本實驗主要是為探討濕式蝕刻於氮化鎵磊晶層上之運用，因目前為提升光萃取效率而對氮化鎵磊晶層進行表面粗化，以及化學濕式剝離法等皆會於氮化鎵磊晶層上進行濕式蝕刻，有鑑於此方面研究並未有完整探討極整理，故於研究我們運用不同的蝕刻溶液以進行濕式蝕刻來蝕刻在藍寶石(sapphire)基板上的氮化鎵無摻雜層(un-doped GaN)，並探討不同的蝕刻溶液、溫度及時間下對蝕刻深度和表面形貌的影響。
    本實驗所運用的氮化鎵磊晶層是以有機金屬化學氣相沉積法(Metal-organic Chemical Vapor Deposition, MOCVD)進行磊晶成長於藍寶石基板上，因本實驗選用之藍寶石基板為c軸方向，因此氮化鎵磊晶的方向為沿著c軸成長，而因不同蝕刻溶液對不同極性面有不同的蝕刻現象，因此本論文將對濕式蝕刻之機制做深入的探討。
    研究上發現氮化鎵磊晶層上進行濕式蝕刻會與其蝕刻能障係數相關，而當蝕刻能障係數大於m-plane時則無法被蝕刻出也無法觀察到，蝕刻上不論運用酸或鹼蝕刻液其蝕刻出平面主要以(10(11) ¯)為主。

This study use the different etchants to do wet-etching process on the un-doped GaN epi-layer on sapphire substrate. We investigate in detail about the depth and morphology by different etching conditions.
    In this experiment, metal-organic chemical vapor deposition (MOCVD) was used to regrow un-doped GaN on sapphire substrate. And then, c-plane GaN epi-layer was used to the basic substrate for etching study. The different polarities face have respective phenomenon in etching process. Therefore, this study will discuss the different etching behaviors of GaN epi-layer.
   Finally, we found that molten KOH will etch the plane of (101 ¯2)  and (101 ¯1 ¯ ) at 180°C. The etching will get more energy to do shrinkage, when we enhance the temperature to 260°C, and then the plane will change to (11 ¯00) and (101 ¯1 ¯ ). The H3PO4 will etch the plane of (11 ¯00) and (101 ¯1 ¯ ) at 180°C and 260°C. And then, the H3PO4+H2SO4 will etch the plane (101 ¯1 ¯ ) only at 180°C and 260°C.

致 謝 ...................................................................................................... IV
目錄 ....................................................................................................... VI
圖目錄 ................................................................................................... IX
表目錄 ................................................................................................ XIV
第一章 前言 ......................................................................................... 1
1-1 前言............................................................................................... 1
1-2 研究動機與目的 ........................................................................... 4
第二章 理論背景與文獻回顧 .............................................................. 6
2-1氮化鎵晶格排列 ............................................................................ 6
2-2氮化鎵蝕刻技術 ............................................................................ 9
2-3溼式蝕刻的技術發展 .................................................................. 11
2-4利用溼式蝕刻法製備表面粗化之技術 ....................................... 14
2-5 溼式蝕刻技術應用於氮化鎵磊晶層之研究 .............................. 18
第三章 實驗方法與步驟 .................................................................... 23
3-1 實驗藥品 ..................................................................................... 23
3-2 實驗儀器 ..................................................................................... 25
3-2.1 掃瞄式電子顯微鏡 ............................................................... 25
3-2.2 光激發螢光光譜 ................................................................... 27
3-3 實驗步驟 ..................................................................................... 28
第四章 實驗結果分析與討論 ............................................................ 30
4-1 氮化鎵薄膜面密度及表面能探討 .............................................. 31
4-2熔融態氫氧化鉀(Molten KOH)濕式蝕刻 ................................... 34
4-2.1 180oC氫氧化鉀對氮化鎵薄膜的蝕刻分析與討論 ............... 34
4-2.2 260oC氫氧化鉀對氮化鎵薄膜的蝕刻分析與討論 ............... 37
4-3 磷酸(86%)濕式蝕刻 ................................................................... 42
4-3.1 180oC磷酸(86%)對氮化鎵薄膜的蝕刻分析與討論 ............. 42
4-3.2 260oC磷酸(86%)對氮化鎵薄膜的蝕刻分析與討論 ............. 45
4-4 硫磷酸(3：1)濕式蝕刻 ............................................................... 49
4-4.1 180oC硫磷酸(3：1)對氮化鎵薄膜的蝕刻分析與討論 ......... 49
4-4.2 260oC硫磷酸(3：1)對氮化鎵薄膜的蝕刻分析與討論 ......... 52
4-5光激發螢光光譜之量測與探討 ................................................... 55
第五章 結論與未來展望 .................................................................... 59
5-1 結論............................................................................................. 59
5-2 未來展望 ..................................................................................... 60
參考文獻 ............................................................................................... 61

