Figuring Out Semiconductor Manufacturing’s Climate Footprint

Samuel K. Moore Hi. I’m Samuel K. Moore for IEEE Spectrum‘s Fixing the Future podcast. Before we start, I want to tell you that you can get the latest coverage from some of Spectrum‘s most important beats, including AI, climate change, and robotics, by signing up for one of our free newsletters. Just go to spectrum.ieee.org/newsletters to subscribe. The semiconductor industry is in the midst of a major expansion driven by the seemingly insatiable demands of AI, the addition of more intelligence in transportation, and national security concerns, among many other things. Governments and the industry itself are starting to worry what this expansion might mean for chip-making’s carbon footprint and its sustainability generally. Can we make everything in our world smarter without worsening climate change? I’m here with someone who’s helping figure out the answer. Lizzie Boakes is a life cycle analyst in the Sustainable Semiconductor Technologies and Systems Program at IMEC, the Belgium-based nanotech research organization. Welcome, Lizzie.

Lizzie Boakes: Hello.

Moore: Thanks very much for coming to talk with us.

Boakes: You’re welcome. Pleasure to be here.

Moore: So let’s start with, just how big is the carbon footprint of the semiconductor industry? And is it really big enough for us to worry about?

Boakes: Yeah. So quantifying the carbon footprint of the semiconductor industry is not an easy task at all, and that’s because semiconductors are now embedded in so many industries. So the most obvious industry is the ICT industry, which is estimated to be about approximately 3 percent of the global emissions. However, semiconductors can also be found in so many other industries, and their embedded nature is increasing dramatically. So they’re embedded in automotives, they’re embedded in healthcare applications, as far as aerospace and defense applications too. So their expansion and adoption of semiconductors in all of these different industries just makes it very hard to quantify.

And the global impact of the semiconductor chip manufacturing itself is expected to increase as well because of the fact that we need more and more of these chips. So the global chip market is projected to have a 7 percent compound annual growth rate in the next coming years. And bearing in mind that the manufacturing of the IC chips itself often accounts for the largest share of the life cycle climate impact, especially for consumer electronics, for instance. This increase in demand for so many chips and the demand for the manufacturing of those chips will have a significant impact on the climate impact of the semiconductor industry. So it’s really crucial that we focus on this and we identify the challenges and try to work towards reducing the impact to achieve any of our ambitions at reaching net zero before 2050.

Moore: Okay. So the way you looked at this, it was sort of a— it was cradle-to-gate life cycle. Can you sort of explain what that entails, what that really means?

Boakes: Yeah. So cradle to gate here means that we quantify the climate impacts, not only of the IC manufacturing processes that occur inside the semiconductor fab, but also we quantify the embedded impact of all of the energy and material flows that are entering the fab that are necessary for the fab to operate. So in other words, we try to quantify the climate impact of the value chain upstream to the fab itself, and that’s where the cradle begins. So the extraction of all of the materials that you need, all of the energy sources. For instance, the extraction of coal for electricity production. That’s the cradle. And the gate refers to the point where you stop the analysis, you stop the quantification of the impact. And in our case, that is the end of the processing of the silicon wafer for a specific technology node.

Moore: Okay. So it stops basically when you’ve got the die, but it hasn’t been packaged and put in a computer.

Boakes: Exactly.

Moore: And so why do you feel like you have to look at all the upstream stuff that a chip-maker may not really have any control over, like coal and such like that?

Boakes: So there is a big need to analyze your scope through what is called— in greenhouse gas protocol, you have three different scopes. Your scope one is your direct emissions. Your scope two is the emissions related to the electricity consumption and the production of electricity that you have consumed in your operation. And scope three is basically everything else, and a lot of people start with scope three, all of their upstream materials. And it does have— it’s obviously the largest scope because it’s everything else other than what you’re doing. And I think it’s necessary to coordinate your supply chain so that you make sure you’re doing the most sustainable solution that you can. So if there are— you have power in your purchasing, you have power over how you choose your supply chain. And if you can manipulate it in a way where you have reduced emissions, then that should be done. Often, scope three is the largest proportion of the total impact, A, because it’s one of the biggest groups, but B, because there is a lot of materials and things coming in. So yeah, it’s necessary to have a look up there and see how you can best reduce your emissions. And yeah, you can have power in your influence over what you choose in the end, in terms of what you’re purchasing.

