- 學位論文
電解混凝沉澱程序處理半導體化學機械研磨廢水之研究
Electrocoagulation and Settled Process of Chemical Mechanical Polishing Wastewater from Semiconductor Fabrication
摘要
積體電路製程中的銅導線製程需要利用化學機械研磨(CMP)技術除去晶圓上多餘的薄膜，讓整個晶圓平坦化，但由於此項技術使用頻繁且需要大量高純水來進行晶圓清洗動作，所以屬於高污染的製程。從實際半導體廠取回的廢水中含有高界達電位(Zeta potential)的微粒、高懸浮固體濃度(SS)，超過排放標準的化學需氧量(COD)值以及銅離子濃度，造成環境污染與處理的困難。本研究利用電解混凝法(EC)，對實廠的化學機械研磨含銅廢水進行處理，並自行改良電解凝聚設備，另外，針對處理過程產生的污泥做沉降性質與脫水的探討。本研究也使用冷凍解凍法去除污泥中多餘的水分，達到污泥減量的目的。 在分析廢水水質實驗中，發現懸浮顆粒平均粒徑約為100 nm，界達電位-43 mV，COD高達370 mg/L、濁度在52~180濁度單位(NTU)之間，銅離子濃度為45~120 mg/L。本實驗探討各變因如電極種類、電聚時間、電流密度、電極板距離、鹽類添加量、混凝劑與助凝劑添加量等對處理效果的影響。由結果得知，使用鋁電極的效果最佳，在六片電極及電流密度382.2 A/m2等最佳條件下只需要電解混凝15 min，Cu-CMP廢水的濁度去除率達96.5%，使處理後上層液濁度小於1 NTU，COD去除率為75%，使廢水濃度低於50 mg/L以下，銅離子去除率約99%，排放水濃度低於1 mg/L，皆符合放流水標準，並可以回收再利用。 使用鋁電極所產生的氫氧化鋁，以及捕集的化學研磨顆粒，會產生大量的污泥，而污泥的沉澱速率將影響到沉澱槽的尺寸設計，實驗發現固定污泥沉降管柱的管徑/高度比就能控制同樣的沈降條件。另外，可以利用數學模式計算沉澱速率、固體通量與沉澱槽的尺寸關係，並發現Cho等學者所推導的3rd order model、4rd order model 以及complicated exponential model可以適切的描述污泥沉澱速率與污泥濃度的關係，亦可以此結果推估沉澱槽的尺寸。 本研究使用冷凍解凍法嘗試減少電解混凝Cu-CMP廢水後產生的污泥體積以及脫除污泥中的水分，實驗發現冷凍解凍法可以有效的將污泥脫水，電解混凝後污泥體積為215 mL，冷凍解凍後體積減至10.2 mL，總固體濃度則是從19.1提高至276.8 g/L，含水量由98.2減少至61%。結果證明冷凍解凍法可以有效的減少電解混凝法所產生的污泥體積與其含水量。
並列摘要
Treatment of Cu chemical mechanical polishing (CMP) wastewater from a semiconductor plant by electrocoagulation was investigated. The CMP wastewater, as obtained from a large semiconductor plant, was characterized by high suspended solids (SS) content, high turbidity (NTU), chemical oxygen demand (COD) concentration up to 370 mg/L, and copper concentration up to 120 mg/L. Conventional methods had difficulties in satisfactorily dealing with this wastewater. This study was to investigate the feasibility of treating the CMP wastewater by electro-coagulation with an aim to simultaneously lowering the wastewater turbidity, copper, and COD content. Experiments were conducted to assess the effects of electrocoagulation time and electrolyte dosage on the system performances. The test results revealed that the electrocoagulation with three Al/Al electrode pairs and current density 382.2 A/m2 was found to be very efficient and able to achieve 99% copper ion and 96.5% turbidity removal in less than 15 min. The COD removal obtained in the treatment was higher than 75%, with an effluent COD below 50 mg/L. This discharge wastewater could meet the water quality standard and the effluent of water can be considered for recycling. Sludge settling velocities after electrocoagulation were measured and the data were employed to validate the empirical sludge settling velocity models proposed. The sludge settling characteristic data was also utilized to establish the relation between the solid fluxes and the initial solids concentration. In addition, models fit of the observed sludge settling velocity data indicates that the complex models, including the 3rd order, 4th order, and these of Cho et al. (1993), describe the data significantly better than the simple power and exponential ones alternatives. Finally, the solid fluxes determined the settling velocity curve shows a skewed distribution and the solid fluxes curve facilitates design of the sludge settling tank. Low-temperature treatment of sludges generated from Cu-CMP wastewater was investigated. Freeze/thaw conditioning effectively dewaters sedimentary sludge obtained from the electrocoagulation of Cu-CMP wastewater. This study was to explore the feasibility of treating sediment of electrocoagulation method by freeze/thaw conditioning process with an aim to decrease sludge volume. After freeze/thaw conditioning, the sludge volume ranged from 215 to 10.2 mL. Total solid concentration increased from 19.1 to 276.8 g/L and moisture of the sludges decreased from 98.2 to 61%. Bonding energy of moistly sludge solids was also estimated according to these experimental data. In addition, the effect of flocculation on the moisture distribution of the sludges was revealed. These results indicated that the freeze/thaw conditioning technique is a practicable technology for treating sludges generated from Cu-CMP wastewater.