Dispatching in Semiconcotor

Dispatching in Semiconcotor - Int J Adv Manuf Technol...

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Int J Adv Manuf Technol (2006) 28:978-984 DOI 10.1007Is00170-004-2431-x Muh-Cherng Wu Y.L. Huang Y.C. Chang K.E Yang Dispatching in semiconductor labs with machine-dedication features Received: 20 July 2004 / Accepted: 27 September 2004 / Published online: 15 March 2006 Springer-Verlag London Limited 2006 Abstract This research develops dispatching algorithms for a fab with machine-dedication characteristics. Machine-dedica- tion, a new feature in a modern fab, has not been addressed in previous studies of dispatching. Three performance indices, including hit rate, mean cycle time, and throughput are of con- cern in dispatching. This research develops an algorithm, called LB-SA, based on a proposed simplification model of the pro- cess route. The line balance (LB) component aims to smooth the flow rate of the process route; and the starvation avoidance (SA) component aims to ensure that the bottleneck machine is not "starving" and has enough work-in-progress (WIP) to process all the time. Thirty dispatching algorithms, including the LB-SA algorithm, are compared by simulation. The LB-SA algorithm outperforms the other 29 algorithms both in terms of hit rate and mean cycle time, and is only slightly less than the best bench- mark in throughput. Of the 29 other algorithms, one algorithm, called CR-SA, also performs very well. These two algorithms are both recommended for fabs with machine-dedication feature. Keywords Dispatching Machine-dedication Semiconductor Stepper 1 Introduction Semiconductor manufacturing is a process to make integrated circuits (IC) on a wafer. Wafers are transported in a lot, which typically includes 25 wafers. The factory, called a fab, includes hundreds of machines, categorized into several groups of work- stations. The process route of a product involves hundreds of op- erations, with a re-entry characteristic. That is, before its comple- tion, a product may enter a workstation several times. A fab may produce several products simultaneously. Therefore, the types of work-in-process (WIP) waiting at a workstation are highly M.-C. Wu (ES~) Y.L. Huang Y.C. Chang - K.E Yang Department of Industrial Engineering and Management National Chiao Tung University Hsin-Chu, Taiwam R.O.C. E-mail: mcwu@cc.nctu.edu.tw varied. To effectively control a fab's operational performance, dispatching decisions are very important. Dispatching decisions for semiconductor manufacturing have been extensively studied. Most studies developed dispatch- ing algorithms for increasing throughput and reducing cycle time [1-5]. Some others [6-9] focused on reducing tardiness hit rate, in addition to improving throughput and cycle time. These studies have established significant milestones in semi- conductor dispatching. Yet, one characteristic of a modern fab, called machine-dedication, has been rarely concerned in previ- ous studies on dispatching. Machine-dedication is a feature associated with a stepper, a machine in a fab. A stepper mainly performs the exposure op- eration, which is to "photo-print" electronic circuits on a wafer. Stepper workstations, as well as exposure operations, may be
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Dispatching in Semiconcotor - Int J Adv Manuf Technol...

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