Emerging needs for continuous flow FOUP transport

The transition to 300 mm wafers places new demands on material handling. Most significantly, wafers will be transported and stored in front opening unified pods (FOUP), and process tools will be fitted with SMIF ports to transfer wafers in and out of pods without exposure to the fab environment. A 25-wafer pod can weigh over 8 kg, and for economic and ergonomic reasons can no longer be carried by operators. Hoists and other robotic devices will transfer pods between the tool load ports and new overhead or floor-based automated material handling systems (AMHS). In addition to the increased weight, 300 mm pod volume is more than twice the volume of a 200 mm pod, doubling the space required to store an equivalent number of pods. Zero footprint overhead storage allows wafer lots to be kept close to the process tools and prevents an undesirable burden on floor-space required by stockers. Such local buffers shorten the arrival time and increase tool utilization, which can have significant financial impact. Another emerging trend is distribution of certain process steps to locations remote from the main fab, requiring a high capacity point-to-point pod transport suitable for penetrating firewalls and passing along nonclean areas. This paper defines emerging fab requirements, then explores the different AMHS technologies and how they best fit specific tasks. A relatively new concept for pod handling, continuous flow transport (CFT) is presented. The authors show how this concept can meet pod handling requirements, including high volume transport and zero-footprint buffering near tools. Typical AMHS configurations and CFT performance data are shown.