Can lithography help save the planet?

The topic for an evening panel discussion at the 2023 Advanced Lithography + Patterning conference was saving the planet. Specifically, the group discussed improving the sustainability of semiconductor manufacturing via lithography and related areas. It turns out, though, that lithography’s role in sustainability is a complicated one. Also, being environmentally friendly can help the bottom line in not-so-obvious ways.

Emily Gallagher, a principal member of the technical staff at imec, noted that sustainability has momentum, due to government regulations, shareholder pressure, and customer demands. "Most big companies have been making net zero pledges. So it's going to have a big impact on all of us.”

Akihisa Sekiguchi, a corporate fellow at Tokyo Electron, noted that this impact will be widespread because a net zero pledge can encompass Scope 1, 2, and 3 emissions. Scope 1 emissions are those a company directly makes, such as by heating a building using fossil fuel instead of renewable energy. Scope 2 covers indirect emissions, like the emissions a utility makes in generating electricity used to run a manufacturing facility. Scope 3 covers those emissions created up and down the supply chain, an example being the greenhouse gases produced by a tool making semiconductor chips in a wafer fab. Such emissions would be Scope 3 for the tool maker.

It's this last bucket that will have the largest impact. “About 97 percent of our emission relates to what our products release,” Sekiguchi said. Thus, in reaching its own 2050 net zero Scope 3 pledge, the company has to think about the tools they sell and how they’re used.

Improving sustainability to meet goals can take many forms. Panelist John Cahill of ASML-Cymer, noted that his company’s tools use aluminum, and that every ton of the metal produced releases the equivalent of 16 tons of CO₂ into the air if the energy comes from a standard mix of fuels. By changing the design of the tools, the company saved aluminum and improved sustainability.

“We’ve been able to offset 15 million pounds of CO₂,” Cahill said. Reducing the need for aluminum has also meant that supply shortages have had less of an impact on the ability to get tools out the door.

Mark Merrill, vice president of corporate development at Lam Research, said the company is taking a multifaceted approach. For instance, the goal is to use 100 percent renewable energy by 2030, which will cut emissions. Additionally, through a redesign, the company pulled 15,000 pounds of aluminum out of a platform by shrinking it. Specific to lithography, Lam introduced a dry resist that is deposited, using as much as 10 times less material than alternatives and increasing the efficiency of EUV steppers.

“We take ESG seriously,” Merrill said, using the acronym for the environmental, social, and governance aspects of corporate management.

Speaking of EUV steppers, Ryan Russell, corporate vice president at Intel, noted that moving from multipattern DUV to single pass EUV allowed the company to drop hundreds of steps from its processing flow. So, even though an EUV stepper was perhaps 10 times or more energy intensive than a DUV alternative, the net effect was a significant drop in overall emissions.

Similar unexpected interactions exist elsewhere. For instance, Russell said that a more expensive tool that emits less may be cheaper when everything is considered. Carbon tetrafluoride, CF4, is difficult to abate and is usually burned up by using natural gas. This is only one of many process gases whose emission is regulated. A single wafer fab may have 2,000 point-of-use abatement systems of various types, Russell noted.

Those systems produce greenhouse gas emissions and they cost money to buy and operate. Additionally, they must be mounted atop the building, leading to extra structural costs and more emissions. So, if some of the money that would have gone into abatement is instead spent on buying a cleaner but more costly tool, then both Intel and the equipment supplier may come out ahead.

As for sustainability in general, Russell noted it’s been a focus of Intel from the beginning. He began his career at the company living in an apartment just minutes from a wafer fab, giving him a personal reason to care about what was going into the air.    

“I was breathing what was emitted,” he recalled.

Looking toward the future, Chris Jones, environmental solutions business development manager at Edwards Vacuum, pointed to efforts to improve recycling by capturing critical gases and reusing them. EUV processes use a lot of hydrogen, much of which is produced from hydrocarbon fossil fuels as a feedstock. Thus, there can be a double hit, if the energy to create the hydrogen comes from other fossil fuels.

“We’ve been developing hydrogen recycling systems,” Jones said. The goal is reach at least an 80 percent recycle rate.

Asked about what’s needed, the panelists pointed to a few areas. One is standards and models. Today, there is no accepted method to determine carbon footprint, with some companies operating similar businesses saying their Scope 3 burden is only 10 percent of the total while other companies put it at higher than 50 percent.

There also is a need for better measurement capabilities. Some rules and regulations contemplated for allowable levels of chemicals in water call for such low levels as to require orders of magnitude improvement in measurement performance.

A third requirement is for better tools to deal with emissions. Being able to get rid of CF₄ cost competitively using a plasma, for example, would be useful because a plasma can be generated using renewable energy, something not possible when the abatement method involves burning the emission via a fossil fuel. The panel even suggested such technology, if developed, would be shared, as that would drive volumes for the abatement technology up and costs down.  

A final recommendation is that solutions – models, tools and standards – must be like the environment itself. Solutions cannot be done in a piecemeal fashion, with each company and country going its own way.

“It has to be global,” Sekiguchi said.