BACKGROUND

Automated material handling systems (AMHS) have been widely used in semiconductor fabrication facilities (also termed as FABs) to automatically handle and transport groups or lots of wafers between various processing machines or tools used in chip manufacturing. A typical FAB may include a plurality of process bays including processing tools (e.g., a process tool) and wafer staging equipment.

Each bay may include a wafer stocker, which includes multiple bins for temporarily holding and staging a plurality of wafer carriers during the fabrication process. The wafer carriers may include standard mechanical interface (SMIF) pods which may hold a plurality of wafers, or front opening unified pods (FOUPs) which may hold larger wafers. Stockers generally include a single mast robotic lift or crane having a weight bearing capacity sufficient for lifting, inserting, and retrieving a single wafer carrier at one time from the bins. The stocker holds multiple SMIF pods or FOUPs in preparation for transporting a SMIF or FOUP to the loadport of a processing tool.

A semiconductor FAB may include numerous types of automated and manual vehicles for moving and transporting wafer carriers throughout the FAB during the manufacturing process. These may include for example manually moved carts, rail guided vehicles (RGVs), overhead shuttles (OHSs), and overhead hoist transports (OHTs). In an AMHS, an OHT system automatically moves OHT vehicles that carry and transport wafer carriers, such as SMIF pods or FOUPs holding multiple wafers, from a processing or metrology tool (e.g., process tool) or a stocker to the loadport of another tool or other apparatus in the FAB. The OHT system may be used to transport vehicles within each bay (intra-bay) or between bays (inter-bay). The OHT system also moves empty vehicles (i.e. without a wafer carrier) to the tool loadport or other apparatus for receiving and removing empty or full SMIF pods or FOUPs that may contain wafers for further transport and/or processing in other tools.

Handling and transport of wafers in an AMHS is typically built into a FAB and may not be easily adapted when processing machines or tools used in chip manufacturing are moved or changed in a FAB. However, typical manual handling and transportation of wafers also requires large overhead and is prone to human failure. Accordingly, an improved system and method for handling wafer transport in a semiconductor FAB is desired.

