原子層沉積二氧化鈦薄膜於p型結晶矽基板表面鈍化特性之研究

Abstract

本研究使用原子層沉積法（Atomic Layer Deposition，ALD）以四氯化鈦（TiCl4）和水（H2O）為反應前驅物在p型FZ矽基板上成長二氧化鈦（TiO2）薄膜，製程溫度分別為80、100、150以及200°C，探討於不同溫度成長二氧化鈦薄膜之成長速率、結晶性、薄膜成分以及在矽基板表面鈍化特性。實驗結果顯示，在製程溫度80°C成長的TiO2薄膜具有最佳的矽基板表面鈍化效果，但是隨著著製程溫度升高，TiO2薄膜表面鈍化能力大幅下滑。透過X光繞射儀分析得知，TiO2薄膜在製程溫度上升至150°C時產生結晶，此時薄膜表面粗糙度大幅上升，薄膜內O、H與Cl含量則明顯減少許多。 為了提升TiO2薄膜在矽基板的表面鈍化能力，將製程溫度80°C的試片持續進行150、250、350°C退火處理。然而實驗結果顯示，TiO2薄膜在矽基板的表面鈍化能力並無提升，反而隨著退火溫度上升而下降。藉由二次離子質譜儀分析得知，薄膜內O、H與Cl含量經過退火後並無增加，反而造成薄膜產生結晶，導致其表面鈍化能力大幅下滑。

In this study, titanium oxide（TiO2）films were grown on FZ p-type Si substrates by an atomic layer deposition（ALD）system with TiCl4 and H2O precursors at different temperatures（80°C, 100°C, 150°C and 200°C）. The crystal structure, surface roughness, composition, and effective minority carrier lifetime of TiO2 thin films were characterized by X-ray diffraction（XRD）, Automatic ellipsometer, Secondary ion mass spectrometer（SIMS）and Photo-conductance decay meter（PCD）respectively. The results show that a TiO2 film grown at 80°C by ALD is capable of providing stable and excellent c-Si surface passivation on undiffused p-type surfaces. The surface passivation properties of ALD TiO2 thin films depend on deposition temperature. The surface passivation ability decreases with the increase of deposition temperature. The formation of anatase phase in TiO2 thin films was found to be the reason for the deterioration of passivation ability of as-deposited TiO2 films. In addition, the passivation properties are attributed to a good chemical passivation combined with an increased field effect passivation by negative charges. The chemical passivation is associated with a decrease of recombination active defects through H atoms which diffuse to these defects during deposition. The Cl was the reason for the amount of negative charges within the TiO2 film. The SIMS measurement indicate that annealing can not increase O, H and Cl within the TiO2 films.