| 摘要: | 碳氟化物(PFCs, Perfluorinated Compounds)為全球溫暖化潛勢極高之氣體，且存活於大氣中之時間達千年以上，因此對於可能造成之地球溫暖化問題逐漸受到重視；而為有效控制日益嚴重之全球溫暖化現象，於1997年12月日本京都所召開的溫室效應氣體管制會議中，便將包括PFCs及CO2、CH4、HPFCs、N2O等氣體列為管制項目。PFCs的排放控制方式除了提高製程中之利用率外，尚可採用替代化學物、回收再利用和破壞削減等方法；而相較於替代化學物開發的不易、回收再利用的高成本，破壞削減是現階段控制PFCs之主要方法。本研究嘗試以實驗室規模之填充床式電漿反應系統，針對PFCs中最為穩定之物種CF4，進行非熱電漿處理，並藉由反應氣體組成、反應器形式(平行板式反應器及線管式反應器)、供電電壓及供電頻率等重要參數之控制，探討填充床式電漿技術對CF4轉化率、產物分佈及生成量的影響，並初步評估放電系統的能量利用效率，以提供未來實廠化操作之參考。配合半導體製程本研究中實驗設計之氣體組成為：CF4=500 ppm、Ar=4,000 ppm、O2=20%以及N2為balance，氣體總流量為300 sccm，於初步測試中瞭解Ar濃度的提高將有助於CF4之轉化效率，因此後續實驗中將Ar視為一添加氣體，提升其濃度至40%。實驗結果顯示平行板式反應器各操作參數(電極間距、電場分佈、施加電壓及輸入能量)間關係複雜，各參數間的變化彼此關連相繫，對於轉化CF4效率最佳操作點為電極間距落於1.4~2.0 cm間，其去除CF4之最佳效率可達33.5%，配合添加劑乙烯則可提高至42.6%；於線管式反應器中，發現增加填充BaTiO3之長度具有較佳之CF4轉化效率，且由於線管式反應器之放電能量較高，使得CF4之去除率可達48%，當添加劑乙烯加入系統中時則可提升至66.6%。就生成物之分布而言，CF4轉化反應之主要生成產物以CO2、COF2及CO為主，本研究已證實藉由BaTiO3填充床電漿反應器配合碳氫化合物添加劑(C2H2及C2H4)破壞CF4之技術深具發展潛力。 Due to rapid growth in semiconductor manufacturing process such as etching and chemical vapor deposition (CVD) clean over these years, innovative technologies are needed to reduce the corresponding increase in chemicals used like perfluorocompounds (PFCs) that would be emitted to the atmosphere. PFCs are a cause for concern because of their large global warming potentials relative to CO2 and of their long lifetimes in the atmosphere, often thousands of years. To meet Kyoto agreement requirements, the strategies available for controlling PFCs emissions include applying alternative chemicals, recovery/recycle systems, process optimization and abatement technologies nowadays. In this study, laboratory-scale plasma reactors (parallel plate reactor and coaxial reactor packed with BaTiO3) have been set up to evaluate the removal efficiency for CF4, the most stable species of PFCs. The operating parameters including applied voltage, applied frequency, gas composition, gas residence time and input power were also investigated. The experiments demonstrated that electrodes distances, electric field, applied voltage, gas residence time and input power relate to each other in the parallel plate reactor and 33.5% CF4 removal efficiency could be achieved under 2.0 cm electrodes distance and input power 99 Watt. As for the coaxial reactor packed with 30 cm BaTiO3, the CF4 removal efficiency reaches 48% due to the higher power deposition than that of parallel plate reactor. Adding hydrocarbon C2H4 into the influent gas stream would enhance CF4 removal efficiency to 42.6% and 66.6% for parallel plate reactor and coaxial reactor, respectively. At the same time, the major end products detected by FTIR include CO2, CO and H2O. |
