Accounting for sustainability in lithography

Like others at the 2025 Advanced Lithography + Patterning conference, Emily Gallagher, sustainability program director at imec, mentioned the exponential growth of AI demand, during a talk on Monday. Her focus was sustainability. During her presentation, she covered a particular consequence of that growing AI demand: the construction and operation of data centers.

“As we build these data centers, we are adding emissions,” she said.

Those emissions arise from the manufacturing of the chips within the centers as well as the power consumed by the semiconductors as they generate answers to queries. These emissions are Scope 1, which are direct as well as Scope 2 and 3. Scope 2 are emissions from energy purchased by an organization. Scope 3 are indirect emissions, such as those from suppliers.

Gallagher noted the emissions are not the only impact of data centers. There is water use and other factors to consider that influence the ability of the Earth to maintain environmental stability, resilience, and life-support functions. Exceeding these boundaries on a planetary scale, Gallagher said, means that the Earth is not at a safe operating point.

Avoiding such a situation and correcting it if it does happen is everyone’s job, Gallagher said. “We all have a role to play.”

To that end, imec offers software tools that analyze the life cycle impact of a chip. Armed with this information, chip makers and associated companies can take actions to address sustainability issues.  

For semiconductor manufacturing in general and lithography in particular, for example, Gallagher pointed out that one way to tackle such sustainability issues is to reduce the use of forever chemicals, those that stay present forever in the environment once released. Some gases, such as CF₄, used to etch layers during patterning fall into this category.

Gallagher reported on an investigation into reducing gas usage, which included development of a process recipe for etching. However, the new process took much longer than the previous one, and while its environmental impact was lower for the gas it was higher for electricity usage. Further work by the researchers refined the process steps, with the result being a significant decrease in gas use without other adverse sustainability impacts.

It's also possible to recycle unused gas and thereby improve sustainability. Gallagher recounted work done at imec to capture hydrogen from a process and recycle it. Studies showed such recirculation improved sustainability.

Interestingly, Gallagher noted that improving product yield has a significant sustainability impact. A chip that makes it to testing has a substantial investment in energy and materials. So, if it doesn’t work, everything done to make that chip is wasted. Hence, even as little as a one percent improvement in yield can be beneficial.

Laurent Pain, director of Sustainability and Eco-innovation program at CEA-Leti, also noted material waste during his sustainability presentation on Monday. In addition to etch gas, he pointed to resist, saying that as much as 99 percent of the photoresist dispensed on a wafer during patterning is eventually discarded by chip fabricators. When etching contact holes in a layer, up to 85 percent of the CF₄ is not consumed during processing.

“We have to improve resource use. We have a lot of margin,” Pain said.

To that end, CEA is coordinating the GENESIS project, which is slated to start in May 2025. This three-year program spans 12 countries in Europe and includes 58 partners from chip makers, tool suppliers, research consortiums, material vendors, and material recyclers.

Pain added that cost is one of the main reasons to seek sustainability improvements. Cost, though, can be direct or indirect. The first is the cost of the materials while the second can arise from various sources. There may be expense associated with abatement, in cases where regulation mandates that waste be treated. The expense is more than that associated with capturing or destroying the material. There also will be measurement costs since there will be a need to provide proof of successful elimination of the harmful material.

But regulation can also take other cost driving forms. The EU, for instance, has the Critical Raw Materials Act. It lists 34 critical metals and minerals, many of these found in solar panels, wind turbines, electric vehicles, and energy-efficient lighting. Ensuring critical raw materials are captured for reuse or otherwise conserved can add to expense.

In meeting such requirements, though, Pain pointed out the importance of the big picture. It isn’t enough, for example, to simply look at power reductions and the resulting lowering of greenhouse gas emissions. In an example he cited, for instance, making more wafers means fabrication sites consume more water. So, a narrow focus on power alone might result in an increase in water consumption.

Hence there is a need to do more than look at a single figure of merit when considering sustainability. “You have to take into account all of the factors,” Pain said.

Hank Hogan is a freelance science and technology writer.