Semi E87

SEMI E87 is the standard for carrier management — it defines how equipment tracks a FOUP's identity and state over SECS-II/GEM messaging, from the moment E84's physical handshake confirms a pod is seated through carrier ID reading, slot-map verification, and state transitions like docked, open, and departed. Where E84 only ever answers "is it safe to move the pod right now," E87 is what actually knows whose pod it is, what's in it, and whether it matches what the host expects.

The carrier state machine exists because a FOUP's "identity" is really a sequence of trust-building checks, not a single read. A wrong or unreadable ID tag, a slot map that doesn't match what the host's MES expects (missing or extra wafers versus the lot record), or a carrier left in an undefined state after an error all need distinct, named states so the host can react correctly — a carrier stuck in Mapping means something different, and needs a different response, than one stuck in WaitingForHost. E87 defines the vocabulary for exactly which situation a port is in, which is what lets MES dispatch logic make correct decisions instead of guessing from raw sensor data.

Slot mapping is the step that catches the mismatches a visual check would miss. The equipment's mapping sensor scans every slot in the FOUP — not just confirming a wafer is present, but confirming the count and positions match what the host's lot record expects — because a partially unloaded carrier, a wafer left behind from a prior step, or a simple miscount upstream would otherwise go completely undetected until some much later process step discovers the discrepancy. E87 treats this mismatch as its own named error state (commonly MappingError) specifically so it halts the lot rather than letting it continue on bad assumptions.

E87 and GEM's event-reporting mechanism are tightly coupled, because every state transition in the carrier state machine is itself a GEM collection event. When a carrier moves from WaitingForHost to Mapping, or from Mapping to CarrierComplete, the equipment reports that transition using the same S6F11/S6F12 collection-event mechanism GEM defines generally — E87 doesn't invent a new reporting mechanism, it just defines which specific events and states matter for carrier tracking, layered on top of the general-purpose GEM event system.

Between them, E84 and E87 are what let a fab trust its own automation: E84 guarantees a pod was physically handled safely, and E87 guarantees the host actually knows what that pod contains and where it stands — split the two apart and a fab either can't move FOUPs reliably or can't trust what's inside the ones it moves.