藉由熱循環和應力集中從藍寶石基板剝離氮化鎵技術

Abstract

發光二極體(Light emission diodes,LED)具有高發光強度和節能的特性，因此被廣泛應用於在許多地方，例如:路燈、汽車頭燈、以及螢幕背光板等日常生活用品上。目前主要用來生長氮化鎵發光二極體的基板為藍寶石基板，而圖型化藍寶石基板(Patterned sapphire substrate,PSS)常被用於改善光取出效率以及內部量子效率。但是藍寶石基板為不好的散熱和導電材料，必須透過雷射剝離(Laser lift-off)的技術轉移至高散熱的基板製作出高功率的發光二極體。其中雷射剝離設備昂貴並且會損傷磊晶層，導致元件內部缺陷增加並使漏電流產生。所以本實驗題提出一個新的方式剝離氮化鎵磊晶層。 本次實驗使用凹型圖案化藍寶石基板(Concave-PSS)，經過磊晶成長後，成功的在基板與磊晶層介面處留下孔洞，使接觸面積減少方便後續的剝離製程。並利用晶圓接合技術將試片接合至高散熱的銅基板上，並藉由熱膨脹係數的差異進行高低溫熱循環，使熱應力集中於氮化鎵與藍寶石基板的接觸面，使其剝離並附著於銅基板上。透過化學蝕刻的方式分析剝離後的氮化鎵，找出其蝕刻優先順序與磊晶品質的關係，且將蝕刻後的特定晶面計算出為{101 ̅1 ̅}晶面族。

GaN-based light-emitting diodes(LEDs) have high luminous intensity and energy-saving features, so LEDs have been utilized in many places, such as streetlights,mobil headlamps and screen backlight sources. The performance of GaN-based LEDs which grown on sapphire substrates are inferior in terms of high-power applications. In order to improve the efficiency of LEDs, patterned sapphire substrates(PSS) have been widely used.However, sapphire substrates are thermally and electrically insulating, so we have to replace for a better substrate by using laser lift-off technique(LLO). LLO still have some disadvantages such as expensive equipments and damage epitaxial layer.Therefore, we propose a easy method to lift off GaN epitaxial layer. By using Concave-PSS substrates, the periodic voids remain between the interface of GaN and Concave-PSS. It can reduce the contact area and is conducive to subsequent processes. Then using wafer bonding technique to bond it onto Cu subtrate. Due to the 34% difference of GaN and sapphire substrate's coefficient of thermal expansion(CTE), thermal stress concentrate at the GaN/Sapphire interface to lift off GaN from Concave-PSS during thermal cycle process. Finally, we figure out that the etching priority is related to crystal quality by chemial etching process and calculate the specific etching facet is {101 ̅1 ̅}.