5 ms·

Let me tell you a story about sulfuric acid. When I was working process integration at a fab, I had a long series of meetings about qualifying a new source of

Let me tell you a story about sulfuric acid. When I was working process integration at a fab, I had a long series of meetings about qualifying a new source of sulfuric acid. Not a new supplier even, nothing that risky. Just a new source, meaning the iso (tanker truck) full of sulfuric comes from a different plant owned by the same chemical company. What it comes down to is that it's basically impossible from a process integration perspective. Sure, you can take assays, and you do. But what about the things you aren't looking for in your assays? All you can do is plug it in, cross your fingers, and look at the yield trends. Not only does sulfuric mix in the supply lines, it gets used throughout the entire process. So if you do have some kind of strange contaminant that you didn't test for, maybe it only actually hurts you pre-gate. And the damage ramps up slowly and unevenly. But if your yield tanks, then you have to scramble to figure out what happened, and sulfuric isn't even your first suspect. (Because there are thousands of things like this that can tank your yields.) What's worse, you're literally over a barrel. Sometimes Plant A has to shut down and can't send you another iso. Do you take an iso from (unqualified) Plant B? Do you crack open a barrel of sulfuric? You have a stock of qualified sulfuric in barrels, for situations like this, but in practice barrels are worse than isos. Metal everywhere. I'm not saying it's sulfuric in this case. Lots of chemicals have a story like this one, but it would also not surprise me one little bit.

parimm 8y ago
Wouldn't using multiple Spectrometry/Spectroscopy methods help in finding out the impurities in the process chemicals? ICP-MS and NMR should cover most elemental impurities.
- Const-me 8y ago
  I don't have any experience working in that industry. But based on what I know, modern ICs require exceptional levels of purity of the materials. A single atom can ruin a transistor, and therefore the complete chip. AFAIK the methods you mentioned aren't sensitive enough to detect individual atoms in barrels of stuff. E.g. ICP-MS detects 1E-15 concentrations, but in absolute numbers, 1E15 molecules is only 1.66e-9 mole, e.g. for iron (55.8g/mole), it translates to 1E+10 defects per kg of stuff. Way too many.
  - dchichkov 8y ago
    Wouldn't you be able to run the test multiple times and increase your sensitivity to an arbitrary level? Too expensive?
    - lostmyoldone 8y ago
      Studied a fair bit of chemistry, but not a pro, so this is only a rough outline. A lot of chemical test equipment use semiconductor sensors of some kind - optical or otherwise - and most likely the sensitivity limit is simply the noise floor of the sensors. In good instruments they tend use good, or amazing detectors but they are still operating at the noise floor, or sometimes even below. So running tests again doesn't really help sensitivity, for that you would most likely have to use some chemical process that amplifies the effect of the contaminants you are looking for. Hence the problem of having to know what to lool for in validating new chemicals, if you need ultra pure chemicals.
  - twtw 8y ago
    > and therefore the complete chip. Most semiconductor companies bin chips based on how broken they are. GPUs, for example, frequently have different skus with the same chip differentiated by how many processors are broken (and thus disabled).
- sevensor 8y ago
  Elemental impurites aren't what we were worried about. It was organics. How sure are you there's no weird bacterium that lives in sulfuric acid and likes to eat iso tank lining? Would you bet $100 million against it?
natch 8y ago
Why don’t they have in house labs for creating all their chemicals? Seems like the investment would pay off.
- shaki-dora 8y ago
  - Those labs would run into the same sort of problem. It’s not like the supplier is contaminating on purpose. In-house would also produce less, making the staff less experienced - Chemicals aren’t created from thin air (although that is one ingredient). You will still have products coming in, only now you are one step closer to, say, raw oil, which has far more natural variation than the refined product you previously bought = the secret to, like, half our wealth is specialization. Doing complicated stuff as a side hustle in-house just isn’t our economy works.
- sevensor 8y ago
  We're not talking about a couple of people in white coats here. It takes a full-on chemical plant to supply enough sulfuric to satisfy a fab, and unless you're going to throw a ton of stuff away, this plant is going to produce a lot of other chemicals that are of no interest to the fab. That's not to say a vertically integrated conglomerate couldn't own both a fab and a chemical plant -- this is the rule rather than the exception in Japan and Korea -- but these are two separate industrial concerns.
samcday 8y ago
This is absolutely fascinating. Do you have any recommendations for books/videos/articles that shed more light on some of the interesting minutiae of cutting edge fab processes?
- sevensor 8y ago
  I'm afraid not -- I learned what I know through direct experience. That being said, I haven't really gone out there and looked for resources since I got out of the wafer business. Also, "cutting-edge" made me smile a little bit; this particular issue was mostly about plumbing :)

