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Comment by alted | Hacker News Reader

Judging from [1], Sam Zeloof's plan might include using electron beam lithography, which scans an electron beam over a wafer surface, instead of normal photolithography. This can get high resolution (10nm) comparable with EUV, and could theoretically be built out of a hacked scanning electron microscope. Photolithography is the step that limits fabrication size, so e-beam litho allows cheap transistors comparable with state-of-the-art.

The main problem is e-beam litho is extremely slow. It might take ~1 day to do a single photolithography step for a 1x1cm chip, whereas an EUV machine can pattern a 300mm diameter silicon wafer in < 1 minute. (The next problem is making everything reliable. Billions of transistors (a modern CPU) needs a failure rate per transistor of better than 1e-9.)

Maybe that's enough for extremely-low-volume production?

[1] https://mobile.twitter.com/szeloof/status/154993704406717235...

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Mapper[1] did this, tried to commercialize it and went bankrupt in 2018 and ASML scooped up the remains[2].

[1] https://nl.wikipedia.org/wiki/Mapper_Lithography (no English page available)

[2] https://www.asml.com/en/news/press-releases/2019/asml-agrees...

Doesn’t necessarily make it a bad idea to try again. It seems that photolithography as a process is stretched to its limits. Easy to see the diminishing returns. The electron beam lithography is a different kind of process. It seems like it’s precise enough, just slow. That sounds like good news to me. “Make it go faster” is something we typically can achieve.

> ... electron beam lithography ... could theoretically be built out of a hacked scanning electron microscope

Not only theoretically. Sam hacked his own scanning electron microscope and did electron beam lithography in 2018.

http://sam.zeloof.xyz/e-beam-lithography/

e-beam litho is anything but fast though: the machines are cheaper but they are much much slower in wafer throughput than the insanely expensive ASML EUV machines.

Now the website claims a fast fab, but leaves it open what that means: fast production of wafers? Or slow production of wafers that run fast?

e-beam litho just seems strange to me since electron beam 3D printing is just as fast as using lasers, so clearly the scanning part isn't the bottleneck. What is the bottleneck in this case?

> since electron beam 3D printing is just as fast as using lasers

Interesting. What sort of resolution is that 3D printing though?

> What is the bottleneck in this case?

My guess would be using a single beam? Perhaps it's possible to scale this up to multiple beams working on a die or wafer at a time time?

Which brings up another interesting question. Would this process require the same kind of wafer/substrate as traditional EUV machines? Perhaps using this approach opens up the possibility of using different materials that are easier, cheaper and faster to produce?

Dont't traditional kinds of wafers have to be grown and sliced from exotic/rare materials? If so the additional time to "etch" with this new process might be offset by other factors such as what goes in to preparing the wafer?

> Interesting. What sort of resolution is that 3D printing though?

Around 50 microns I believe. Not at lithography resolutions obviously, but that's limited by metal powder grain size.

> My guess would be using a single beam?

Electron beams can scan a whole print bed very quickly to heat up the whole top layer [1] which can't be done using lasers. This can be done easily with electrons since they are deflected using magnetic coils, like good old CRT monitors, but this can't be done using lasers because they have to move the mirrors mechanically.

That's why it seemed weird that photolithography would be so much faster, but maybe it's as you say, lasers can be stacked for parallelism to make up for those downsides. Stacked electron beams might interfere with each other because you can't really isolate magnetic fields.

[1] https://www.youtube.com/watch?v=jqjD-FWMexo

Photolithography fabs don’t use scanning lasers — they shine light through a mask and expose a large area at once.

Crazy they have physical masks with features as small as 7nm. I assume those are movable somehow but that seems like incredibly delicate work.

You can use lenses and curved mirrors to make a larger mask focus the light onto a smaller area.

That still seems pretty delicate. The lenses and mirrors would have to be aberration-free to an extreme degree so as to not introduce too many artifacts, and moving the mask further from the surface would increase risk of diffraction artifacts, no?

It is, but that's how modern semiconductor lithography is done. Massive lenses and mirrors (both made of different materials that normal, since they need to have optical properties at wavelengths much smaller than human vision) are manufactured at great cost to ensure that it is free of aberrations. The extremely limited supply of these is actually one of the many factors that restricts the ability to move to newer processes and scale production capability of newer lithographies.

For good telescope optics, we look for something like 1/4 - 1/6 wavelength tolerance, minimum. That's for optical wavelengths, but photolithography is in the UV range, so that's already stricter tolerance in absolute terms because of the shorter wavelength, but how does the tolerance in relative terms compare? Thanks for the info!

Read up on the Zeiss optics that go into the ASML EUV machines. (or at least what is publicly available knowledge). It's truly insane

They go pretty hardcore on the optics. Have a look at their light path:

https://www.asml.com/-/media/asml/images/technology/43679-in...

One youtube video[1] I watched had someone state that if you scaled up one of the curved mirrors to the size of the Earth, the largest imperfection would be the width of a hair.