圖目錄
圖1-1 全球照明技術之市場趨勢情近推估 ........................................ 2
圖1-2 LED照明之應用.......................................................................... 3
圖1-3半導體材料之能隙發光光譜圖 ................................................... 3
圖2-1 HCP 單位晶格：(a)原子位置單位晶格；(b)硬球單位晶格；(c)隔離單位晶格 ....................................................................................... 6
圖2-2 氮化鎵Wurtzite結構排列 ........................................................ 7
圖2-3 氮化鎵之(a)晶體結構(b)單位晶胞 ........................................... 7
圖2-4 Wurtzite結構之晶格面定義 ...................................................... 8
圖2-5 氮化鎵磊晶層結構示意圖 (a) 鎵極性面 (b) 氮極性面 .......... 8
圖2-6 不同濕式蝕刻技術的裝置簡圖（a）一般的化學性濕式蝕刻 （b）電化學濕式蝕刻（c）光輔助電化學濕式蝕刻 ......................... 13
圖2-7 r-plane sapphire上側向磊晶成長a-plane GaN之橫切面圖 ..... 14
圖2-8 氫氧化鉀溶液，(a) 0.004 M，10分鐘之橫切面圖，(b) 為(a)之虛線框放大圖，(c) 0.55 M，10分鐘之橫切面圖，(d) 為(c)之虛線框放大圖 ............................................................................................. 15
圖2-9 磷酸溶液蝕刻，溫度120℃、時間5分鐘的俯視圖及其30度角圖 ..................................................................................................... 15
圖2-10 L-I-V量測不同（a）實驗及（b）模擬蝕刻結果的發光二極體之比較圖 ............................................................................................. 16
圖2-11 以KOH 與 H3PO4的溶液來進行交互性的選擇性濕式蝕刻之示意圖 ................................................................................................. 17
圖2-12 濕式蝕刻前後的PL峰值對波長的示意圖 .......................... 17
圖2-13 氫氧化鉀蝕刻c-plane氮化鎵之機制..................................... 19
圖2-14 氫氧化鉀蝕刻m-plane氮化鎵機制 ....................................... 20
圖2-15 氫氧化鉀蝕刻a-plane氮化鎵機制 ........................................ 21
圖3-1場發射掃描式電子顯微鏡之外觀 ........................................... 26
圖3-2 光激發螢光光譜量測系統 ...................................................... 27
圖3-4 實驗裝製圖 ............................................................................... 29
圖3-5 蝕刻樣貌隨時間改變結果示意圖 ............................................ 29
圖4-1 通過a面原子及各晶格常數示意圖 ........................................ 31
圖4-2氫氧化鉀，蝕刻溫度180oC，時間10分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 34
圖4-3氫氧化鉀，蝕刻溫度180oC，時間20分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 35
圖4-4氫氧化鉀，蝕刻溫度180oC，時間30分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 35
圖4-5氫氧化鉀，蝕刻溫度180oC，時間40分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 36
圖4-6氫氧化鉀，蝕刻溫度180oC，時間50分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 36
