# How Chipmakers Are Taming Electromigration at Three Nanometers

An episode of [The Hardware Podcast with Fexingo: Chips, Devices, and Electronics Engineering Conversations](https://invisiblenetwork.ai/podcast/1896799982), 21 Jun 2026, 13 min.

Audio: https://audio.fexingo.com/business/the-hardware-podcast/episode-0065.mp3

In this episode of The Hardware Podcast, Lucas and Luna explore how advanced chip designers are tackling electromigration — the slow migration of metal atoms that can cause chip failure — at the three-nanometer node. They dive into the physics behind copper interconnects, why cobalt and ruthenium are replacing copper in critical layers, and how TSMC and Intel are using barrier engineering and novel liner materials to extend chip lifespan. Specific data includes the 10x improvement in electromigration resistance achieved with cobalt liners at 2nm dimensions. The discussion also touches on the hidden role of grain boundaries and the trade-off between performance and reliability. A must-listen for anyone curious about the unsung materials science behind modern processors. #Electromigration #Semiconductors #ChipDesign #3Nanometer #TSMC #Intel #CopperInterconnects #Cobalt #Ruthenium #MaterialsScience #Reliability #Technology #Hardware #Engineering #FexingoBusiness #BusinessPodcast #TheHardwarePodcast #Podcast Keep every episode free: buymeacoffee.com/fexingo

