以電泳法及重力法進行矽及碳化矽分離之研究

Abstract

「矽」是目前半導體工業不可或缺的原料之一，舉凡太陽能電池、電腦中的矽晶片、顯示器中的基材等，都需要大量使用矽原料。然而隨著半導體工業及太陽能工業的蓬勃發展，使得原物料「矽」的價格也水漲船高，成本的高漲也直接衝擊了相關產業的發展。因此本研究將利用重力法(Gravity)及電泳法(Electrophoresis)來分離矽(Si)及碳化矽(SiC)，以得到高純度的矽來回收使用。 目前矽晶棒的切割約有34%的損失(kerf loss)，這些損失最後都以污泥的方式被丟棄或是回收SiC粒子（切割用磨料）後丟棄。這些矽泥包含了矽晶圓粉末、SiC粒子、潤滑油或是乙二醇、切割線損耗的金屬等已知雜質。本研究的第一部分先將矽泥以酸洗作為前處理，同時探討不同的酸洗條件下，矽泥中金屬離子含量的變化結果，找出移除金屬離子之最佳條件，本篇研究利用硝酸(HNO3)作為酸洗液，當酸液濃度大於0.5M、體積比大於23 mL acid/mL slurry，可以移除矽泥中99.5 wt%以上之金屬離子。接著再回收矽泥中酸處理過後之固成分，以進行本研究之第二部分。 本研究之第二部分是則是利用重力合併電泳作用，來分離固成分中的矽及碳化矽。以蠕動幫浦將稀釋後的矽泥緩慢打入沉降槽中，並施以一外加電壓，利用不同成分在不同的酸鹼度環境下，粒子表面之zeta potential不同的特性，輔以不同大小之粒子，在重力場中所受重力不同的效果、不同之表面電位於電力場中受到電力牽引不同的效果來分離此二種粒子，在pH值為7、外加電場為5volt/30 cm、離子強度低於0.005M之溶液來進行分離，當進行一次電泳重力分離後，可將矽泥中矽含量由25 wt%提高至80 wt%。

Solar grade silicon material is important in the manufacturing of photovoltaic cells. There is about 34% kerf silicon loss during Si wafer slicing process. The slurry wastes include abrasive particles (SiC), lubricating oil (ethylene glycol), metals from cutting wire, and the kerf silicon fine particles. The recycle of the silicon from the cutting slurry could save the raw material used significantly. In the first part, we treat the slurry with acid washed, and determine the amount of metal content. At the same time, we observe the change of metal content in different condition of acid washing. And decide the best condition to remove the most metal component from slurry. In this thesis, we try to remove the metal component utilizing the nitric acid (HNO3), when the concentration of the acid is greater than 0.5M, the volume ratio of acid and slurry is great than 23, and mixing time over 40 minutes, we can remove 99.5 wt% of metal in slurry. In the second part, we separate the SiC from Si particles by Electrophoresis and Gravity force. We get the dry solid component after acid washing, and dilute the dry solid by water. We inject the diluted solution into the settling tank by metering pump. When particles settle in the tank, we apply the electric field in the solution. Finally, we discuss the effect on the separation in different pH value of diluted solution and different electric field strength in solution. In this thesis, we use the solution which the pH value is 7, the ionic strength is less than 0.005M, and also we apply the voltage 5V to the solution. We can increase the silicon content in slurry from 25wt% to 80wt% by the electrophoresis and gravity effect.