[1] https://www.youtube.com/watch?v=en7hhFJBrAI around 7:30

> Crazy they have physical masks with features as small as 7nm.

Everything about this is crazy complex, and the state of the art in any given year is also secret to TSMC and other tiny-feature-size fabs.

But in addition to gradually upping the narrow-bandwidth/phase-coherent illumination frequency every year (which has many problems but continues to see continual progress), they've also long been using techniques to work around the diffraction limit/resolution barrier [1], such as subwavelength metamaterial "hyperlenses" / "superlenses" (previously widely thought to be impossible even in theory) [2][3] and "assist features" and other non-traditional masking elements to pre-compensate for imaging distortions [4]. Plus they fiddle a lot with the chip process to tune it in weird ways to assist with or compensate for the previous issues.

[1] https://en.wikipedia.org/wiki/Diffraction-limited_system

[2] https://en.wikipedia.org/wiki/Superlens#Theory

[3] "Subwavelength-Grating Metamaterial Structures for Silicon Photonic Devices" https://ieeexplore.ieee.org/document/8424820

[4] https://en.wikipedia.org/wiki/Extreme_ultraviolet_lithograph...

> That's why it seemed weird that photolithography would be so much faster, but maybe it's as you say, lasers can be stacked for parallelism to make up for those downsides.

The reality of how this is done is so much more complex than I would have thought: https://www.youtube.com/watch?v=f0gMdGrVteI Traditional techniques such as masks don't work when dealing with xrays.

EUV can expose a whole chip image in a single shot. Raster scanning electrons takes about 4 hours to do the same image.

You need to deposit a specific amount of energy into your resin to polymerize it, that takes time as you can't just crank up the amount of charge or the energy / electron in your e-beam as that will usually increase the energy variance and thereby the aberration. It's much easier to produce a coherent beam of light with sufficient energy than a coherent beam of electrons with comparable energy.

No the scanning is the bottleneck, scanning laser photolithography is equally slow. For mass production of chips, photolithography is done with a light source that illuminates a "large" area all at once.

If the machines could be super cheap you could make up for slow by having many run in parallel (~~not parallel beams working on same chip, since electrons deflect each other, but machines running in parallel~~).

Edit: linked below, https://www.ims.co.at/en/products/ , says it uses 512x512 beams with a beam field of only 82um. Is that spacing between beams, or width of all the beams together?

Back-of-the-envelope, a beam array of 256k beams could plausibly level that 1 minute vs 1 day ratio.

The machines themselves couldn't be "super" cheap, that's impossible. You still have to deposit the e-beam resist while keeping the wafers extremely clean. This is non-trivial.

The only route to economic viability is absolutely massive beam parallelism inside the tool. But at that scale, there's serious questions about accuracy/reliability. Just one out of hundreds of thousands (or millions) of beams fails for a microsecond and the chip is ruined. This is a problem that is effectively sidestepped for traditional litho -- the masks themselves are created by (slow) e-beam, but mask inspection tools ensure that the masks are perfect before they are actually used to process product wafers.

> The machines themselves couldn't be "super" cheap, that's impossible.

There are a few dimensions of cost that can be optimized though, right? My understanding is that ASML is making ~10s of these EUV machines per year because of the extreme complexity of many components.

Sure. Chief among those dimensions is the fact that it's not used as a serious production technology, so the manufacturing of these systems doesn't benefit from economy of scale.

E-beam certainly does provide a bounding limit on how expensive EUV can get, but we're not in danger of hitting that limit anytime soon.

I expect that EUV will become cheaper/more productive per dollar in the medium term, unless ASML starts acting uncomfortably monopolistically (and it's probably in their interest to drive EUV adoption to starve out Nikon and Canon, anyway)

Maybe the error rate of massively parralel e-beam could be good enough for ML chips?

I don't think being an ML chip means the defects are necessarily less fatal. These often interfere with the actual functioning of the chip, cause shorts, etc -- it's not just a matter of the TTL being very slightly messed up somewhere.

You could imagine chips that are engineered for redundancy / defect resistance, but that would make them a lot less performant so it's highly questionable whether that can be justified by any cost savings on litho.

> You still have to deposit the e-beam resist while keeping the wafers extremely clean. This is non-trivial.

True, but this is more or less the same process for e-beam and photolithography (as I understand it). I don’t see a fundamental reason why one couldn’t replace one ASML EUV machine with, say, 1000 e-beam machines and run them all in parallel. You would need the e-beam machines to be extremely reliable, but they’re conceptually simple devices and this should be possible.

(With vague ballpark numbers from the Internet, an EUV machine appears to be about 10k times as expensive as a SEM. Building 10k e-beam machines at the same cost as one Alibaba SEM would be an interesting challenge, and there would be factors pushing the price in both directions.)

> I don’t see a fundamental reason why one couldn’t replace one ASML EUV machine with, say, 1000 e-beam machines and run them all in parallel.

