Sub fabs are not always about liquids/gases etc. Some fabs, especially bigger DUV fabs, use the sub fab to run their lasers so that scanners can be arranged on

Sub fabs are not always about liquids/gases etc. Some fabs, especially bigger DUV fabs, use the sub fab to run their lasers so that scanners can be arranged on the track in a sane way. edit: btw, almost all fabs I have seen have multiple clean floors. Even the sub fabs doing only plumbing work would maintain a clean environment. I'm guessing because thats cheaper than maintaining the interface which goes from clean to unclean environments.