圖4-7氫氧化鉀，蝕刻溫度260℃，時間1分鐘。(a)為上方俯視圖，(b)為橫截面圖....................................................................................... 37
圖4-8氫氧化鉀，蝕刻溫度260℃，時間5分鐘。(a)為上方俯視圖，(b)為傾斜視角45度，(c)為橫截面圖 ................................................. 38
圖4-9氫氧化鉀，蝕刻溫度260℃，時間10分鐘。(a)為上方俯視圖，(b)、 (c)為橫截面圖 ............................................................................ 39
圖4-10根據蝕刻時間加長 面變化示意圖，(a) 為58.4o (b) 為62o .......................................................................................... 41
圖4-11 磷酸，蝕刻溫度180oC，時間10分鐘。(a)為上方俯視圖，(b)為橫截面圖 ........................................................................................... 42
圖4-12 磷酸，蝕刻溫度180oC，時間20分鐘。(a)為上方俯視圖，(b)為橫截面圖 ........................................................................................... 43
圖4-13 磷酸，蝕刻溫度180oC，時間30分鐘。(a)為上方俯視圖，(b)為橫截面圖 ........................................................................................... 43
圖4-14 磷酸，蝕刻溫度180oC，時間40分鐘。(a)為上方俯視圖，(b)為橫截面圖 ........................................................................................... 44
圖4-15 磷酸，蝕刻溫度180oC，時間50分鐘。(a)為上方俯視圖，(b)為橫截面圖 ........................................................................................... 44
圖4-16 磷酸，蝕刻溫度260oC，(a)、(b)為時間2分鐘之俯視圖及橫截面圖，(c)、(d) 為時間3分鐘之俯視圖及橫截面圖 ...................... 46
圖4-17 磷酸，蝕刻溫度260oC，(a)、(b)為時間4分鐘之俯視圖及橫截面圖，(c)、(d) 為時間5分鐘之俯視圖及橫截面圖 ...................... 47
圖4-18 磷酸，蝕刻溫度260oC，(a)、(b)為時間6分鐘之俯視圖及橫截面圖，(c)、(d) 為時間7分鐘之俯視圖及橫截面圖 ...................... 48
圖4-19硫磷酸，蝕刻溫度180oC，(a)、(b)為時間30分鐘之俯視圖及橫截面圖，(c)、(d) 為時間60分鐘之俯視圖及橫截面圖 ................ 50
圖4-20硫磷酸，蝕刻溫度180oC，(a)、(b)為時間90分鐘之俯視圖及橫截面圖，(c)、(d) 為時間120分鐘之俯視圖及橫截面圖 .............. 51
圖4-21 硫磷酸，蝕刻溫度260℃，時間30分鐘，(a)為俯視圖，(b)為傾斜視角45度圖 ............................................................................. 52
圖4-22 硫磷酸，蝕刻溫度260℃，時間45分鐘，(a)、(b)為之俯視圖及傾斜視角45度，(c)、(d) 為時間45分鐘之橫切面圖 .................. 53
圖4-23 硫磷酸，蝕刻溫度260℃，時間60分鐘，(a)、(b)為之俯視圖及傾斜視角45度圖，(c)、(d) 為橫切面圖 ....................................... 54
圖4-24 不同蝕刻溶液對氮化鎵濕式蝕刻之PL光譜圖 .................... 56
圖4-25 蝕刻孔洞PL量測之光子路徑圖，蝕刻溶液分別為，(a) 氫氧化鉀，(b) 磷酸，(c) 硫磷酸 ............................................................... 57

表目錄
表2-1 濕式蝕刻與乾式蝕刻的比較 .................................................... 10
表2-2 不同蝕刻溶液對氮化鎵材料之蝕刻率及蝕刻面表 ................. 11
表3-1 Hitachi S-4700I場發射掃瞄式電子顯微鏡重要規格 ............... 26
表4-1 氮化鎵各平面面密度整理表 .................................................... 33
表4-2 氮化鎵各平面蝕刻能障係數整理表 ........................................ 33

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