An In-Depth Look at the Viability of X-rays as an Alternative to EUV Lithography

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On October 28th 2025, Substrate emerged from stealth with $100M in funding and a $1B valuation. The California startup has demonstrated proof-of-concept lithography tools competitive with ASML and fabs like TSMC, Intel and Samsung capable of leading edge nodes at potentially a fraction of the cost. The specific interest centers on X-ray lithography (XRL) as a successor to extreme ultraviolet (EUV) lithography used in today’s leading chip technologies.

This matters because TSMC, Samsung, and hopefully Intel, are the only foundries capable of mass-producing chips at the leading edge and ASML is the sole provider of lithography tools capable of producing these advanced nodes. Already, most American major fabless companies heavily rely on TSMC to manufacture their chips. Substrate’s technology might change all that. America once led chip manufacturing but ceded that position to Taiwan over decades of policy decisions. Substrate’s success means that America “will lead again” in chip manufacturing — if the technology actually pans out at scale.

To be clear, I actually have no idea if this will work, if Substrate’s claims are actually true, or how skeptical one has to be. Take any drastic claims with a healthy grain of salt, because, as Substrate’s CEO James Proud has said himself, this is an incredibly difficult problem but an extremely important one.

This article is intended to provide a better understanding of XRL as a logical successor to EUV. To provide context, we will start with the basics of lithography and trace its evolution so that the need for XRL is clear. Then, we will discuss the challenges and benefits of XRL, and conclude with some thoughts on Substrate.

Here is an outline:

• Photolithography and optical masks

• Wavelength and Aperture for photolithography

• EUV lithography

• X-ray lithography and Substrate

• X-ray sources

• Challenges in X-ray