A Study of Rework Strategies and Dispatching Rules for Photolithography in Wafer Fabrication Factories
Lin Shih Hsing
Sha Yung Jye
|關鍵字:||晶圓製造;黃光區;良率;再加工;在製品水準;生產流程時間;交期;再加工策略 派工法則 模擬;wafer fabrication;photolithography;yield;rework;WIP;production flow time;due date;rework strategy dispatching rule simulation|
|摘要:||在晶圓製造中，由於晶圓的原料及機台成本昂貴，為了能夠增加晶圓的良率( yield )，利用再加工( rework )的方式來補救不良的晶圓為可行的措施。同時為了顧及生產中在製品水準量、產品生產流程時間、產品交期等目標，必須要有良好的再加工策略處理晶圓的再加工。晶圓在微影黃光區產生不良時可利用再加工方式補救，所以本研究討論在微影黃光區中幾種再加工策略，並與常用的派工法則配合，期找出最適的生產控制組合。
In wafer fabrication, the material of wafer and machine cost is expensive. To increase the wafer yield, defective wafers produced during the process need to be repaired as possible. However, rework of wafer is only allowed in the photolithography area of a wafer fabrication factory. If any defective wafer produced during the process which is not in the photolithography area ought to be scrapped. In addition, it is necessary to consider some important performance measures in a wafer fabrication factory such as WIP level, production cycle time, product due date…etc. Therefor, this study studies several rework strategies and dispatching rules which are often used in a fabs. The proper rework model is then suggested. In this study, five rework strategies and five conventional dispatching rules are discussed. The five rework strategies are: 1.hold the mother lot while the child lot is reworked, and then complete the lot before moving it to the next location. 2.proceed the mother lot, and introduce a new child lot into the facility after finishing rework. 3.proceed the mother lot, and introduce a new lot composed of numerous child lots when a predefined number of wafers have accumulated. 4.proceed the mother lot, and add the reworked wafers to the next mother lot of the same product. 5.proceed the mother lot, while reworking the child lot immediately and completing the lot in some latter process. Five dispatching rules: FIFO, EDD, SPT, SRPT, and CR+ are used. A simulation model is developed to determine the performance of the combinations of rework strategies and dispatching rules.