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Notes -
Happy to answer any other questions. I really enjoy talking about this and find it equally as cool.
Fabs use a combination of bulk gases (N2, H2, O2, Ar, etc) and speciality gases (AsH3, PH3, SiH4, SiH2Cl2, etc) depending on the process. Bulk gases are fed from massive canisters and get distributed throughout the fab to points of use. The piping is normally located directly underneath the main fab floor in an area called the subfab to save space, increase convenience of maintenance, and prevent particles from contaminating tools. Speciality gases follow the same path from their source canister, but instead there are valve manifold boxes (VMBs) between the point of use and source to allow for safer operation and improved monitoring capabilities. MKS has a decent fab facilities overview here. (As a side note, welding gas lines is preferable to minimize the chance of leaks or contamination. This comes at the risk of the line being completely custom and having long leadtimes in case it needs to be replaced. I prefer parts to be as modular as possible so we can replace the part itself and not the entire subsystem with it.)
The process is controlled by the brains of the fab, the manufacturing execution system (MES). Some fabs build their own custom MESs to match their needs and others go with out-of-the-box solutions that have dedicated company support. Full-stack MESs generally handle most of the calculations when decided what to do, whereas not-full-stack MESs require other programs to assist.
Redundancy is crucial to a fab's success. We try to minimize OAK (one-of-a-kind) paths else everything grinds to a halt directly in front of that tool and I get yelled at for why my tool isn't up. Industrial engineers are able to model a fab's capacity abilities and determine how much of what technology is able to run given the number of available tools and their qualification status. For example, I have four tools (E1-4) and four technologies (T1-4). E1 can run T1-4, E2 can run T2 and T4, E3 can run T3, and E4 can run T1 and T4. Thus, T1 has two paths, T2 has two paths, T3 has one path (OAK alert!), and T4 has three paths. T4 material would likely be fine since it has three different options to run through. T3's OAK is a bit dangerous and unOAKing it should be a priority if its loadings (how much T3 we run) is high enough. To put it more simply, think of it as tolls: if there are 10 lanes and 10 consecutive tolls (so 100 stations total) and all of set1's tolls can handle Toyotas, but only one of set2's tolls can handle Toyotas, then Toyotas will get through set1 quickly but get really backed up at set2 because they're all forced to the same path that has a fixed throughput and may be dealing with other car brands! Some wafers require processing within a certain amount of time after finishing their previous process for various reasons (e.g., native oxides).
I will kindly abstain from answering this for opsec reasons :)
Thanks for the excellent response!
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