化學機械研磨廢水之電混凝沉澱操作參數及模廠操作最佳化之研究

Abstract

化學機械研磨(Chemical Mechanical Polishing, CMP)為現今積體電路與光電元件不可或缺的製程之一，其產生的大量稀釋研磨廢水的處理也成為不容忽略的問題。此股廢水具有顆粒微小、粒徑分佈狹窄、及穩定性高的性質。本研究之目的即是針對此股廢水之特殊性質，利用「電解混凝」處理程序，並設計一電極板(陽極為鐵板、陰極為不鏽鋼板)交叉上下排列方式組成之反應槽，形成彎曲流道來增加顆粒與極板間之接觸機率，藉此提升顆粒之去除效率。研究共分實驗室規模及模廠規模兩種，實驗室規模方面，研究乃以人工配製之研磨廢水以及國內某晶圓廠之氧化層研磨廢水為處理對象，利用不同操作條件，包括施加電流密度、水力停留時間、不同初始濁度、初始導電度、初始pH及不同極板數目進行實驗，探討各參數對於處理效果之影響與可能機制。模廠規模方面則利用實驗室規模以及模廠規模之實驗結果尋求最佳操作條件，並在相同之處理效果條件下，比較化學混凝程序及電解混凝程序之成本，探討電解混凝程序實廠化之可行性。 實驗室規模之實驗結果顯示，較高之電流密度、較長水力停留時間、較多之極板數及較低初始濁度均能使濁度之去除率增加，且操控之操作條件下人工廢水最佳之濁度去除效率可達到95%，實廠廢水更達到99%的效果，此外亦發現增加導電度雖可有效降低操作成本，但相對亦攜牲部份去除效率，操作時應評估一適當值。研究中並針對實驗室規模之結果提出以「庫侖電量」作為電流與水力停留時間之綜合參數，經實驗結果證實此參數與濁度去除率具有高度之線性關係，可用此關係決定電解混凝程序之操作參數值。 模廠規模則已確定電流密度為1.92 A/dm2，流量為1.5 L/min，pH值、導電度不調整以及極板數20塊為最佳操作條件，且此條件處理水水質與化學混凝程序相當，以此結果比較成本，發現電解混凝程序與化學混凝程序之成本相差不大，需利用其它方法減少操作成本，但污泥產量方面卻可減少一半，因此仍有實廠化之可能，未來仍需以更大規模之設備評估研究之。

Chemical-Mechanical-Polishing (CMP) is one of key process in the manufacturing of integrated circuit and opto-electrical devices. The ultrafine particles contained in the CMP wastewater are difficult to remove due to the narrow size distribution and high stability. This study, therefore, is to focus on the application of the continuous-flow electrocoagulation process, including a laboratory-scale and a pilot-scale system, for separation of the highly charged particles from the CMP wastewater. The purpose of the laboratory-scale study was to investigate the effects of important operating parameter on the removal efficiency of turbidity using synthetic “oxide-CMP” wastewater. These parameters included the current density, hydraulic retention time (HRT), initial wastewater turbidity and conductivity, and the number of electrodes. The best operation parameters determined from the laboratory-scale study were then applied to the pilot-scale system for treatment of actual CMP alkali wastewater from a semiconductor fab. Upon further optimization of the parameters, the operating costs were estimated and compared with chemical coagulation process at the same level of turbidity removal to evaluate the feasibility of the full-scale operation. The results from the laboratory-scale study show that higher current density, longer HRT, more electrodes, and lower initial turbidity, generally improved the removal efficiency of turbidity. Removal efficiency up to 99% for the synthetic CMP wastewater was achieved. The “Coulomb equivalence” was used to serve as a comprehensive design parameter to correlate the operating current density and HRT with the expected turbidity removal efficiency. Furthermore, the operating costs could be substantially reduced by increasing the conductivity of wastewater, although this strategy required compromise of the removal efficiency. In the pilot-scale study, the optimum operating conditions were 1.92 A/dm2 for current density, (176 mins) for HRT, and 20 electrodes. No modification of wastewater pH and conductivity was needed. The effluent qualities as well as the operating costs were similar to those treated by chemical coagulation process. However, the sludge volume was reduced by as much as 50%.