Production Control in Parallel Multi-tool Systems under Sequential Process Queue Time Constraints
Date Issued
2014
Date
2014
Author(s)
Pan, Bo-Chen
Abstract
Production control in parallel multi-tool systems under sequential process queue time constraints is studied in this research. When WIP finished an upstream process step, the WIP should be processed at the next process step within a given amount of time. The time constraint is called the process queue time constraint. Any violation of the process queue time constraint seriously impacts yield quality and incurs significant scrap costs.
In the semiconductor industry, the violation of process queue time constraint may cause the wafer surface oxidation to be reproduced or scrapped. Under the sequential process queue time constraints and multi-tool production environment, the dispatching strategy is hard to be defined. Besides, machine reliability and demand uncertainties also make the production control difficult, production managers need to balance the need for achieving production targets and yield quality.
The Multi-step with Multi-tool Heuristic Control (MMHC) is developed to minimize long-run average production cost. The MMHC strategy is formulated with stochastic dynamic programming. The model objective is to minimize the sum of inventory holding costs and scrap costs. The simulation results reveal that our method significantly reduces total production costs.
Subjects
馬可夫決策過程
動態規劃
作業等候時間限制
啟發式演算法
Type
thesis
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