.
Reduced transistor sizes will allow for the same-sized chips to integrate the CPU, security peripherals, and AI processors all onto a single chip, making those devices not only more powerful but also more intelligent.
National Security and EUV
The US state department has, in the past, explained why they have attempted to block certain technologies from China.
In a September 2019 address, Dr. Christopher Ashley Ford, Assistant Secretary of the Bureau of International Security and Nonproliferation stated, "China’s strategy of systematic technology acquisition and diversion exemplifies the close relationship and nearly indistinguishable status . . . between its own companies and the Chinese government."
Ford expressed concerns that China's access to powerful technology—in this case, a technology that creates the world's most powerful chips—gives the country an edge in important subfields of electronic design, including cybersecurity and defense.
An EUV lithography machine, like the one from ASML, certainly has the ability to generate high-transistor devices, which are key components in both military devices and cyberattacks.
EUV lithography will allow for silicon fabrication houses to further reduce the size of transistors and increase the power of everyday silicon devices. For instance, integrating AI into mobile tech is a major driving force for such technology. But like all next-generation technology, suppliers and regulatory agencies must deploy this technology with care.
Do you see the race for smaller, more powerful chips as a modern-day Space Race? Why or why not? Share your thoughts in the comments below.