Moore: All right. So in your analysis, what did you see as sort of the biggest contributors to the chip fabs carbon output?

Boakes: So without effective abatement, the processed gases that are released as direct emissions, they would really dominate the total emissions of the IC chip manufacturing. And this is because the processed gases that are often consumed in IC manufacturing, they have a very high GWP value. So if you do not abate them and you do not destroy them in a small abatement system, then their emissions and contribution to global warming are very large. However, you can drastically reduce that emission already by deploying effective abatements on specific process areas, the high-impact process areas. And if you do that, then this distribution shifts.

So then you would see that the direct emission– the contribution of the direct emissions would reduce because you’ve reduced your direct emission output. But then the next-biggest contributor would be the electrical energy. So the scope to the emissions that are related to the production of the electricity that you’re consuming. And as you can imagine, IC manufacturing is very energy-intensive. So there’s a lot of electricity coming in, so it’s necessary then to try to start to decarbonize your electricity provider or reduce your carbon intensity of your electricity that you’re purchasing.

And then once you do that step, you would also see that again the distribution changes, and your scope three, your upstream materials, would then be the largest contributors to the total impact. And the materials that we’ve identified as being the most or the largest contributors to that impact would be, for instance, the silicon wafers themselves, the raw wafers before you start processing, as well as wet chemicals. So these are chemicals that are very specific to the semiconductor industry. There’s a lot of consumption there, and they’re very specific and have a high GWP value.

Moore: Okay. So if we could start with— unpack a few of those. First off, what are some of these chemicals, and are they generally abated well these days? Or is this sort of something that’s still a coming problem?

Boakes: Yeah. So they could be from specific photoresists to— there is a very heavy consumption of basic chemicals for neutralization of wastewater, these types of things. So there’s a combination of having in a high embedded GWP value, which means that it takes a very large amount of– or has a very large impact to produce the chemical itself, or you just have a lot that you’re consuming of it. So it might have a low embedded impact, but you’re just using so much of it that, in the end, it’s the higher contributor anyway. So you have two kind of buckets there. And yeah, it would just be a matter of, you have to multiply through the amounts by your embedded emission to see which ones come on top. But yeah, we see that often, the wastewater treatment uses a lot of these chemicals just for neutralization and treatment of wastewater on site, as well as very specific chemicals for the semiconductor industry such as photoresists and CMP cleans, those types of very specific chemistries which, again, it’s difficult to quantify the embedded impact of because often there’s a proprietary— you don’t exactly know what goes into it, and it’s a lot of difficulty trying to actually characterize those chemicals appropriately. So often we apply a proxy value to those. So this is something that we would really like to improve in the future would be having more communication with our supply chain and really understanding what the real embedded impact of those chemicals would be. This is something that we really would need to work on to really identify the high-impact chemicals and try anything we can to reduce them.

Moore: Okay. And what about those direct greenhouse gas emission chemicals? Are those generally abated, or is that something that’s still being worked on?

Boakes: So there is quite, yeah, a substantial amount of work going into the abatement system. So we have the usual methane combustion of processed gases. There’s also now development in plasma abatement systems. So there are different abatement systems being developed, and their effectiveness is quite high. However, we don’t have such a good oversight at the moment on the amount of abatement that’s being deployed in high-volume manufacturing. This, again, is quite a sensitive topic to discuss from a research perspective when you don’t have insight into the fab itself. So asking particular questions about how much abatement is deployed on certain tools is not such easy data to come across.

So we often go with models. So we apply the IPCC Tier 2c model where, basically, you calculate the direct emissions by how much you’ve used. So it’s a mathematical model based on how much you’ve consumed. There is a model that generates the amounts that would be emitted directly into the atmosphere. So this is the model that we’ve applied. And we see that, yeah, it does correlate sometimes with the top-down reporting that comes from the industry. So yeah, I think there is a lot of way forward where we can start comparing top-down reporting to these bottom-up models that we’ve been generating from a kind of research perspective. So yeah, there’s still a lot of work to do to match those.

