The evolution of automated material handling systems (AMHS) in semiconductor fabrication facilities

The semiconductor industry has increased the size of wafers from 150mm to 450mm to improve productivity. This change has necessitated the need for innovations in the sizes of FABs, equipments, and transportation systems. the increase in the size of FABs, in particular, has resulted in many changes in transportation systems. The increase in wafer sizes has led to an increase in Front Opening Unified Pod (FOUP) weight, reducing manual handling by operators and bringing to light the importance of automated material handling systems (AMHS). The transportation systems of FABs can be largely divided into intra-bay and inter-bay. The initial 150mm FABs relied only on Overhead Shuttles (OHS) for automatic inter-bay transportation, while the 200mm FABs added Automatic Guided Vehicles (AGV) for automatic intra-bay transportation. The 300mm FABs introduced a segregated approach where high-speed Overhead Hoist Transports (OHT) are used for intra bay transportation and OHS’s are used for inter-bay transportation. The inefficiency of operating intra-bay and inter-bay transportation in a segregated manner in 300mm FABs has recently been raised, so a unified approach where OHT’s are used for both intra- and inter-bay transportation has been developed. Also, Side Track Buffers (STB) and Under Track Buffer (UTB) have been installed on OHT rails to minimize the footprint of stockers, resulting in minimal equipment rundown and reduced turn-around time (TAT) of semiconductor production. The standard for 450mm fabs is currently being heavily discussed within the International Sematech Manufacturing Initiative (ISMI).