A Study of Rework Strategy for Photolithography in Wafer Fabrication Factory
D. Y. Sha
|關鍵字:||晶圓再加工;母批;子批;總加工時間;在製品存量;機台利用率;模擬;wafer rework;mother lot;child lot;total production time;WIP;utilization rate;simulation|
In the wafer fabrication factory, a fraction of the batch, or lot may require reworking because its members fail to conform to standards. It is usually unable to rework when a defective batch happened. In photolithography area, it is possible to deal with these defective batches. After defective batches reworked, the cost may be reduced. In batch manufacturing, it is important to deal with these batches when reworking happened. The issue of this study is to compare with the policies expressed in references and find another policy to deal with these nonconforming members. There are four policies to deal with defective batches in references. The first, the mother lot is held back while the child sub-lots are reworked. The second to the forth, the mother lot is allowed to proceed to the next operation, and the child lot be a new lot or cumulate to a quantity or join to the next mother lot. Some shortcomings are in above policies such as the management problems about mother lots and child lots and the economic to manufacture. This study introduces the fifth policy to avoid these shortcomings. In the fifth policy, mother lots and child lots are completed after reworking. Additionally, it is not necessary for mother lots to spend time waiting for child lot, and can follow the economic rules. From the simulation and statistic tests, the fifth policy is more suitable for the wafer fabrication factory when reworking happened.