晶圓廠控擋片降轉決策

Abstract

在半導體廠生產過程中，控擋片是用來監測製程品質是否穩定的工具，特定製程的控片使用後可以降轉給下級的製程控片使用，降轉的路徑會有多重選擇，控片降級決策的目的是要決定每條路徑的降轉數量，過去關於降轉決策的研究主要在最小化短期內的控片花費。 本論文發展一個線性規劃模式來做控片降級決策，以最小化長期的控片花費，經由控片成本分析發現用量成本遠大於存貨成本，因此本研究假設可提高安全存量來吸納短期的需求變異，則降轉決策問題便可簡化成靜態網路流量平衡問題，可利用線性規劃來求解，此靜態降轉決策的方法大幅簡化了現場管理的複雜度。

Control/dummy (C/D) wafers are metrology materials for measuring the process quality in semiconductor fab. C/D wafers of a particular process, after use, may need to be downgraded to one of several downstream processes. The decision of downgrading C/D wafers is to determine the quantity for allocating to each downstream process. Previous studies solved the downgrading decision problem on a short-term basis, which aimed to maximize the short-term C/D wafer costs. This thesis develops a linear programming model for the downgrading decision to maximize the long-term C/D wafer costs. An analysis of the cost items of C/D wafers reveals that the usage cost is much higher than the inventory cost. Therefore, this research assumes that the safety stock of C/D wafers is so highly prepared that it can absorb the short-term demand fluctuation. The downgrading decision problem is simplified to a static network balance problem and can be solved by the proposed linear program. This approach, a static downgrading policy, greatly simplifies the management complexity of shop floor operation.