Development and implementation of an automated wafer transport system

The move to 300 mm wafers has prompted IC manufacturers to demand a reliable automated material handling system (AMHS). Hewlett Packard's Inkjet Supplies Business Unit has worked with a supplier to develop a system using overhead rails and vehicles with hoist mechanisms to perform direct-to-tool delivery of 200 mm podded wafers. The system is intended to increase throughput by providing just-in-time material delivery and improve safety by minimizing manual handling. The system has a near zero footprint, leaving valuable floor space for process tools. While the system was built specifically for 200 mm material, most of this effort is directly applicable to 300 mm systems, and tests on the new system are very promising. Tool-to-tool delivery time was approximately 38 s, and pod placement accuracy was satisfactory regardless of pod load or vertical hoisting distance. Long term reliability tests indicated mean cycles between interrupts (MCBI) per vehicle of approximately 3,286 cycles (where a cycle is a pod move from between tools). All but one of the incidents encountered during reliability testing were recovered in 1 minute or less. A third party failure mode analysis identified a small number of potential safety hazards, which the supplier is addressing. Our study also identified issues to be addressed prior to production implementation, including improved vehicle maintenance procedures and better methods of identifying, troubleshooting and resolving system errors. Further modeling and scenario testing may need to be performed to better estimate system benefits and potential integration issues for specific applications.