以圖案化藍寶石基板製作無差排缺陷氮化鎵的方法

Abstract

本篇論文提出如何使用複合式圖案化藍寶石基板成長無差排缺陷氮化鎵薄膜的方法。此複合式圖案化藍寶石基板上之週期性奈米結構採用電子束微影搭配濕蝕刻方式形成，並使用有機金屬化學氣相沉積成長氮化鎵薄膜。運用圖案化藍寶石基板之技術提升氮化鎵薄膜品質已經被普遍使用，各種降低差排缺陷密度之方法也已經被廣泛探討，然而目前還沒有一個技術可以讓磊晶在藍寶石基板上的氮化鎵薄膜完全無差排缺陷。有鑑於此，本文將深入探討圖案化藍寶石基板對氮化鎵薄膜的影響，並提出如何使用藍寶石基板製做出完全無缺陷氮化鎵薄膜的方法。 研究的方法包含使用業界最普遍使用的砲彈狀圖案化藍寶石基板，研究氮化鎵薄膜在磊晶過程中的變化。接著製作各種不同週期、大小、排列方式的圖案化藍寶石基板，探討不同圖案化結構對氮化鎵薄膜的影響。綜合上述實驗，最後我們提出複合式圖案化藍寶石基板的設計方法，成功解決氮化鎵薄膜的差排缺陷問題，製做出完美無差排缺陷的氮化鎵晶體。主要的原因在於，利用複合式圖案化藍寶石基板製造氮化鎵薄膜內部的應力差，可以讓差排缺陷轉往橫向移動並導引至晶體外部，此外還可以阻擋其餘由下往上竄的差排缺陷提升晶體品質。

This doctoral dissertation proposes how to use multi-patterned sapphire substrate growth dislocation-free GaN thin film. The periodic nanostructures on substrate were formed by E-beam lithography combined with wet etching process and GaN epilayers were grown by Metal-organic Chemical Vapor Deposition (MOCVD). Pattered sapphire substrates (PSSs) had been used generally to enhance the quality of GaN thin films, and various methods of how to reduce threading dislocations (TDs) density had been widely discussed, too. However, there is no technology that can growth GaN epilayers on sapphire substrate without any dislocation defects until now. In this dissertation, the relationship between various PSSs and quality of GaN thin film is investigated. In addition, this thesis proposes a method to fabricate dislocation-free GaN epilayers on sapphire substrate. The research methods in this essay involves the investigation the evolution of GaN thin films growth on commercial dome-shaped sapphire substrate (CDPSS) during epitaxy. Then, a variety of PSSs with different periods, sizes and arrangements were fabricated to inspect the effects of different pattern structures on the quality of GaN films. Based on the experiment, finally we propose a composite patterned sapphire substrate design method, solve the problem of dislocation defects in the GaN thin film successfully, to create a perfect GaN crystal without any dislocation defects. The main reason is that the internal stress difference in GaN epilayers grown on multi-patterned sapphire substrate, can shift the threading dislocation to the horizontal direction and let this dislocation move forward to the outside of the crystal. This horizontal direction dislocation, in addition, will block the other TDs further enhance crystal quality.