多晶矽是太陽能電池的主要原料之一。而氧在直接固化法生長多晶矽晶碇中是一個重要的雜質，會影響太陽能電池之效率與晶片強度。氧雜質之傳輸機制為(1)坩堝壁高溫放出氧(2)自由表面處氣化(3)固液界面上發生偏析現象。為了控制氧雜質於長晶過程中之分佈，本研究利用數值方法模擬修改後的直接固化法長晶爐，間接改變固液界面形狀、流場型態及氧雜質分佈。 結果顯示，DSS長晶爐修改前，其流場型主要有兩個渦旋，一個靠近自由表面，另一個靠近固液界面。而氧雜質主要累積在中心軸之區域。DSS長晶爐修改後的固液界面形狀較原始長晶爐之固液界面形狀凸向熔湯，導致流場分離為兩個渦旋，一個靠近坩堝壁，另一個靠近中心軸。最後造成氧雜質會集中於角落處。 Multi-crystalline silicon ingot is a major material for solar cells. Oxygen, one of the most important impurities in directional solidification system (DSS), influences the efficient of solar cells and hardness of chip. Transport of oxygen includes (1) dissolve from crucible (2) disappear from free surface (3) segregation in melt-crystal interface. We modify the furnace’s structure of DSS to change the melt-crystal interface shape, type of flow field and distribution of oxygen in the solidification process by numerical analysis. The result show that there are two vortices, one is near the free surface and one is near the melt-crystal interface, make the high oxygen concentrate on the center zone mainly before modify the furnace of DSS. There are two vortices, one is near the center and one is near the crucible wall, separate from one vortex and high oxygen concentrates on the corner between the melt-crystal interface and crucible wall due to the shape of melt-crystal interface of modified DSS furnace more convex than the shape of melt-crystal interface of standard DSS furnace .