Moore: Okay. Are there any particular nasties in terms of what those chemicals are? I don’t think people are familiar with really what comes out of the smokestack of chip fab.

Boakes: So one of the highest GWP gases, for instance, would be the sulfur hexafluoride, so SF6. This has a GWP value of 25,200 kilograms of CO2 equivalent. So that really means that it has over 25,000 times more damaging effects to the climate compared to a CO2, so the equivalent CO2 molecule. So this is extremely high. But there’s also others like NF4 that— these also have over 1,000 times more damaging to the climate than CO2. However, they can be abated. So in these abatement systems, you can destroy them and they’re no longer being released.

There are also efforts going into replacing high GWP gases such as these that I’ve mentioned to use alternatives which have a lower GWP value. However, this is going to take a lot of process development and a lot of effort to go into changing those process flows to adapt to these new alternatives. And this will then be a slow adoption into the high-volume fabs because, as we know, this industry is quite rigid to any changes that you suggest. So yeah, it will be a slow adoption if there are any alternatives. And for the meantime, effective abatement can destroy quite a lot. But it would really be having to employ and really have those abatement systems on those high-impact process areas.

Moore: As Moore’s Law continues, each step or manufacturing node might have a different carbon footprint. What were some of the big trends your research revealed regarding that?

Boakes: So in our model, we’ve assumed a constant fab operation condition, and this means that we’ve assumed the same abatement systems, the same electrical carbon intensities, for all of the different technology nodes, which– yeah. So we see that there is a general increase in total emissions under these assumptions, and we double in total climate impact from N28 to A14. So when we evolve in that technology node, we do see it doubling between N28 and A14. And this can be attributed to the increased process complexity as well as the increased number of steps, in process steps, as well as the different chemistries being used, different materials that are being embedded in the chips. This all contributes to it. So generally, there is an increase because of the process complexities that’s required to really reach those aggressive pitches in the more advanced technology nodes.

Moore: I see. Okay. So as things are progressing, they’re also kind of getting worse in some ways. Is there anything—?

Boakes: Yeah.

Moore: Is this inevitable, or is there—?

Boakes: [laughter] Yeah. If you make things more complicated, it will probably take more energy and more materials to do it. Also, when you make things smaller, you need to change your processes and use– yeah, for instance, with interconnect metals, we’ve really reached the physical limits sometimes because it’s gotten so small that the physical limits of really traditional metals like copper or tungsten has been reached. And now they’re looking for new alternatives like ruthenium, yeah, or platinum. Different types of metals which– again, if it’s a platinum group metal, of course it’s going to have a higher embedded impact. So when we hit those limits, physical limits or limits to the current technology and we need to change it in a way that makes it more complicated, more energy-intensive— again, the move to EUV. EUV is an extremely energy-intensive tool compared to DUV.

But an interesting point there on the EUV topic would be that it’s really important to keep this holistic view because even though moving from a DUV tool to an EUV tool, it has a large jump in energy intensity per kilowatt hour. The power intensity of the tool is much higher. However, you’re able to reduce the number of total steps to achieve a certain deposition or edge. So you’re able to overall reduce your emissions, or you’re able to reduce your energy intensity of the process flow. So even though we make all these changes and we might think, “Oh, that’s a very powerful tool,” it could go and cut down on process steps in the holistic view. So it’s always good to keep a kind of life cycle perspective to be able to see, “Okay, if I implement this tool, it does have a higher power intensity, but I can reduce half of the number of steps to achieve the same result. So it’s overall better. So it’s always good to keep that kind of holistic view when we’re doing any type of sustainability assessment.

Moore: Oh, that’s interesting. That’s interesting. So you also looked at— as sort of the nodes get more advanced and processes get more complex. What did that do to water consumption?

Boakes: Also, so again, the number of steps in a similar sense. If you’re increasing your number of process steps, there would be an increase in the number of those wet clean steps as well that are often the high-water-consumption steps. So if you have an increased number of those particular process steps, then you’re going to have a higher water consumption in the end. So it is just based on the number of steps and the complexity of the process as we advance into the more advanced technology nodes.

