多孔矽基板在抗反射層應用之研究

Abstract

在本論文中，我們針對抗反射層利用多孔矽反射係數的數值模擬進行研 究。依據數值模擬的分析，我們開發出在單晶矽中形成多孔矽的化學蝕刻液 (包含氫氟酸、硝酸及水)。我們都知道在半導體產業裡，氮化矽與二氧化矽 過去一向是用在抗反射層。然而，使用氮化矽與二氧化矽抗反射層將會提高 太陽能模組的生產成本，不利於低成本的光伏元件。在單晶矽的結構粗糙化 製程中，使用斑點蝕刻形成多孔矽的化學蝕刻是一種簡單、快速及低成本的 技術。在可見光波段，多孔矽的粗糙化結構更可大幅降低元件表面的反射 率。 在此研究中，我們成功地在矽(100)與矽(111)基材表面上製造出多孔矽的 粗糙化結構，並利用多樣的氫氟酸、硝酸及水的混合比例去最佳化蝕刻製 程。在研究中發現，硝酸在斑點蝕刻裡扮演了非常重要的角色。當硝酸比例 在混合溶液中低於 40%，多孔矽的粗糙化結構會成形。而硝酸比例在混合溶 液中大於 40%時，多孔性結構形成與一般平滑性的表面蝕刻會處於過渡狀 態。此時，細微的孔洞結構會均勻地分佈在晶圓表面，並使表面粗糙化。藉 由使用化學蝕刻液的方法，我們可以從裸晶上獲得降低至 0%的反射率。更進 一步地，我們可以在大尺寸(7.5x7.5cm2 )的矽(100)基材表面上成功地形成多孔 矽的粗糙化結構；並且與傳統使用電漿增強化學氣相沉積法所形成的氮化矽 與二氧化矽抗反射層相較，仍然可以保持較低的反射率。因此，我們認為使 用斑點蝕刻技術所形成多孔矽的粗糙化結構將會取代傳統的抗反射層。

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nitric acid is lower than 40% in volume, porous etching occurs. The transition between porous formation and polishing etching occurs when nitric acid content is lager than 40%. Pore size distributes uniform on the surface of wafer. Stain etching also provides the rough surface. After etching in the proper etchant solution, the reflectance of the bare wafer was reduced to 0%. We have also successfully formed porous layer in large size (7.5x7.5cm) Si (100) which has lower reflectance compared with conventional AR PECVD-Si3N4, and SiO2 .We conclude that stain etching porous silicon could be a promising replacement for the conventional AR coatings.In this dissertation, we numerically study the reflectance of porous silicon (PS) layer for antireflection applications. Based on the numerical study, we develop chemical etchant (HF, HNO3, H2O) to form PS layer on crystalline silicon wafer. As we all know, silicon nitride and silicon dioxide are well known antireflection coating used in semiconductor industry. However, the deposition of silicon nitride and silicon dioxide films increase the total cost of solar cell modules which is not suitable for low-cost photovoltaic devices. In the other hand, the chemical etching known as stain etching (SE) porous silicon is a cheap, simple and rapid technique for texturing single-crystalline silicon. In addition, porous silicon shows the remarkable low reflectance at visible light. In this study, we have successfully fabricated porous silicon layer on top of the Si (100) and Si (111) surfaces. We varied the proportion of the solution of nitric acid, hydrofluoric acid and water to optimize the etching process. We found that nitric acid plays a very important role in stain etching. When the proportion of the