Chip lithography with X-rays aims to challenge ASML and TSMC

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The start-up “Substrate” aims to lead the United States back to dominance in semiconductor manufacturing. To this end, Substrate plans to build complete semiconductor plants (fabs) that utilize a new, self-developed form of X-ray lithography. This is intended to be cheaper than the established EUV lithography technology, for which ASML produces machines used by TSMC, among others.

This cost advantage is intended to make chip manufacturing in the US economically viable and also strengthen its position against China.

Among Substrate's funders is Peter Thiel's Founders Fund, which is why the announcement attracted considerable attention.

Substrate CEO James Proud is said to lead a team of around 50 experts in semiconductor manufacturing and lithography. The company has so far revealed few technical details about its special X-ray lithography and has not provided a concrete timeline.

Substrate describes parts of the process on its website and publishes two micrographs of wafers showing structures that are said to be comparable to those from classic manufacturing methods of the 3 and 2 nanometer classes (N3/N2).

Accelerator instead of Plasma Sources

Substrate's “Advanced X-Ray Lithography” (Advanced XRL) is intended to use X-rays of an unspecified wavelength from a particle accelerator. The latter is built directly into the lithography machine, which also contains “a completely new optical system and a high-speed mechanical system.”

According to the company, Substrate is drawing on “decades of progress by American national laboratories” such as Lawrence Livermore (LLNL) and Stanford (SLAC), as well as artificial intelligence (AI), for the development of the particle accelerator.

In contrast, ASML's EUV lithography systems feature a complex source for soft X-rays with a wavelength of 13.5 nanometers, in which laser radiation excites a tin plasma.

Substrate also mentions that the lithography system processes 300-millimeter wafers and achieves very high acceleration values. Absolute values are again not specified, but for comparison: ASML's High-NA EUV systems' mirror masks (reticles) accelerate at around 32 g (314 m/s²) to enable the machines to expose more than 200 wafers per hour.

X-ray Lithography

There are different XRL approaches, such as the X-ray LIGA with synchrotron radiation developed at the former Karlsruhe Nuclear Research Center developed in 1982 at the former Karlsruhe Nuclear Research Center. Or Deep X-ray Lithography (DXRL), which was developed at the synchrotron Elettra in Trieste.

Companies like General Atomics are working on comparatively compact particle accelerators are working on comparatively compact particle accelerators for industry.

However, there are also approaches to use free-electron lasers (FELs) for semiconductor lithography. Researchers use the 3.4-kilometer-long X-ray laser European XFEL in Schenefeld near Hamburg, for example, for microstructural analysis.

Maskless Lithography?

Substrate does not mention exposure masks, which could indicate that it is about so-called maskless lithography. In this process, a narrowly focused beam writes the desired patterns directly onto the photoresist (Direct Write).

Electron beam lithography for chip production (E-Beam Lithography) has been under development for more than 20 years. It is considered too slow for mass production so far. So-called Multi Beam Mask Writers (MBMW) are used for the manufacturing of lithography masks and work with hundreds of thousands of electron beams simultaneously.

Radical Approach

It is not yet possible to assess whether Surface's ideas can be implemented in a reasonable timeframe. Such a radical approach is not entirely without precedent: the Japanese company Rapidus is also trying to conceive chip manufacturing in a completely different way than before.

(ciw)