晶圓製造廠備用零件動態安全存量模式之建立

Abstract

由於半導體市場競爭日益激烈，如何創造最大的競爭優勢是各晶圓廠追求的目標。設備為晶圓廠最重要的生產要素之一，而備用零件則是設備維持正常運作不可或缺的因子，它主要供應設備日常保養及當機維修的需要；由於設備當機為隨機發生，無法預期掌握，一旦發生當機缺料，將發生相當高代價的當機成本，因此準備一備用零件安全存量乃晶圓廠目前維繫生產力的必要方法。 然而，目前晶圓廠的設備備用零件安全存量的訂定方法，普遍為設備工程師訂定，再由物料管理師檢查的作業模式，這種作業模式缺少對整體生產環境變化的敏感性與互動性。特別在生產環境高度變化的晶圓廠，由於對備用零件的需求變化掌控不全，影響安全存量的準備，致發生缺料當機的高成本，仍時有所聞，使公司的營運受到莫大的影響。 因此，本研究提出動態安全存量的思考模式，藉由動態安全存量修正機制的運作，以判斷備用零件安全存量是否已經漂移(Shift)，再搭配景氣指標加權因子、產能負荷加權因子、製程位置加權因子對傳統安全存量模式的修正，產生一個全新的動態安全存量值。如此，安全存量不僅可與生產環境互動，而且也將安全存量的資金資源集中於生產系統該保護的瓶頸，降低因缺料當機所引起的產能損失，提高訂單的達交率(On Time Delivery) ，提昇生產系統的整體績效。

The semiconductor market is in a highly competitive stage now, all the wafer fabs struggle to create their competitiveness. Equipment is one of the most important manufacturing elements and the spare parts, which are supplied for PM and trouble shooting are the indispensable factor for the running of equipment. Due to the random happening of equipment down, it is very hard to predict when equipment will be down. Furthermore, there will be much cost occurred when the equipment is down without spare parts. Therefore, wafer fabs usually prepare the safety stock of spare parts to protect the productivity from the equipment down caused by spare parts shortage. However, the way for wafer fabs to set up the safety stock is that the equipment engineer proposes the safety stock and the material planner review it. This kind of operation model lacks of the sensitivity and reactivity against the change of manufacturing environment. In particular, the wafer fabs whose manufacturing environment is highly changeable sometimes lose the control of the preparation of the spare parts’ safety stock that should be compatible with the changeable manufacturing environment. It unfortunately causes the equipment down without spare parts and impacts their business a lot. As a result, the paper proposes the thinking mode of dynamic safety stock. Through the running of the adjustment mechanism of dynamic safety stock model, the shift of the original safety stock can be recognized. A new safety stock will be generated by the dynamic safety stock model, which is composed of the business index factor, capacity loading factor , process position factor and the traditional safety stock model. Hence, the model not only make the safety stock highly correlated to the dynamic manufacturing environment but also focus the monetary resource on system bottleneck .The probability of equipment down caused by spare parts shortage will be significantly reduced to raise the on time delivery and the total system performance.