Moore: Okay. So it sounds like complexity is kind of king in this field.

Boakes: Yeah.

Moore: What should the industry be focusing on most to achieve its carbon goals going forward?

Boakes: Yeah. So I think to start off, you need to think of the largest contributors and prioritize those. So of course, if you’re looking at the total impact and we’re looking at a system that doesn’t have effective abatement, then of course, direct emissions would be the first thing that you want to try to focus on and reducing, as they would be the largest contributors. However, once you start moving into a system which already has effective abatement, then your next objective would be to decarbonize your electricity production, go for a lower-carbon-intensity electricity provider, so you’re moving more towards green energy.

And at the same time, you would also want to try to target your high-impact value chain. So your materials and energy that are coming into the fab, you need to look at the ones that are the most highly impacting and then try to find a way to find a provider that does a kind of decarbonized version of the same material or try to design a way where you don’t need that certain material. So not necessarily that it has to be done in a sequential order. Of course, you can do it all in parallel. It would be better. So it doesn’t have to be one, two, three, but the idea and the prioritizing comes from targeting the largest contributors. And that would be direct emissions, decarbonizing your electricity production, and then looking at your supply chain and looking into those high-impact materials.

Moore: Okay. And as a researcher, I’m sure there’s data you would love to have that you probably don’t have. What could industry do better about providing that kind of data to make these models work?

Boakes: So for a lot of our a lot of our scope three, so that upstream, that cradle-to-fab, let’s call it— those impacts. We’ve had to use quite a lot— we had to rely quite a lot on life cycle assessment literature or life cycle assessment databases, which are available through purchasing, or sometimes if you’re lucky, you have a free database. So I would say– and that’s also because my role in my research group is more looking at that LCA and upstream materials and quantifying the environmental impact of that. So from my perspective, I really think that this industry needs to work on providing data through the supply chain, which is standardized in a way that people can understand, which is product-specific so that we can really allocate embedded impact to a specific product and multiply that through then by our inventory, which we have data on. So for me, it’s really having a standardized way of communicating sustainability impact of production, upstream production, throughout the supply chain. Not only tier one, but all the way up to the cradle, the beginning of the value chain. So this is something– and I know it is evolving and it will be slow, and it does need a lot of cooperation. But I do think that that would be very, very useful for really making our work more realistic, more representative. And then people can rely on it better when they start using our data in their product carbon footprints, for instance.

Moore: Okay. And speaking of sort of your work, can you tell me what imec.netzero is and how that works?

Boakes: Yeah. This is a web app that’s been developed in our program, so the SSTS program at IMEC. And this web app is a way for people to interact with the model that we’ve been building, the LCA model. So it’s based on life cycle assessment, and it’s really what we’ve been talking about with this cradle-to-gate model of the IC-chip-manufacturing process. It tries to model a generic fab. So we don’t necessarily point to any specific fab or process flow from a certain company. But we try to make a very generic industry average that people can use to estimate and get a more realistic view on the modern IC chip. Because we noticed that, in literature and what’s available in LCA databases, the semiconductor data is extremely old, and we know that this industry moves very quickly. So there is a huge gap between what’s happening now and what is going into your phones and what’s going into the computers and the LCA data that’s available to try to quantify that from a sustainability perspective. So imec.netzero, we work with all of— we have the benefit of being connected with the industry and now a position in IMEC, and we have a view on those more advanced technology nodes.

So not only do we have models for the nodes that are being generated and produced today, but we also predict the future nodes. And we have models to predict what will happen in 5 years’ time, in 10 years’ time. So it’s a really powerful tool, and it’s available publicly. We have a public version, which is a limited– it has limited functionality in comparison to the program partner version. So we work with our program partners who have access to a much more complicated and, yeah, deep way of using the web app, as well as the other work that we do in our program. And our program partners also contribute data to the model, and we’re constantly evolving the model to improve always. So that’s a bit of an overview.

Moore: Cool. Cool. Thank you very much, Lizzie. I have been speaking to Lizzie Boakes, a life cycle analyst in the Sustainable Semiconductor Technologies and Systems Program at IMEC, the Belgium-based nanotech research organization. Thank you again, Lizzie. This has been fantastic.

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