晶圓廠機台加工效率指標之建立及應用

Abstract

機台綜合效率（overall equipment efficiency, OEE）指標結合了機台生產良率 （quality efficiency, QE）、可生產率（available efficiency, AE）、操作效率（operational efficiency, OE）與速度效率（rate efficiency, RE）等四項指標，是一個廣為半導體業界用來評量機台生產力（productivity）的綜合指標，其中RE指標更是晶圓廠生產線管理者用來評量及監控機台是否維持在最大生產速度的一個常用指標。然而，RE指標容易受到生產環境的干擾，常無法準確評量出機台實際之速度效率，很容易喪失改善機台生產力的機會而導致機台產能降低及晶片生產週期延長。因此，本論文主要目的有二，其中之一是針對RE指標之缺失另提出一個適用於晶圓廠的加工效率 (running efficiency, RUNE) 指標來取代RE指標。RUNE 指標不僅不會受到生產環境的影響，且較RE指標更易找出造成機台生產速度異常降低的可能原因。本論文的另一個主要目的是提出一套RUNE指標的自動更新與管制方法。此方法不僅可針對不同處方（recipe）適時更新機台與機台各細部步驟的目標作業時間以隨時獲得即時的RUNE指標評量結果；另外，利用指數加權移動平均（exponentially weighted moving average, EWMA）管制圖監控機台RUNE指標，可以協助晶圓廠生產線管理者隨時將機台維持在最大生產速度的理想狀況。本論文最後以台灣某十二吋晶圓代工廠之機台為例，建立機台之RUNE指標及其EWMA管制圖，並利用問卷調查方法探討晶圓廠生產線管理者利用RE指標評估機台生產速度所可能導致之機台產能損失，以驗証本論文所提之RUNE指標確實較RE指標適合作為晶圓廠機台生產速度之評量指標。

Overall equipment efficiency (OEE) is a composite metric, which includes quality efficiency (QE), available efficiency (AE), operational efficiency (OE) and rate efficiency (RE). OEE is widely adopted in semiconductor manufacturing to assess and enhance the productivities of processing tools. The RE is a very popular index for fab managers to evaluate or monitor whether the processing tools keep their maximum production speeds. However, the RE is easily influenced by the production environment, and thus it can not be utilized to evaluate the actual production speeds of the processing tools. Consequently, the improvement opportunities and processing tool capacities are missed due to the biased measurement of RE. Therefore, this study develops a running efficiency (RUNE) to replace RE to help fab managers to keep the processing tools in their maximum production speeds. The RUNE is not affected by the production environment, and can be employed to identify the sources of equipment’s variations. Additionally, a RUNE management procedure is also proposed. The proposed procedure incorporates an automatic target-setting scheme to set the target production time of each recipe on every motion in equipment to obtain the updated RUNE value of equipment. An exponentially weighted moving average (EWMA) control chart is then utilized in the proposed procedure to monitor the RUNE value of equipment. A case study of a 300m IC foundry in Taiwan is utilized to obtain the RUNE values of tools and EWMA control charts of RUNE values to evalluate and monitor the production rate of tools. Finally, a survey is conducted to study the potential capacity losses of tools due to the biased RE measurement result. The RUNE is then proved to be more robust than RE, and thus can evaluate the true production speeds of the processing tools more accurately.