以電化學法處理化學機械研磨水

Abstract

化學機械研磨(Chemical Mechanical Polishing, CMP)技術以有效率全面平坦化的訴求符合生產極為快速的製程，並成為近十年來半導體及光電製造業中成長最為快速的單元之一。然CMP研磨液漸增的使用量以及普遍率不但消耗了大量的超純水外， CMP廢水中包含了奈米級研磨砥粒以及界面活性劑，使得CMP廢水顆粒形成極負電位、顆粒粒徑微小及分佈狹窄等特殊性質。一般半導體廠在處理CMP廢水時，不外乎是以傳統混凝沈澱、薄膜分離或甚至是直接排放的策略，而各種處理方法皆有其操作上的困難或是不合乎環境規範的問題，因此其產生的研磨廢水漸漸地對環境造成了負面的影響。 本研究中，以商業化之氧化矽研磨顆粒作為混凝沈澱改善、電解混凝與電解層析實驗評估的對象，並以約70 NTU的濁度模擬工廠廢水之排放濃度。結果發現氫碳酸鹼度能有效的穩定混凝沈澱的操作，並且經由線上光學膠羽偵測儀之連續動態監測可理想的控制混凝程序。另外，利用3片陽極鐵板與2片陰極不□鋼板所構成流道式的電解混凝系統，在不同的操作的電流密度及停留時間下，評估其電流效率以及濁度顆粒去除率的關係。實驗中發現以誘導電極之電解混凝系統能將濁度去除率提昇至92.5%，並且有低導電度出流水與相當少量鐵膠羽污泥的優勢。另外也發現到隨著操作電流密度與停留時間的增加，電解吸附混凝對CMP懸浮顆粒的去除效率越高，且其與法拉第第一定律中總電量有良好之線性關係。而於評估電解層析系統不同操作參數下的濃縮效率後，發現越高的電流密度及停留時間下，可達約4.4倍的濃縮效率及約90%之出流水濁度去除率，並且回收研磨砥粒的顆粒粒徑分佈沒有明顯的改變。因此，相對其他處理方法為研究CMP研磨顆粒的去除效率，電解層析法則有適用於超純水與研磨砥粒回收方面的可行性。

Because of its capability to achieve both global and local planarization that meets the increasing stringent lithographic requirement, Chemical Mechanical Polishing (CMP) has become an integral process in the manufacturing of multi-level integrated circuit device in recent years. Due to the nature of CMP process, however, an enormous quantity of ultra-pure water is required and thus large volume of dilute spent slurry that contains nano-sized particles and surfactant is generated. Presently, vast majority of IC fabs still use the traditional chemical coagulation and membrane separation processes to treat the ultra-fine, narrowly-distributed size, and highly-stable suspensions in CMP wastewater. As a result, wastewater treatment system often causes operational problems and gradually clashes the environmental regulations. In this study, synthetic CMP solution prepared by mixing commercial Cabot SS-25 slurry with DI water to a turbidity of 70 NTU was used for chemical coagulation, electro-coagulation, and electro-decantation experiments. In the modified chemical coagulation experiment, the settling characteristics of the CMP wastewater electrolytically pretreated were significantly different from that without electrolytic pretreatment. Additionally, bicarbonate alkalinity and photometric dispersion analyzer (PDA) detector were useful tools for optimization of chemical coagulation conditions. For electro-coagulation experiments using a channelized reactor with stainless steel cathodes and iron anodes, particle removal efficiency up to 92.5% was achieved. The effluent stream was also characterized by low conductivity and ferric floc content. Furthermore, the particle removal efficiency increased with the current density and retention time, and formed a distinct linear relationship with Faraday capacity. For electro-decantation experiment using stainless steel anode, particle removal efficiency up to 90% was achieved under high current density and long retention time. More importantly, the solid density ratio between the decanted sediment and the original slurry reached as much as a value of 4.4, demonstrating the potential application of slurry recycling or possible reuse by the electro-decantation process.