| 摘要: | 碳氟化物對於地球溫暖化之貢獻量及其因應之道是近年來深受世人矚目的環境問題之一。在1997年12月日本京都所召開的溫室效應氣體管制會議中將CO2，CH4，HPFC，PFC（Perfluorinated compounds,全氟化物），SF6，N2O列為管制氣體。PFC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、回收再利用和處理削減等方法；而相較於替代化學物開發的不易、回收再利用的高成本，處理削減是現階段較易著手之研究方向。本研究嘗試以實驗室規模之介電質放電系統，針對佔PFC排放比率甚高之CF4及C2F6進行低溫電漿處理，並藉由反應氣體組成、濃度、供電電壓、供電頻率、氣體流量、停留時間及氧氣含量等重要參數進行控制，探討介電質放電系統對CF4及C2F6之轉化率和產物生成量及選擇度之影響，藉以瞭解PFC之轉化行為模式，以提供未來實廠化操作之參考。實驗結果顯示，於添加氧氣之介電質放電系統中，CF4及C2F6之轉化率隨供電電壓、供電頻率及氣體停留時間上升而增加，但隨CF4及C2F6進流濃度增加而轉化率呈現下降之趨勢；當氣流中之氧含量增加時，CF4及C2F6之轉化率隨之上升，然而過量的氧氣將不利於C2F6之轉化。當供給電壓為15 kV、操作溫度為25℃、停留時間為13.7秒、結合觸媒填充床、氣體組成為[CF4]/[O2]/[Ar]/[N2] = 300 ppmv:20 %:40 %:40 %時，所獲得之CF4轉化率為65.9 %；當供給電壓為15 kV、操作溫度為25℃、停留時間為13.7秒、結合觸媒填充床、氣體組成為[C2F6]/[O2]/[Ar]/[N2] = 300 ppmv:10 %:40 %:50 %時，所獲得之C2F6轉化率為94.5 %。就生成物之分布而言， CF4、C2F6轉化反應之主要生成產物以CO2、COF2為主；隨轉化系統之供電頻率增加時，CF4、C2F6轉化反應之生成產物除了CO2、COF2外，亦有CO生成；於結合觸媒之轉化反應中，CF4轉化的產物主要以CO2為主，而C2F6轉化後的產物則包括CO2、CO。本研究已證實介電質放電系統配合添加氧化劑以轉化CF4、C2F6之技術確實可行，深具發展潛力。 Perfluorocompounds (PFCs) are widely used in the semiconductor industry for plasma etching and chemical vapor deposition (CVD). The global warming potential of these gases has triggered a significant effort to reduce their release into the atmosphere. In 1997, the Kyoto environmental regulatory council reached a consensus to abate CO2, CH4, PFC, SF6, N2O emissions. The ways to reduce PFC emission include applying alternative chemicals, recovery/recycle systems and abatement techniques. Effective reforming of CF4 and C2F6 with O2 as additive via dielectric barrier discharges (DBD) was experimentally investigated in this study. A laboratory-scale experimental system was designed and constructed to evaluate the reforming efficiency of CF4 and C2F6. The effect of operation parameters including applied voltage, applied frequency, oxygen concentration, gas residence time, and power input on the removal efficiencies of CF4 and C2F6 was investigated. Experimental results indicated that the removal efficiency of CF4 increased with application of higher voltage, O2 content, gas residence time, power input and higher frequency. C2F6 was also removed with a higher efficiency with application of higher voltage, O2 content, gas residence time, power input and higher frequency. However, removal efficiency of C2F6 was found to decrease if more than 10% of oxygen was applied. The conversion efficiencies of CF4 and C2F6 achieved with plasma combined with catalysts were significantly higher than those without catalysts. The major products of the CF4 and C2F6 processing were CO2, COF2 when O2 was included in the discharge process. When the system was operated at a higher frequency, CO was produced as well. The converting process of CF4 and C2F6 mainly produced CO2, but not COF2, for the system packed with catalysts. Experimental results indicated that reforming of CF4 and C2F6 with O2 as additive via dielectric barrier discharge was technically feasible. |
