半導體晶圓廠化學供應區酸性氣體污染改善研究

Abstract

半導體晶圓廠製程日益精進，使無塵室生產環境的潔淨度要求，由管制微粒（Particle）的數目進而管制氣態分子污染物（Airborne Molecular Contaminations, AMCs）的濃度，因此微污染控制成為半導體廠房建置的關鍵技術，當供應系統保養或維修操作不當時，容易造成生產製程使用的化學品與特殊氣體（Special gas）產生酸、鹼與有機類的氣態分子污染物，本研究使用平板濕式固氣分離器（Parallel plate wet denuder, PPWD）輔以離子層析儀，採樣分析半導體晶圓廠化學供應區的酸性氣態分子汙染物，並研究改善作業標準程序，以減少作業時氣態分子汙染物產生。

改善控制污染源研究分為鹽酸供應系統保養作業汙染改善，與氫氟酸化學桶更換作業汙染改善。鹽酸供應系統保養作業改善前採樣濃度4,616ppbv，接近國內TLV-STEL管制標準5ppm，並大於固定污染源空氣污染物排放標準（周界）0.1ppm，僅靠化學供應區的整體換氣，需超過2小時以上，才能將殘留的鹽酸氣態分子汙染物完全移除；故設計一個移動式隔間局部排氣設備，保養作業時採樣濃度0.4ppbv，作業完15分鐘後採樣濃度降為0.15 ppbv，可見適當的使用移動式隔間局部排氣設備，確能有效捕集鹽酸氣態分子汙染物，且能快速將擴散到環境的汙染物移除。

氫氟酸化學桶更換作業改善前採樣濃度為42ppbv，經過1小時後採樣濃度8ppbv，僅靠環境整體換氣，需2小時以上，才能將氫氟酸濃度降至2ppbv以下；針對化學供應系統的設計條件，設定三個變因進行改善汙染實驗，(1)變因一：供應系統內部箱體增加負壓抽氣點(風速0.2m/s)；更換作業時採樣濃度為29ppbv，顯示變因一對於更換作業時蓄積箱體內的汙染物移除有些微影響。(2)變因二：供應系統的高效濾網送風關閉；僅打開箱體外門時採樣濃度為14ppbv，更換作業時採樣濃度為120ppbv，顯示變因二無助於汙染物移除，且反而增加更換作業時產生的汙染物擴散至環境。(3)變因三：化學桶開口與抽風罩開口的相對位置，由垂直改為平行；更換作業時採樣濃度為1.9ppbv，顯示變因三能有效將氣態分子汙染物移除，並且避免擴散出環境。

The clean room standard was controlled by the number of particles; it is controlled by the concentration of Airborne Molecular Contaminations (AMCs) due to the advanced semiconductor wafer manufacturing process. Therefore, it is critical for the semiconductor fab constriction to control AMCs. When the supply system is not properly maintained, the AMCs of acids, alkalis, and organic compounds are likely to be produced. The parallel plate wet denuder (PPWD) and Ion Chromatography‎(IC) are used to analyze the AMCs in the chemical supply area of the semiconductor fab in this study. The improvement of standard operational procedures to reduce the AMCs is also discussed.

There are two scenarios in this study. Scenario 1 is the improvement of HCI supply system maintenance pollution. Scenario 2 is the improvement of HF drum replacement work pollution. The sampling concentration before operating the improvement scenario 1 was 4,616 ppbv which is closed to the national standard TLV-STEL of 5ppm. It is also within the AMCs pollution standards of 0.1ppm. A mobile compartment local exhaust equipment was designed for the study; its concentration was 0.4ppbv after the maintenance. The concentration was reduced to 0.15 ppbv after operating for 15 minutes. Therefore, it is indicated that an appropriate use of mobile compartment local exhaust equipment can effectively capture HCl pollutants, and can promptly remove contaminants.

The improvement scenario 2 is HF drum replacement work pollution. The sampling concentration before operating the improvement scenario 2 was 42ppbv. The concentration was reduced to 8 ppbv after operating for one hour. It takes two hours to reach the concentration at below 2 ppbv by changing the environment. There are three different variables in this study. Variable 1: Increasing the negative pressure exhaust (the wind velocity of 0.2 m/s) in the supply system internal cabinet; its sampling concentration was 29ppbv. The result shows that variable 1 has a slight effect on the removal of internal cabinet contaminants. Variable 2: Switching off the supply system HEPA air supply; its sampling concentration was 120ppbv. The result shows that variable 2 has no effect on the removal of internal cabinet contaminants. Nevertheless, it increases the probability of the environment pollution. Variable 3: Changing the position of chemical drum and hood openings from a vertical direction to a parallel direction; its sampling concentration was 1.9ppbv. The result shows that variable 3 can effectively remove contaminants and prevent from spreading to the environment.