Fab floorspace is also very expensive, nevermind that's not even close to a realistic price per system (the factory interface alone costs $100k+)

Could also do multiple parallel e-beams to a chip (within reason). This might amortize some of the cost.

Definitely, but it doesn't solve the reliability problem

I presume meaning "fast turnaround on producing a design", i.e. less time needed to setup tooling.

Like the concept of Fast Fashion

My short introduction into the fab industry exactly echos this. Allowing US companies to turnaround prototypes quickly is a valuable business. Perhaps they aim to get a foothold with this and slowly ramp up to high volume manufacturing.

There are some theoretical approaches that you could use to make e-beam a lot faster, and I'm not sure anyone has really explored them due to the unreasonable effectiveness of photolithography. Basically, SEMs and e-beam machines today use a low- or medium-power electron beam that they treat as a static beam, and scan slowly to keep the "static" assumption. If you instead think if it as a traveling particle stream, you may be able to "pipeline" the process of steering the beam as it travels down the microscope, allowing you to crank up the power and run the process a lot more quickly. It would be very cool to see a startup pursue super-fast e-beam and make it work, and it's a niche I'm excited to see explored.

A common approach is to use multiple electron beams in parallel ([1] is up to 262144 beams!). This is starting to be used commercially to create the masks for photolithography.

[1] https://www.ims.co.at/en/products/

Interesting. So I wonder what it is that Atomic Semi is attempting to do that is novel/different/unique?

AFAIK, the best performance IMS were able to achieve with the 512x512x50nm e-beams was 1cm^2 per hour. That's acceptable for etching masks, but still not feasible for chip manufacturing, as wafer goes through 40-50 exposures each would be taking days to complete.

Personally, I think there is an undertapped market for extremely low volume productions. The cost of a mask set is in the hundreds of thousands of dollars, and there is very little custom or domain-specific IC design.

I do think it's a slow market to emerge. They'd need very patient funding. If nothing else, tooling needs to catch up, which is 5+ years.

apart from massively-parallel beam systems as discussed elsewhere here, it seems more likely to me that e-beams could be used for mask-making, which might make it easier for smaller clients to make the jump to modern processes.

like if you can do a 7nm or 14nm tier mask maybe that becomes a pivot to a 28nm actual production process, or maybe it makes multipatterning and some of the other advanced-node tricks more accessible at a semi-reasonable cost.

I wonder if e-beam lithography would make registration easier. With photolithography, I assume one must position the wafer relative to the mask extremely precisely. With e-beam lithography, the tool is a scanning electron microscope, and as long as the wafer doesn’t move, the software could potentially locate it to essentially arbitrarily high precision and then offset and rotate the scanning pattern accordingly.

ASML surely charges plenty for their alignment hardware:

https://www.asml.com/en/news/stories/2021/fellow-simon-mathi...

From the description of a “fast fab” and this, perhaps the play is to beat photolithogaphic fans on turnaround, e.g. GDS-to-first-silicon latency. An e-beam doesn’t need masks made.

I was under the impression that electron beam could fundamentally get much smaller than light (electrons are “smaller” than photons in some funky physics sense), but was just really slow.

Also (fuzzy memories of semiconductor classes, but) the size doesn’t tell the whole story, right? With photons I’m under the impression that the wavelength of the light is much higher than the feature size, so they have to do funky things with the masks to make it all work out. Playing with interference or whatever. (Someone who knows more about this can feel free to embarrass me, I’m sure it will be educational!)

Electrons are relatively speaking more like the nice little billiards ball thwacking away at the SI that we like to imagine.

> Electrons are relatively speaking more like the nice little billiards ball thwacking away at the SI that we like to imagine.

They are as long as you keep a close eye on them…

And I’m sure charged billiards balls present plenty of fun challenges.

> The main problem is e-beam litho is extremely slow.

There are now some multi-beam systems.[1]

[1] https://multibeamcorp.com/products/

1 day for (1cm)^2 is 15 minutes for (1mm)^2. That might be okay for a start -- I suppose they do not want to go for the largest chips right from the beginning.

At the N5 node 1mm^2 of a fully finished wafer is worth about 25 cents. This may have undergone hundreds of steps. If we assume the chips we're making can be done in 100 steps, one of these E-Beam Lithography machines costs the same amount as a scanning electron microscope, can run 24/7 for years, and there are zero costs to operate, and we need to break even in 2 years, then we need to charge about 450 times as much as a mass produced chip. Obviously under more realistic conditions, that multiplier would have to be way higher.

While for steady state production, a chip could be produced every couple of hours, no one is going to pay tens of thousands per chip for even a limited production run. If you are doing a one off prototype that justifies an extremely high pricetag, you have long lead times waiting for the chip to go through the various steps.

Honestly you'd be better off just making custom masks.

E-beam is mentioned in their hiring verbiage:

> We believe our team and lab can build anything. We’ve set up 3D printers, a wide array of microscopes, e-beam writers, general fabrication equipment - and whatever is missing, we’ll just invent along the way.

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