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    "name": "Butting taps",
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      "timestamp": "2026-09-23T23:18:20.176+00:00",
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      "content": "The gf180mcu process allows tap diffusion to abut mosfet source drain. \n\nThinking just about the doped silicon, this is a lateral parasitic diode - not extracted as a device and not connected.\n\nHowever, I think gf180mcu adds a salicide step to the diffusion to reduce resistance. This effectively creates a low resistance layer over all diffusion (not blocked) irregardless of doping.\n\nIf this is true, then abutting tap and mosfet source/drain are shorted.\n\nIn the pdk used for chipathon 2026, the magic tech file extracts abutting tap and mosfet source/drain as shorted, but the klayout tech file does not.\n\nDoes wafer.space use a modified klayout rule that shorts the abutting diffusions?\n\n@Leo Moser (mole99)",
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      "content": "Thanks @bailey for bringing this up.\n\nI assume this is the same situation as on ihp, correct?\nThere is definitely salicide being used in the gf180mcu process. There is also a salicide block (SAB) layer.\n\nYou're refering to this line in the magic tech file regarding butted taps: https://github.com/fossi-foundation/open-pdks/blob/aa3fc215a80d32437b8cca1cb3fdee819d18c4c9/gf180mcu/magic/gf180mcu.tech#L711\n\nAs far as I can see, the KLayout connectivity setup for LVS does not consider butted taps: https://github.com/fossi-foundation/globalfoundries-pdk-libs-gf180mcu_fd_pv/blob/035e6d1f4bf0acfb60606b056e7d2159cba30fef/klayout/lvs/rule_decks/general_connections.lvs#L25\nWhich seems to be an oversight. Do you think it makes sense to add the simple case of a butted tap, without considering SAB for now?\n\nBy the way, are you planning to use KLayout for LVS?",
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      "content": "In magic `vss` and `I_in` are shorted, but in klayout they are not.\u3000(old post stuck in queue).",
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      "content": "Whether butted taps extract as shorter is a bit inconsistent between magic/klayout and across PDKs.\n\nFor IHP I think they are now made to be shorted because IHP actually uses that in their standard cells ( i.e. they only connect the butted tap to power/gnd and rely on the salicide to conduct to the source ).\n\nOn sky130 I think they are not extracted as shorts ( although they actually are ) because the salicide is not great and you should never rely on it for anything.\n\nOn GF180 I'm pretty sure I've also seen them recommend to always contact both source & tap even for butted taps (although here the salicide is pretty good).",
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      "content": "Ignore me -- but my brain completed this as \"buttered taps\" which kind of sounds tasty \uD83D\uDE1B",
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