氧化層化學機械研磨廢水混凝加藥最適化之研究：pH控制法

Abstract

化學機械研磨製程一直是積體電路產業中大量超純水消耗的主因，同時也造成了大量的廢水排放。其中又以氧化層研磨廢水的產量最大，氧化層研磨廢水的之中含固態及溶解態的二氧化矽，傳統處理法以混沉處理為主，採用沉澱網除的過量加藥法，造成額外的加藥成本及污泥處理費用。本論文旨在提供一個線上控制邏輯，精確控制氧化層研磨廢水(oxide-CMP wastewater)混凝處理時的混凝劑線上加藥量。本論文主要以「pH控制法」(pH Control Approach)來決定線上加藥劑量值，其與傳統瓶杯試驗不同的是，其加藥邏輯可直接對線上加藥進行控制且毋須定期確認參數。pH控制法視混凝劑為酸滴定藥劑，直接對進流之氧化層研磨廢水進行加藥，及至特定pH時，加藥停止，此時之加藥量即為電性中和去穩之控制點，遠較過量加藥法經濟。依pH控制法的原理可採pH計或濁度計皆可作為加藥控制的基礎。pH控制法的使用與廢水進流濃度及加藥槽之混凝劑儲備濃度完全無涉，故本研究結果不因於廢水進流濃度的變化而產生不能適用的情形，且不同之混凝劑，如鐵鹽、鋁鹽、多元氯化鋁等均可適用。

CMP process is the main cause for the consumption of large quantity of ultra-pure water in IC industry. There are two kinds of CMP wastewaters: oxide- and metal- CMP wastewater. Between the two CMP wastewaters, the quantity of oxide-CMP wastewater is much larger than the other one. Conventionally, the treatment strategy for oxide-CMP wastewater is ”coagulation-sedimentation process”. Nevertheless, on-line control for coagulant dosing has not been developed yet. Additional cost for chemical usage and sludge treatment always exists. This paper discusses a method for on-line control on coagulant dosing for oxide-CMP wastewater treatment. The dosage is determined by pH control approach, which does not require a routine jar test. This method can simultaneously determine the optimal pH and economical dosage for oxide-CMP wastewater. The coagulant can be added directly into the raw water without the pH adjusting at first. According to this method, the coagulant acts like a titrant and the pH of the oxide-CMP wastewater is monitored. The optimal dosage is the one that corresponds to a specific pH. Moreover, base on the pH control approach, not only pH meter, but also turbidity meter can be applied in on-line dosage controlling. Since the method is independent of the concentration of the influent wastewater and the concentration of the stock coagulant, this method is unaffected by the fluctuation in influent wastewater concentration. In addition, it is applicable to other coagulants, such as poly-aluminum chloride, aluminum salts and iron salts.