## Transcript

Lucas: You know how sometimes a chip just dies after a few years — not because it got fried, not because you dropped it, but because the metal wires inside it literally moved?
Luna: Moved? Like the atoms just packed up and left?
Lucas: Pretty much. It's called electromigration, and it's been a headache for chip designers since the 1960s. But at today's three-nanometer node — where wires are barely a few dozen atoms wide — it's become the single biggest reliability challenge.
Luna: I remember hearing about this in my materials science class. It's when electrons slam into metal atoms and literally push them downstream, like wind pushing sand.
Lucas: Exactly. And over time, those atoms pile up at one end, forming a hillock that can short-circuit, while the other end thins out and eventually breaks — an open circuit. In a chip with billions of interconnects, even a tiny failure rate becomes a big problem.
Luna: So how bad is it at three nanometers? Are we talking about chips dying after a year?
Lucas: No, the foundries have gotten good at managing it, but the physics gets worse as you shrink. Copper's electromigration resistance scales poorly at line widths below ten nanometers. At three nanometers, the grain structure of copper becomes highly irregular, and grain boundaries become highways for atomic migration.
Luna: So what's the fix? Switch to a different metal?
Lucas: That's exactly what's happening. Cobalt and ruthenium are becoming the go-to materials for the most critical layers. Cobalt has a higher melting point and better electromigration resistance — roughly ten times better than copper at these dimensions. But it's more resistive, so you can't use it everywhere.
Luna: So it's a trade-off — better reliability but worse performance?
Lucas: Right. That's why you see a hybrid approach. TSMC, for instance, uses cobalt in the lowest metal layers — M1 and M2 — where currents are highest and wires are thinnest. Then they switch back to copper for the upper, thicker layers where electromigration is less of a concern. Intel's doing something similar with ruthenium in some of their interconnects.
Luna: Interesting. So the chip becomes a kind of metallurgical sandwich.
Lucas: Exactly. And it's not just the metal itself; the barrier layers matter too. Traditionally, you put a thin layer of tantalum or tantalum nitride around the copper to prevent it from diffusing into the surrounding silicon dioxide. But as wires get narrower, the barrier takes up a bigger fraction of the cross-section, leaving less room for the actual conductor.
Luna: So you need a barrier that's just a few atoms thick — or none at all.
Lucas: That's the holy grail: a barrierless interconnect. Cobalt and ruthenium are interesting because they don't need a barrier — they naturally don't diffuse into the dielectric. That means you can have a pure metal wire with maximum cross-section for conduction.
Luna: But you said cobalt is more resistive. Does that negate the benefit?
Lucas: It depends on the line width. At very narrow dimensions — say, below seven nanometers — the resistivity of copper skyrockets due to surface scattering and grain boundary effects. Cobalt's resistivity, while higher in bulk, scales better at small dimensions because its electron mean free path is shorter. So at three nanometers, cobalt can actually have lower effective resistivity than copper.
Luna: That's counterintuitive. So the material that's worse in bulk becomes better at the nanoscale.
Lucas: Exactly. And that's why you're seeing a lot of research into ruthenium as well. It has even better electromigration resistance than cobalt, and its resistivity scaling is also favorable. The challenge is that ruthenium is harder to etch and deposit uniformly.
Luna: So every new node brings a materials science problem as much as a lithography problem.
Lucas: Completely. And electromigration is just one of several reliability issues. There's also stress migration, which is driven by mechanical stress rather than electron wind, and time-dependent dielectric breakdown, where the insulating layers degrade over time. But electromigration is the one that gets the most attention because it's so directly tied to current density, and current density keeps going up as chips get more powerful.
Luna: I've seen some papers on using graphene as an interconnect material. Would that solve the problem?
Lucas: Graphene has incredible current-carrying capacity — it can handle current densities a thousand times higher than copper before failing. But the practical challenges are enormous. You need perfect, single-layer graphene with no defects, and you need to integrate it with standard CMOS processing. That's still a long way off.
Luna: So for the next few nodes, it's cobalt, ruthenium, and better barrier engineering.
Lucas: That's the near-term picture. And it's worth noting that foundries have been quietly deploying these materials for a few years now. TSMC's N3 process, which went into high-volume manufacturing in late 2023, uses cobalt in the first two metal layers. Intel's Intel 3 and Intel 18A processes use a combination of cobalt and copper with advanced barriers.
Luna: So the consumer doesn't see it, but it's a huge part of why modern chips can run at high clock speeds without dying prematurely.
Lucas: Right. And reliability requirements are getting stricter, especially for automotive and data center chips that need to last ten years or more. The automotive standard AEC-Q100 requires chips to pass electromigration tests at elevated temperatures, typically 125 degrees Celsius, for thousands of hours. That's a brutal test.
Luna: That reminds me — I read that some early three-nanometer chips from a certain manufacturer had early failure issues. Was that electromigration?
Lucas: There were rumors, but nothing confirmed publicly. Most likely, if there were issues, they were related to process integration — the combination of new materials and new geometries. Electromigration is a wear-out mechanism; it takes time to manifest, so early failures are usually due to defects, not electromigration itself.
Luna: So how do chip designers actually test for electromigration? I imagine you can't just run a chip for ten years and see if it fails.
Lucas: They use accelerated testing. They run test structures — simple lines of metal — at elevated temperatures and current densities, and then extrapolate using Black's equation. That's an empirical model that relates mean time to failure to current density and temperature. It's been around since the 1960s, but it's still the industry standard.
Luna: And the foundries share that data with chip designers so they can set design rules — like maximum current per wire width.
Lucas: Exactly. Every foundry provides a set of electromigration rules: for a given metal layer and line width, there's a maximum current density you're allowed to design to. If you violate it, the chip might still work in testing but fail in the field after a year or two.
Luna: So it's part of the EDA flow — the place and route tools check electromigration automatically.
Lucas: Right. Modern electronic design automation tools have built-in electromigration analysis. They simulate current flow across the entire chip and flag any wire that exceeds the reliability limits. Then designers can widen the wire or add more vias to spread the current.
Luna: But widening a wire costs area, and area is money.
Lucas: It's a constant trade-off. That's why you see things like via redundancy — putting two or three vias in parallel instead of one, so if one fails, the others can carry the load. Or using slot-shaped vias instead of square ones to reduce current crowding.
Luna: Current crowding — that's another electromigration effect, right? Where current bunches up at the corners of a via.
Lucas: Exactly. At the interface between a via and a metal line, the current density can be ten times higher than the average. That's where voids tend to form first. So designers use tapered vias or multiple vias to spread the current more evenly.
Luna: This is the kind of detail that never makes it into the marketing slides about a new chip.
Lucas: Never. But it's the difference between a chip that works reliably for five years and one that dies in eighteen months. And as we push toward two nanometers and beyond, these issues will only get more acute.
Luna: Speaking of which — have you seen any research on machine learning to predict electromigration hotspots?
Lucas: Yes, there's been interesting work from groups at UC Berkeley and IMEC. They train neural networks on simulation data to predict where electromigration failures are likely to occur, which can speed up the design rule development process. But it's still supplementary to traditional physics-based simulation.
Luna: It feels like every new node is a battle against physics, and the weapons are better materials and smarter design tools.
Lucas: That's the semiconductor industry in a nutshell. And electromigration is one of the oldest enemies. It was first observed in the 1960s on early integrated circuits, and we've been fighting it ever since. But the solutions keep getting more creative.
Luna: So what's next? Beyond ruthenium and cobalt, are there other candidates?
Lucas: There's molybdenum, which has similar properties to ruthenium but is cheaper and easier to deposit. And there's work on intermetallic compounds — like copper-aluminum alloys — that have better electromigration resistance than pure copper. But those come with their own integration challenges.
Luna: It's amazing how much engineering goes into something as invisible as a metal wire.
Lucas: If today's conversation gave you something usable — a new way to think about chip reliability, or a detail you can bring up the next time someone asks why chips don't just keep shrinking — consider supporting the show. We keep this podcast ad-free thanks to listeners who chip in at buy me a coffee dot com slash fexingo. No pressure, but if the content is valuable to you, that's the easiest way to keep it coming.
Luna: Yeah, it really makes a difference. And we appreciate everyone who's already supported us.
Lucas: So back to electromigration — one more thing that's changing is the role of grain boundaries. In narrow lines, the grain structure becomes bamboo-like, with grains spanning the entire width. That actually helps because there are fewer grain boundaries for atoms to migrate along. But the orientation of the grains matters too. Copper with a <111> texture — where the crystal lattice is oriented a certain way — has much better electromigration resistance than random texture.
Luna: So you can engineer the crystal structure during deposition?
Lucas: To some extent. By controlling the seed layer and the plating conditions, you can promote a preferred grain orientation. TSMC and Intel have both published on optimizing copper texture for electromigration. It's another lever they can pull.
Luna: So it's not just what metal you use, but how you deposit it, and what crystal orientation it has.
Lucas: Exactly. And with atomic layer deposition, you can control film thickness to within a single atomic layer. That level of control is essential when the entire wire is only twenty atoms wide.
Luna: Twenty atoms wide. That's mind-boggling.
Lucas: And yet we're making billions of them, and they mostly work. I think that's the most remarkable thing about modern chips — not just the performance, but the reliability, given the scale.
Luna: Well, thanks for making electromigration interesting. I'll never look at a chip the same way again.
Lucas: Glad to hear it. Next time, we'll talk about something completely different — or maybe we'll dive deeper into another reliability mechanism.
Luna: I'd love that. Until next time.

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