超純水系統 UV 光去除微量 TOC 效率影響評估

Abstract

由於近年來半導體等高科技廠製程技術提升改良與元件線寬精密化，超純水 (Ultra Pure Water, UPW) 的使用量與消耗量皆大幅提昇，相對衍生之超純水製造技術亦不斷在演進；一般半導體廠製程用水量約佔總用水量的 70% 左右，主要用於蝕刻製程清洗之用途。然而，製程環境中的超純水系統以及無塵室氣體環境中的超微量污染物都將關鍵性地影響製程良率，尤其是超微量的有機污染物 (trace organics)，90% 以上的製程不良率導因皆來自有機性污染物，因此超純水中對於微量有機物之去除與偵測為穩定控制超純水產水水質、提升製程良率之重要關鍵；一般而言，超純水中有機物質常以總有機碳量 (total organic carbon, TOC) 予以表示。 TOC-UV 為超純水製造系統中常見之單元，其主要功能為利用波長 185 nm 的紫外光 (Ultraviolet, UV) 達到超純水中有機物質降解的效果。本研究目的即為評估超純水系統對於 TOC 的處理能力，藉由量測超純水系統各處理單元出流水的 TOC 值瞭解超純水中微量有機雜質之變化，進一步透過調整 UV 反應器不同水量以及不同數量的 UV 燈管組照射之操作參數進行系統減費與效能測試 (examination and optimization)。另一方面，為了瞭解 TOC-UV 在超純水系統中段與後段對於 TOC 的去除效率，本研究分別挑選 M 廠與 P 廠之超純水系統進行測試與評估，協助本廠建立超純水系統各處理單元之水質資料 (TOC baseline)，並藉此完成 UPW 系統 TOC-UV 單元效能檢視與改善，以及後續降低運轉成本方案之研擬與評估。 研究結果顯示大約 70% 的 TOC 可在超純水製造系統中段被去除，其餘的部分再由後段的 TOC-UV 單元予以降解並移除，超純水系統後段主要功能為水質再精鍊 (polishing)；UV 系統減費與效能測試結果顯示單次通過 (one-pass) UV unit 的 TOC 去除率於 unit 內燈管全開與關閉 24 支燈管分別為 26.5% 與 12.4%；關閉 12 支燈管時，其 TOC 去除率與全開時差距縮小，但出流水的 TOC 值皆小於 1 ppb，即使於後段關閉三組 UV 燈組對於水質的影響幅度亦不大，由此可知超純水系統後段 TOC-UV 單元確實可減少設置數量，在不影響系統供水端水質的前提之下，經 UV 系統效能檢視與減費評估之後，確實可降低廠內超純水系統運轉與耗材成本，本研究獲得之數據與結果將可提供本廠作為運轉與年度歲修之參考。

The cost and consumption of ultra pure water (UPW) in the semiconductor industry has dramatically grown with advances in integrated circuit (IC) design. In addition to questions regarding the economics of UPW treatment, concerns have developed over the restrictions on the water supply and the environmental impact of contaminants in discharged wastewater. It has been suggested that, to help resolve such water usage problems, the wastewater from the rinse stages of IC manufacturing steps should be recycled and reused. Trace organics have been identified as the serious contaminant responsible for more than 90% of all micro-contamination problems that affect IC production yields. Since total organic carbon (TOC) accounts for a large proportion of the impurities found in rinsing wastewater, which is hard to deal with, utmost care should be paid to the TOC level.

The TOC-UV by 185 nm UV rays is the most representative unit in UPW system for reducing/degrading organics. The aim of this study is to on-site evaluate the performance of TOC-UV (185 nm) of UPW system. The values of TOC were measured at each treatment unit in order to obtain the TOC baseline. Furthermore, plant M and plant P were selected as the models to differentiate the removal efficiencies of TOC-UV units in the make-up system and the polishing loop, respectively. For the optimization and the examination experiments of TOC-UV units sizing, UV lamps and units were shut down in turns to assess the significance to TOC variations. At last, the cost for system operation and the maintenance, and the consumable parts replacement of UV units for the consideration in annual maintenance were also calculated.

The results reveal that up to 70% TOC were removed in the make-up system; the remaining TOC was further treated by the polishing loop in the UPW system. In addition, the increase in TOC values when UV lamps were turned off can be ignored due to the fact that TOC values were under the specification of 1 ppb during the optimization and examination experiments. The results can be useful for saving and reducing the running cost and the consumable materials replacement at the annual maintenance of plant M and plant P.