CMP廢水中溶解矽於UF薄膜結垢之研究

Abstract

摘 要 隨著國內半導體產業逐漸進化至奈米級科技，化學機械研磨（Chemical Mechanical Polishing , CMP）為其製程進化至奈米化之重要關鍵技術，然目前CMP製程需耗費大量超純水，且產生之廢水較難處理，對於水資源有限之台灣環境而言，如能將其處理回收使用於純水前段，對工廠節水效能及製程廢水回收率將助益極大。 惟一般CMP廢水處理回收之處理系統中存在薄膜單元嚴重積垢問題，造成處理回收成本遠高於自來水水費，導致僅少數大廠有意願投入處理回收行列。故本研究希望能解決薄膜積垢問題，排除推廣CMP廢水處理回收之障礙，營造永續產業發展環境。 藉由國內外相關研究文獻整理後發現，薄膜單元積垢問題主要源於CMP廢水中矽化合物所形成，而其中以固態顆粒矽積垢行為研究居多，鮮少針對溶解矽酸所造成之積垢問題深入探討。因此，本研究將針對CMP廢水中溶解態矽酸對超過濾（ultrafiltration，UF）薄膜之積垢行為為對象，並參考實廠CMP廢水溶解態矽酸濃度之人工原水與高濃度人工原水，進行多組不同過濾時間實驗。 研究結果顯示， UF薄膜表面積垢程度會隨著過濾時間與矽酸濃度增加而有顯著之影響；溶解矽酸乃依顆粒顆徑成長及結垢方式造成薄膜阻塞；溶解矽酸除造成UF薄膜表面結垢，亦將穿越薄膜孔洞於纖維層中纖維形成結垢；溶解矽酸所形成之薄膜結垢，主要組成為Si、Si2O、SiO及SiO2等四項物種；溶解矽酸經由UF薄膜過濾時，隨著過濾時間愈久（積垢增加），pH值呈現加速下降之變化。建議未來除發展薄膜積垢清洗方式外，更需發展同時去除溶解矽酸與導電度、有機質之技術程序，為未來產業永續發展建立最有利條件。

As the domestic semiconductor industry is gradually progressing to nano-scale, chemical mechanical polishing, CMP, process plays a key role in the industry. The CMP process consumes plenty of ultrapure water and produces a lot of wastewater which is difficult to treat. Therefore, the wastewater reuse rate can be greatly increased and reduce the consumption of water, if CMP wastewater can be reused. Wastewater reuse is very important due to the limited water resources in Taiwan, especially the semiconductor industry contributes a major part of economy for the country.

The membrane filtration process is an effect way to recycle CMP wastewater. However, only a few semiconductor manufactories try to apply such a process because of the membrane scaling problem. The study is try to solve the problem and increase the wastewater recycle rate for CMP process.

According to extensive references review, it was found that membrane fouling mainly results from the dissolved silica in CMP wastewater. However, most of the studies focused on the fouling behavior of solid silica, few studies looked into the membrane fouling which is due to dissolved silica. This study attempts to investigate the fouling mechanism of dissolved silica by use of ultra filtration (UF) membranes. According to the concentration of dissolved silica in CMP wastewater, several filtration tests have been performed and high concentration of synthesized dissolved silica wastewater was also investigated in this study.

It was found that as filtration time and concentration of dissolved silica increased they both have a distinct effect on membrane fouling. Membrane fouling which was caused by dissolved silica is because of the growth of particle size and scaling. Dissolved silica not only results in membrane scaling but also penetrates into membrane pores and therefore, causes scaling in the support layer. The analysis showed that scaling which was caused by dissolved silica is mainly composed of Si, Si2O, SiO and SiO2. During the UF filtration of dissolved silica pH decreased with the elapsed filtration time which also increased membrane fouling. Besides, developing membrane cleaning technology is very important for reusing CMP wastewater. The development of removing dissolved silica, conductivity and organic matters simultaneously is essential for setting up the sustainability of the whole semiconductor industry.