透過原子層沉積鈍化層與製程改善提升藍光微發光二極體之效率與良率

Abstract

本研究所使用的樣品為外購商用之藍光波長磊晶片，研究目標在於製作微米等級的發光二極體（Micro-LED）。實驗內容涵蓋元件與光罩設計、製程參數優化、以及最終的電性與光學特性量測。我們的研究重點在於開發並提升1.5µm 與2µm超小尺寸元件的製作良率及效率，也期望在微縮尺寸的條件下仍能保持良好的發光效率。 在製程方面，我們首先於P型半導體表面沉積一層厚度約220nm的氧化銦錫透明導電層（ITO），藉此改善電流在流經元件的均勻性，並降低P型電極遮蔽發光區域的面積，進而提升出光效率。在耦合式電漿蝕刻（ICP-RIE）製程中，我們針對遮罩材料進行改良：過往使用光阻(S1813)作為蝕刻遮罩，但由於光阻硬度不足，在乾蝕刻後容易造成側壁蝕刻不均與損傷，導致元件側壁出現明顯缺陷，尤其在微米尺寸元件中影響更為顯著。本研究改以SiO₂作為遮罩，其較高的硬度與蝕刻耐性可有效抑制側壁損傷，獲得更平整且垂直度更佳的mesa結構。 乾蝕刻以及N型電極完成後，我們進一步在元件表面進行原子層沉積（ALD）以及電漿輔助化學氣相沉積（PECVD）兩步驟的介面與側壁保護。ALD技術的主要優點在於能以原子層級的控制精度並沉積高品質薄膜，具備極佳的均勻性與覆蓋率，特別適用於高深寬比的結構。其緻密的氧化鋁（Al₂O₃）薄膜能有效降低側壁缺陷密度、抑制表面再結合速率，與後續PECVD的氧化層（SiO₂）結合使用，可進一步形成多層鈍化結構，提升元件的可靠度與長期穩定性。

The experimental work in this study includes device and photomask design, process parameter optimization, and final electrical and optical characterization. The main objective is to develop and improve the fabrication yield of ultra-small devices with sizes of 1.5 µm and 2 µm, while maintaining high emission efficiency under the condition of device miniaturization. In terms of fabrication, a 220 nm-thick indium tin oxide (ITO) transparent conductive layer was first deposited on the surface of the p-type semiconductor to enhance the uniformity of current spreading through the device and to reduce the shadowing area caused by the p-type electrode, thereby improving the light extraction efficiency. During the inductively coupled plasma reactive ion etching (ICP-RIE) process, the mask material was optimized. In previous processes, photoresist (S1813) was used as the etching mask; however, due to its insufficient hardness, non-uniform etching and sidewall defects frequently occurred after dry etching, resulting in severe sidewall defects—an issue that becomes even more critical for micron-sized devices. In this work, silicon dioxide (SiO₂) was adopted as the etching mask instead. Its higher hardness and etch resistance effectively suppress sidewall damage and enable the formation of smoother, more vertical mesa structures. After completing the dry etching and n-type electrode deposition, the devices were further protected by a two-step passivation process consisting of atomic layer deposition (ALD) followed by plasma-enhanced chemical vapor deposition (PECVD). The major advantage of ALD lies in its ability to deposit high-quality thin films with atomic-scale thickness control, excellent uniformity, and conformality, making it particularly suitable for high-aspect-ratio structures. The dense aluminum oxide (Al₂O₃) film grown by ALD effectively reduces sidewall defect density and suppresses surface recombination. When combined with the subsequent PECVD-deposited silicon dioxide (SiO₂) layer, a multilayer passivation structure is formed, further enhancing device reliability and long-term stability.