以電解混凝法處理化學機械研磨廢水-影響因子及反應機制

Abstract

化學機械研磨廢水(Chemical Mechanical Polishing, CMP)技術，近年來由於半導體製程元件快速地發展，線寬不斷的縮小，因此對於能使晶圓全面平坦化的CMP技術越顯重要，而CMP製程不但會消耗大量的超純水，且會產生大量不易處理的廢水。而對於此一廢水目前實廠處理方面，大多仍以化學混凝法為主，然而隨著近年來台灣的半導體工業不斷發展，所需的用水量日益增加，因此對於水資源不易蓄留的台灣而言，此股大量的廢水勢必要回收使用，但以化學混凝處理後的出流水，由於加入的酸鹼藥劑與混凝劑等使其導電度偏高，使得此股水回收用途有限，故此、目前園區多數廠家，已開始以薄膜程序搭配前處理或後續單元，處理並回收CMP廢水。 但薄膜處理程序是對於規模較大的廠家而言，才具經濟效應，對於一般規模的廠家成本過高，所以除了多廠廢水合併處理的方法外，簡易且經濟方法的研發是相當重要的研究。電解混凝法即是其一，本研究將過去使用電解混凝處理CMP廢水之影響因子做一完整的整理；且對於電解混凝反應機制方面，以各操作條件、反應時pH時的相對物種，以及界達電位等參數，經綜合分析比較後，歸納出電解混凝程序處理CMP廢水中的兩個主要機制：一是陽極釋出的二價鐵離子，在表面的擴散區中，與被電場作用力吸引到陽極板表面的Silica顆粒，行電性中和作用，隨及附著在「孔蝕化」的陽極板上，形成污泥；另一機制是，釋出的二價鐵離子離開擴散區後，在溶液中會與水分子以及水中溶氧，反應形成Fe(OH)4－及Fe(OH)3等氫氧化物，此氫氧化物在溶液中會進一步形成水合的膠狀懸浮物質，能吸附Silica等污染物顆粒，並沉降到槽體底部形成污泥；藉由此兩反應機制可去除CMP中穩定懸浮的Silica顆粒。綜和各項影響因子與反應機制，且待後續電混模式確立後，對於小型簡易的CMP電解混凝處理單元於實廠的推行，將是一大貢獻。

Chemical mechanical polishing (CMP) has emerged as a preferred planarization technic in the manufacturing of multilevel integrated circuits. This process not only consumes large amount of ultra-pure water (UPW) but also produces great quantity of wastewater which is difficult to treat. With the continuous development in semiconductor industry, the demand for UPW is increasing skyrocketing. The most popular method for CMP wastewater treatment is chemical coagulation. Such a large quantity of water must be reclaimed especially in Taiwan because the water resources are getting scarce. The effluent of the chemical coagulation has high conductivity which limits its reuse substantially. Therefore, membrane processes combined with pretreatment or follow-up process such as ion exchange are generally adopted to furAug. busibher treat and reclaim the CMP wastewater. However, membrane process is too expensive for small plants. For this reason simpler and cheaper methods are explored. Electrocoagulation is one of the options. In this study, frm flocs. The second mechanism is that the Fe2+ form Fe(OH)3 and Fe(OH)4－ with water molecules and the oxygen dissolved in the solution. The hydroxide will further turn into a hydrated gelatinous suspension in the aqueous stream to remove the silica particles froactors affecting the operation and reaction mechanism of electrocoagulation are discussed. The experimental result shows that two reaction mechanisms are involved in the electrocoagulation process. One occurs near the anode electrode. The Fe2+ liberated from the anode combines with the silica particles that are attracted by static electricity to fom the CMP wastewater by complexation or electrostatic attraction, followed by coagulation. Through these two mechanisms the stable silica particles can be removed.