Abstract
This thesis investigates the release control rule for the operation with queue-time-limit in semiconductor wafer fabrication. There are only a few researches on this subject before. This study compares two release control methods – simulation-based control rule, queue estimate control rule. The objective is to reduce the number of rework and increase throughput rate. This study experiment the above two rules under different level of the queue time limit and production rate. This thesis uses a third method – all release rule – to represent the situation without control rule and compares the above two control rules. The simulation-based control rule proposed by Tu 【2005】 builds a simulation environment similar to real environment and determines whether a lot will be processed within the queue time limit if the lot is released at dispatch time. The queue estimate control rule proposed in this thesis is based on the Queue Management proposed by Leachman 【1988】. This method is to estimate the queue length of the workstations on the route of the evaluated job. Comparing the queue length and the queue time limit will decide if the evaluated jobs should be released or not. The experiment of study research shows that the rework times of the job can be greatly reduced and the throughput can be largely increased by using proper releasing control . The simulation-based control rule outperforms the other rules under various conditions. The queue estimate control rule under low machine loading is not better than the third method – all release rule. In high machine loading, the queue estimate control rule is as good as the simulation-based control rule.