晶圓製造廠內暫存區管理之探討

Abstract

晶圓製造廠的生產管理上，在製品(WIP)存量之控制為一重要主題，適當 的在製品存量將可使生產週期時間(cycle time)縮短，並減少存貨持有成 本及晶片的損失。一個好的暫存區管理模式將可以有效地控制系統中在製 品的數量，除此之外，更可使每個工作站有順暢的運轉情形，不至於有暫 存區不夠大而造成無法讓工件流往下一工作站，導致機器停擺，或工作站 缺料而造成停工待料的情形。而且一般半導體生管研究文獻多不去考慮工 作站前的暫存區容量，這也是不合理之現象。本文中，提出兩種暫存區管 理模式來找出適當的暫存區容量，分別為個別型暫存區(separate buffer)及通用型暫存區(common buffer)兩種模式。本論文提出一個兩階 段(two-stage)的方法來找出適當的暫存區容量；在第一階段中，根據晶 圓生產特性，利用模擬技術、信賴區間概念以及等候理論，求出起始值； 第二階段中，利用模擬將起始值調整成適當的暫存區容量值，此值能讓系 統有較好的表現。本文亦將這兩種暫存區管理模式加以相互比較及分析， 進一步從這兩者中找出一種較適合晶圓製造的暫存區管理方式；從比較結 果得知，在本文的假設下，通用型暫存區管理模式較適用於半導體晶圓製 造廠。 In the wafer fabrication factory, controlling the stock of WIP (work in process)is an important issue. The proper stock of WIP can shorten the production cycletime as well as reduce the holding cost of stock and the loss of wafer. Asuitable buffer management model will be able to effectively control thequantity of WIP in system. Additionally, it makes each workstation work smoothlyand avoid block or starvation. However, previous researches of semiconductorproduction management did not consider the buffer size in front of theworkstation.Two buffer management models, "separate buffer model" and "common buffer model,"are developed to determine the buffer size in wafer fabrication. For these twobuffer management models, a two-stage approach is developed to determine theproper buffer sizes. In the first stage, the initial values of buffer sizes areselected with respect to the properties of wafer fabrication, simulationtechnique, concept of confidence interval, and queuing theory. In the secondstage, the initial values generated in the first stage are further adjusted toproper buffer sizes making the system perform better. The proposed two buffermanagement models are also compared and analyzed by using a primary experimentalstudy. From the results of the primary experimental study, "common buffermanagement model" is more suitable for the wafer fabrication factory within theproposed assumptions.