parimm 8y ago

Wouldn't using multiple Spectrometry/Spectroscopy methods help in finding out the impurities in the process chemicals? ICP-MS and NMR should cover most elemental impurities.

Const-me 8y ago
I don't have any experience working in that industry. But based on what I know, modern ICs require exceptional levels of purity of the materials. A single atom can ruin a transistor, and therefore the complete chip. AFAIK the methods you mentioned aren't sensitive enough to detect individual atoms in barrels of stuff. E.g. ICP-MS detects 1E-15 concentrations, but in absolute numbers, 1E15 molecules is only 1.66e-9 mole, e.g. for iron (55.8g/mole), it translates to 1E+10 defects per kg of stuff. Way too many.
- dchichkov 8y ago
  Wouldn't you be able to run the test multiple times and increase your sensitivity to an arbitrary level? Too expensive?
  - lostmyoldone 8y ago
    Studied a fair bit of chemistry, but not a pro, so this is only a rough outline. A lot of chemical test equipment use semiconductor sensors of some kind - optical or otherwise - and most likely the sensitivity limit is simply the noise floor of the sensors. In good instruments they tend use good, or amazing detectors but they are still operating at the noise floor, or sometimes even below. So running tests again doesn't really help sensitivity, for that you would most likely have to use some chemical process that amplifies the effect of the contaminants you are looking for. Hence the problem of having to know what to lool for in validating new chemicals, if you need ultra pure chemicals.
- twtw 8y ago
  > and therefore the complete chip. Most semiconductor companies bin chips based on how broken they are. GPUs, for example, frequently have different skus with the same chip differentiated by how many processors are broken (and thus disabled).
sevensor 8y ago
Elemental impurites aren't what we were worried about. It was organics. How sure are you there's no weird bacterium that lives in sulfuric acid and likes to eat iso tank lining? Would you bet $100 million against it?

natch 8y ago

Why don’t they have in house labs for creating all their chemicals? Seems like the investment would pay off.

shaki-dora 8y ago
- Those labs would run into the same sort of problem. It’s not like the supplier is contaminating on purpose. In-house would also produce less, making the staff less experienced - Chemicals aren’t created from thin air (although that is one ingredient). You will still have products coming in, only now you are one step closer to, say, raw oil, which has far more natural variation than the refined product you previously bought = the secret to, like, half our wealth is specialization. Doing complicated stuff as a side hustle in-house just isn’t our economy works.
sevensor 8y ago
We're not talking about a couple of people in white coats here. It takes a full-on chemical plant to supply enough sulfuric to satisfy a fab, and unless you're going to throw a ton of stuff away, this plant is going to produce a lot of other chemicals that are of no interest to the fab. That's not to say a vertically integrated conglomerate couldn't own both a fab and a chemical plant -- this is the rule rather than the exception in Japan and Korea -- but these are two separate industrial concerns.

samcday 8y ago

This is absolutely fascinating. Do you have any recommendations for books/videos/articles that shed more light on some of the interesting minutiae of cutting edge fab processes?

sevensor 8y ago
I'm afraid not -- I learned what I know through direct experience. That being said, I haven't really gone out there and looked for resources since I got out of the wafer business. Also, "cutting-edge" made me smile a little bit; this particular issue was mostly about plumbing :)