Overhead Hoist Transport System

Overhead hoist transport (OHT) and the automated material-handling system (AMHS) it's a part of move FOUPs between tools across the entire fab floor, suspended from ceiling-mounted rail — automating the fab-wide logistics layer that sits above and connects every individual tool's own local automation.

Running transport overhead, on a ceiling-mounted rail network, is what lets a fab's floor stay clear for the equipment, people, and local automation that actually need that floor space. A ground-level transport system carrying FOUPs between every tool in the fab would need wide, obstacle-free corridors competing directly with equipment footprints and foot traffic; OHT instead runs its entire rail network overhead, leaving the floor free for process tools, local robots, and personnel while still delivering FOUPs tool-to-tool across the full fab layout.

AMHS dispatch software has to solve a real logistics optimization problem continuously, deciding which of potentially hundreds of OHT vehicles handles which FOUP move at any given moment. A large fab might have dozens of tools simultaneously requesting carrier moves, and a limited fleet of OHT vehicles has to serve all of those requests efficiently — AMHS dispatch logic assigns moves to vehicles, routes them to avoid congestion on shared rail segments, and prioritizes urgent moves over routine ones, making the software layer as critical to the system's actual throughput as the physical rail and vehicles themselves.

OHT and AMHS together form the fab-wide equivalent of the local automation this project has already covered at the tool level — FI robots, mainframe robots, load ports — extending that same no-human-touch, fully automated handling principle from inside a single tool out across the entire fab floor.