<title>New methodology for dynamic lot dispatching</title>

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This paper presents a new dynamic dispatching rule to improve delivery. The dynamic dispatching rule named `SLACK and OTD (on time delivery)' is developed for focusing on due date and target cycle time under the environment of IC manufacturing. This idea uses traditional SLACK policy to control long term due date and new OTD policy to reflect the short term stage queue time. Through the fuzzy theory, these two policies are combined as the dispatching controller to define the lot priority in the entire production line. Besides, the system would automatically update the lot priority according to the current line situation. Since the wafer dispatching used to be controlled by critical ratio that indicates the low customer satisfaction. And the overall slack time in the front end of the process is greater compared to that in the rear end of the process which reveals that the machines in the rear end are overloaded by rush orders. When SLACK and OTD are used the due date control has been gradually improved. The wafer with either a long stage queue time or urgent due date will be pushed through the overall production line instead of jammed in the front end. A demand pull system is also developed to satisfy not only due date but also the quantity of monthly demand. The SLACK and OTD rule has been implemented in Taiwan Semiconductor Manufacturing Company for eight months with beneficial results. In order to clearly monitor the SLACK and OTD policy, a method called box chart is generated to simulate the entire production system. From the box chart, we can not only monitor the result of decision policy but display the production situation on the density figure. The production cycle time and delivery situation can also be investigated.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.