氮化鎵基板的開發與同質磊晶研究

Abstract

目前的氮化物光電元件大多成長於藍寶石基板上，然而這種異質磊晶會伴隨許多問題，如晶格常數與熱膨脹係數的不匹配、高缺陷密度、應力累積與基板翹曲等。本論文主要研究目的是開發氮化鎵基板，並利用氮化鎵基板進行同質磊晶，以期解決異質磊晶的缺點。 在開發氮化鎵基板的部份，利用氫化物氣相磊晶法成長氮化鎵厚膜，並使用雷射剝離法製備獨立式氮化鎵基板。接著，利用氫化物氣相磊晶法在獨立式氮化 鎵基板的正面與背面再成長氮化鎵厚膜，以改善晶體品質與增加基板厚度，並改 變基板的翹曲程度。此外，利用乾式蝕刻的方式，大幅改善獨立式氮化鎵基板的 翹曲程度，曲率半徑明顯從1.5公尺增加到17.8公尺，使後續研磨與磊晶製程良 率與效率提高。 在利用金屬有機化學氣相沉積法於氮化鎵基板進行同質磊晶的部份，首先利 用乾式蝕刻與化學機械研磨的方式，消除氮化鎵基板因為研磨而產生的損害層， 再利用兩階段成長法進行未參雜的氮化鎵薄膜磊晶。最後在氮化鎵基板上成長的 高品質氮化鎵薄膜，差排密度大約是7x106 cm-2，X光搖擺曲線的半高寬在(002) 與(102)方向大約是92秒與54杪。

Currently, III-nitride devices are almost grown on sapphire substrates owing to their reliability and cost. However, their performance is limited due to the heteroepitaxy which accompanies various issues, such as lattice mismatch, the difference of thermal expansion coefficients, high dislocation density, biaxial stresses, wafer bow, and so on. The main objectives of this dissertation are the development of GaN substrates and the study of homoepitaxial growth on GaN substrates. On the part of developing GaN substrates, the GaN thick films were grown by hydride vapor-phase epitaxy (HVPE) and separated from the sapphire substrates utilizing the laser lift-off (LLO) technique. Then, the GaN thick films were regrown on the Ga- or N-faces of freestanding GaN substrates to improve the crystal quality, substrate thickness, and wafer bow. Furthermore, the dry etching method was applied here to significantly reduce the wafer bow of freestanding GaN substrates. The bowing radius of a freestanding GaN substrate can be significantly increased from 1.5 to 17.8 m by ICP etching. It can further improve the fabrication efficiency and yield of the polish and chip processes. On the part of homoepitaxially growing III-nitride layers on GaN substrates by metal-organic chemical vapor deposition (MOCVD), the GaN substrates were first treated by the methods of dry etching and chemical-mechanical polish (CMP) to diminish the damage layer caused by mechanical polish (MP). And the undoped GaN thin films were homoepitaxially grown on GaN substrates by two-step growth. Overall, low dislocation density of 7×106cm-2; narrow (002) and (102) XRD FWHM of 92 and 54 arcsec can be obtained by homoepitaxially overgrowing GaN thin films on GaN substrates.