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Comment by geenew | Hacker News Reader

Any idea why the colour on the fab floor is an odd yellow hue? Is the standard colour spectrum for interior lighting not compatible with chipmaking? I'm imagining a situation akin to the darkroom requirements for processing photographs.

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Anything UV sensitive is usually done in a yellow room, so that's probably it.

I know this is exactly the case for PCB manufacture and printing press plate making to lessen accidental exposure, so it's exactly like a red safelight in a darkroom.

My understanding is that was the original purpose, but probably unnecessary given that all the relevant process steps are encased in tools that are not exposed to the general clean room environment in operation (they have to maintain a higher grade of clean room internally).

However, I suspect it's probably going to continue being propagated forward due to Copy Exactly which has historically meant that Intel documents and copies the smallest details in all their fabs just in case they are necessary. In the end, if it ain't broke...

In short, they've cargo culted themselves. No wonder they've lost their place as makers of powerful processors.

Why would you not want the additional protection if you have to pick a colour to make the room anyways?

Copying everything implies they do not have full understanding of what makes for a successful process.

It's possible that some level of unresolved empirical "magic" be involved in the process, which does not diminish the value of the end product. Why deprive yourself of hard learned lessons even if you don't understand it all?

Chesterton's Fence [0] should overrule fear of cargo culting, especially when the fence (or in this case color) was clearly put up by people who really knew what they were doing at the time.

Unless there is a significant cost to it, and unless the benefit is understood, there is no reason that they should be faulted as ignorant cargo cultists simply for keeping it in place.

[0] https://www.chesterton.org/taking-a-fence-down/

Right. There's not a compelling reason to switch and there's more than a hint of CYA mixed in with Chesterton's Fence:

https://www.bloomberg.com/news/articles/2016-06-09/how-intel...

> For decades, Intel’s cleanrooms have been lit like darkrooms, bathed in a deep, low yellow. “That’s an anachronism,” says Mark Bohr, a small, serious man who has spent his entire 38-year career making chips, and who’s now Intel’s top manufacturing scientist. “Nobody’s had the courage to change it.”

This remembers me, when many years ago I worked with old chemical photography - used special light to limit parasitic exposure of film and photopaper.

Usually used dark red light, or yellow-green.

And I lived in absolutely typical apartment, and used for photography ordinary bathroom, but switched off normal lights and used special lights, and apartments become looking like them from fantastic films.

So, yes, my first education electronics and I've few times been at real fabs. At fabs there are two things which don't appear in typical homes - many devices emit ultraviolet and it is extremely powerful, so appear even through covers, or use open electric heaters, which emit red.

Main lights I have seen there, where just ordinary fluorescent lamps, but I sure, on more modern fabs, used special lamps or color filters, to filter out part of spectrum which could cause unnecessary additional dose for photo-chemistry.

Not all lithography is Deep/Xtreme UV even in the newest fabs, because the equipment is so expensive and relatively slow. A lot of lithography is done the old way and is sensitive to UV from any lights. Box to box processing is almost complete, but there are times when a box may need to be opened or exposed to ambient light.

So there are some pretty good reasons to not to increase uncontrolled UV light exposure.

It's because photoresist is sensitive to deep blue out to UV so you want to avoid that kind of light as wafers with photoresist applied but not-yet-exposed are running around in their robotic FOUPs through the facility.

It's exactly analogous to red safe lights used for film print photography.

And photoresist is not only UV sensitive, people have success on exposure it with just very powerful halogen lamps, which don't have much UV.

So at fabs, usually, main light is not powerful, or have some color filters.

Photoresist is UV sensitive.

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