考量晶圓製造廠混合生產環境整體績效之生產活動控制方法

Abstract

記憶體生產與晶圓代工為半導體晶圓製造產業中的兩大主流，然而，近年來不少的DRAM製造廠由於產能過剩與DRAM價格持續低迷，而面臨轉型的壓力，欲進一步導入代工的業務以分散風險。此種生產環境即為存貨式生產（Make to Stock, MTS）與訂單式生產（Make to Order, MTO）混合之生產環境。一般而言，MTO較著重交期方面的績效，如平均延誤、生產週期時間與其變異等等；而MTS則重視產出量以及資源利用率等績效。混合生產環境由於兼具MTS與MTO之特性，因此必須提昇系統之整體績效，以達到規劃產出之目標及符合客戶需求。然而目前有關晶圓製造生產排程與控制之研究多針對單純MTS或MTO生產環境，並未就混合生產環境進行探討並提出相對應的生產規劃與控制方法，本研究的主要目的即針對晶圓製造廠混合生產環境構建適當的生產活動控制策略。 本研究以維護MTO產品之交期績效為首要考量，以使系統產出最大化及維護MTS產品平順產出為次要考量，運用限制理論瓶頸決定產出的理念，以及現場負荷控制與填充產能的觀念，發展一個能有效提昇系統整體績效的投料派工法則。在投料法則方面，首先依據各MTO訂單之交期緊迫程度排定其投料日程，而依據現場實際負荷狀況決定投料時機，並利用MTS產品填補系統剩餘之產能，以確保MTO產品能及時產出，並使系統產出最大及避免瓶頸資源缺料。在派工法則方面，依據MTO產品之生產進度以及MTS產品在製品分佈狀況，在瓶頸與產能受限工作站劃分四條虛擬等候線，以監控各晶圓批之生產狀況，作為動態調整各晶圓批加工優序之用，如此不僅可以提昇MTO產品與MTS產品之生產績效，亦有助於防止瓶頸漂移的發生。 模擬實驗之結果顯示，本研究針對晶圓製造廠混合生產環境所構建之生產活動控制策略，除了能以較少的在製品使系統產出最大化外，亦能維護MTO產品之交期績效，不僅可降低其生產週期時間、平均延誤，提昇其交期達成率，並且對於MTO產品之生產週期時間與延誤變異的控制，更具有其顯著的成效。至於MTS產品部份，透過本研究派工法則的監控機制，亦可有效提昇其產出率及控制其產出率的變異。

Memory and foundry are the two major product areas of Taiwan IC industry. However, owing to the overcapacity and decreasing price in DRAM business, many memory venders face the pressure to readjust their business focus. To lower the risks, some of them try to introduce the foundry business. When a wafer fabrication factory combines memory business and foundry business, it may produce products under Make-to-order (MTO) and Make-to-stock (MTS) hybrid production environment. Since MTS and MTO have many differences in production planning and control, a manufacturer in hybrid production environment must consider the differences and try their best to manage their production performance, such as the due date performance of MTO products and throughput rate of MTS products. The objective of this research is to develop an production activity control (PAC) method for wafer fabrication factories in hybrid production environment. The primary consideration of this paper is the due date performance of MTO products, then take maximization of system throughput and smooth throughput of MTS products as secondary consideration. This study construct a PAC method based on the concept of Theory of Constraint, workload control and capacity fill-up to improve overall performance in hybrid production environment. The release method first decides the release schedule of MTO products in consideration of their due date, then apply appropriate MTS products to fill up remained capacity, to ensure on time delivery of MTO products and maximize system throughput. As for dispatch rule, this method monitors progress of MTO products to avoid tardiness, and monitor WIP of MTS products at each stage in bottleneck and capacity constraint workstation to ensure smooth production of MTS products. From the experimental results, not only a lower WIP and higher throughput was obtained, but also due date performance of MTO products was improved. Concerning MTS products, the throughput rate and its variance was controlled effectively while applied the proposed WIP monitor and control mechanism.