奈米微氣泡浮除技術於半導體工業化學機械研磨廢水

Abstract

半導體業中之化學機械研磨（Chemical mechanical polishing，CMP）廢水中主要含有奈米級之矽氧化物懸浮微粒，其具有相當穩定分散的能力。目前大部分廠商多利用傳統之化學混凝/沈澱來處理，但這個方法需要建造大面積的沈澱槽，且需要較長的過濾時間來分離。溶解空氣浮除法的原理主要是將水及空氣儲存於高壓桶內。根據 Henry’s law，氣泡與液體的混合液經高壓釋放後，溶解於水中的空氣會再次形成更小的氣泡，在上浮過程中與顆粒接觸達到浮除的效果。本研究中除了應用浮除的技術之外，更加入奈米氣泡生成技術，增加與CMP廢水中二氧化矽等顆粒接觸的機會。實驗的進行並搭配實驗設計，採取2k因子設計及中央合成設計以求取更有代表性的數據及結果。根據資料顯示，單純調整廢水的pH值，是沒有任何的去除效果。而在浮除過程前先行添加活化劑(硫酸鋁或是氯化鐵)，以及添加捕集劑(油酸鈉或是CTAB)，皆可以有效地去除廢水中的奈米等級微粒。最後發現控制硫酸鋁在285 mg/L左右，CTAB在5 mg/L，可以控制放流水濁度低於5 NTU以下的程度，遠低於法規的標準。最後結果發現搭配奈米氣泡產生器的浮除技術可以對CMP廢水中的微細顆粒進行有效率的去除，但在顆粒與氣泡之間的接觸作用，仍有待進一步的學理探討。

Chemical mechanical polishing (CMP) wastewater in semiconductor manufactory is characterized as extremely stable dispersion of nano-size silica. Generally, coagulation- flocculation and sedimentation processes are employed by most of the semiconductor manufacturers in Taiwan. This treatment needed large area for the sedimentation tank and take long time to separate the precipitate and clean water. Dissolved air flotation was recognized as a method of separating particles in the early 1900s. Small air bubbles are formed by injection of pressurized recycle water into a flotation tank using special nozzles. In this study, we use dissolved air flotation (DAF) process combined Nanometer Bubble Generator (NBG) which can produces very small bubbles. This study is divided into four parts. The first section discusses in fundamental properties of CMP wastewater and nana-bubbles. The second section is devoted to control pH value by adding acid or base and recycle ratio (R). In this section we do not add any activator or collector. It is expected that there must be some relationship between operational parameters and removal efficiency. In the third section, we add both activator (aluminum sulfate or ferric chloride) and collector (NaOl or CTAB) to measure the removal efficiency. In the final section, this study will follow the conclusion of first two sections, and confirm the best dosage (activator and collector). All experiments are design in Design of Experiment (DOE). Use central composite design for the second and final section, and 2k factorial design for third section. Experimental data were input to Minitab software for analyzing and plotting. By DOE method, this study would have minimum trials and get complete analysis. It is found that CMP wastewater is very stable because of adding dispersant. Bubbles are at a size of 30 to 5000 nm. Bubbles diameter less than 100 nm was 25.3%, and less than 1000 nm was 86.1 %. It was quite obvious that particles are smaller than bubbles. Results in second section showed that pH value had no significant impact on removal performance, but the R did. In third and fourth sections, the result showed that the activator, both aluminum sulfate (150 mg/L) and ferric chloride (100 mg/L) had good removal efficiency (turbidity and SS). And combined the collector NaOl (10 mg/L) had lower TOC residual concentration. With proper chemical and dosage, here we used aluminum sulfate combined CTAB, had better removal efficiency (turbidity < 5 NTU, SS < 0 mg/L and TOC residual concentration < 10 ppm ). Finally this study verified that flotation technology combined NBG process show much potential for the treatment and possible reuse of CMP wastewater. But there are still some aspects didn't investigate about chemistry interface of the bubble and particle.