濕式化學蝕刻技術用於氮化鎵發光二極體藍寶石基板移除與圖案化藍寶石基板之製作

Abstract

近年來，利用半導體材料製造紅、黃、綠光發光二極體(Light emitting diode, LED) 已經有很大的進展。目前，以氮化銦鎵/氮化鎵(InGaN/GaN)為主的材料成功製出藍光LED，配合螢光粉製造出白光LED，宣告了以白光LED為照明主流的時代即將來臨。然而，為了未來的照明上的應用，進一步提升LED的外部量子效率是非常重要的課題。 在本篇論文中，我們成功的利用濕式蝕刻技術來製作圖案化藍寶石基板(Patterned sapphire substrates, PSS)以及藍寶石基板之移除(Sapphire removal)。在製作圖案化藍寶石基板方面，我們使用H2SO4：H3PO4 = 3：1做為蝕刻溶液，製造出三種圖案化藍寶石基板，實驗的結果發現高度為1.3 微米的圓柱形圖案化藍寶石基板LED在操作電流為20 mA的情況下，發光強度較傳統平面藍寶石基板LED還高出49 %。 為了製造出垂直式發光二極體(Vertical-electrode LED)，在藍寶石基板之移除方面，不同於目前常用的雷射剝離技術(Laser lift-off)，我們使用交替式蝕刻法以H2SO4：H3PO4 = 5：1以及2：1做為蝕刻溶液來執行藍寶石基板之移除實驗，而此方法能達到對藍寶石基板與未摻雜氮化鎵(u-GaN)有最佳的選擇性，蝕刻的速率比值 (Rsapphire / Ru-GaN) 高達15。未來可以利用交替式蝕刻法實際執行藍寶石基板之移除以製作垂直式發光二極體。

Recently, wide-bandgap semiconductors have been attracting great interest for applications to optoelectronic devices such as light-emitting diodes (LEDs), for last few years, InGaN/GaN-based blue light-emitting diodes (LEDs) have been successfully fabricated and following comes the epochal of white light LED. However, for future illumination applications, it is very important topic to further enhance the external quantum efficiency of LED. In this research, sapphire removal and patterned sapphire substrates (PSS) were fabricated utilizing wet chemical etching technology. A 3H2SO4：1H3PO4 volume mixture was used as the etchant to etch the sapphire substrates with 280 °C, and we obtain three different kinds of PSS LED. The experiment results indicate that 1.3 micron cylinder PSS LED has 49 % efficiency enhancement than conventional LED at 20 mA injection current. In order to fabricate vertical-electrode LED, unlike the common technology, laser lift-off, we tried the commutative etching method to do the sapphire removal experiments employing 5H2SO4：1H3PO4 and 2H2SO4：1H3PO4 as the etchant. The etching rate ratio (RSapphire / Ru-GaN) is achieved 15. We may fabricate vertical-electrode LED utilizing the commutative etching method to remove the sapphire substrates in the future.