The Semiconductor Industry's Most Important Tool Goes Green

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In the complex quest to keep increasing the density of transistors, extreme ultraviolet (EUV) lithography is the most critical tool. Costing more than US $100 million, these trailer-size systems bounce near x-ray wavelength light off a complex cascade of mirrors and onto silicon wafers to create patterns with nanometer-scale precision. Because the system's 13.5-nanometer light is absorbed by air, the whole mechanism exists in a vacuum. Well, almost.

spectrum.ieee.org/, Jun. 12, 2023 – 

There are enough contaminants in the system and the process that the machine needs several fine flows of hydrogen to sweep away anything that could muck up its delicate optics. These flows blow through about 600 liters of the gas per minute, with that amount likely to rise in the future.

Today, the resulting contaminated hydrogen is usually burned to form water. So the supply must constantly be replenished with new hydrogen. The problem is that most hydrogen is not made using green energy–it's made by processing natural gas with steam, releasing carbon dioxide both in the chemical process and from whatever energy source produced the steam. In an effort to lower EUV's environmental footprint and its cost of ownership, engineers at Edwards, an England-based vacuum systems firm, came up with a way to recycle as much as 80 percent of the gas.

Wanting to recover the hydrogen "is a bit of a no-brainer," says Anthony Keen, a technology manager at Edwards. "You could turn it into electricity, which is a nice, green, circular thing. But you'd still be consuming 100 percent of your resource. To clean up the hydrogen and send it back to the machine is actually the most effective."

Hydrogen flows in several parts of the EUV machine. For example, a curtainlike flow acts as a barrier between most of the optics and the silicon wafer, which at that stage is coated in photo-active chemicals that could contaminate the chamber. But the bulk of the hydrogen, and the focus of Edwards's hydrogen recovery system, is used in the EUV light source. Here, kilowatt-class lasers zap droplets of molten tin in midflight, blasting them into plasma that glows with EUV. The hydrogen flow keeps vaporized tin from mucking up the system's optics. It's also important in carrying away the scorching heat of the plasma generation.

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