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研究生:沈俊丞
研究生(外文):Chun-Cheng Shen
論文名稱:濕式蝕刻圖案化藍寶石基板表面處理對氮化鎵磊晶影響之研究
論文名稱(外文):Characterization of GaN Epitaxial Layers on Wet-etched Pattern Sapphire Substrates with Various Surface Treatments
指導教授:武東星
口試委員:洪瑞華林昆泉
口試日期:2011-01-31
學位類別:碩士
校院名稱:國立中興大學
系所名稱:精密工程學系所
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2011
畢業學年度:99
語文別:中文
論文頁數:81
中文關鍵詞:氮化鎵圖案化藍寶石基板表面處理結晶性載子遷移率
外文關鍵詞:GaN, patterned sapphire substratesurface treatmentcrystallinitymobility
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本論文將以乾式蝕刻對圖案化的藍寶石基板作表面處理,並探討以此基板所成長之氮化鎵薄膜的品質特性。本實驗採用的蝕刻氣體為四氟化碳,對藍寶石基板的蝕刻速率為180 A/min。當藍寶石基板用於成長氮化鎵薄膜時,由於兩種材料的晶格常數不匹配(晶格常數相差16 %),所成長的氮化鎵薄膜將產生許多缺陷,影響薄膜品質。這樣的結果使得載子輻射複合效率降低與產生大漏電流情況,為改善薄膜品質,論文中利用濕式蝕刻完成圖案化藍寶石基板的製作,再使用感應式耦合電漿蝕刻機台做表面處理,藉由乾式蝕刻對基板表面的粗糙度改變,以降低成長後的氮化鎵薄膜缺陷密度。
文章中分析比較乾式蝕刻做表面處理的前後氮化鎵薄膜性質。以高解析雙晶繞射儀、蝕刻孔洞密度法、光激發光光譜圖、掃描式電子顯微鏡與穿透式電子顯微鏡分析結果顯示,經過表面處理的圖案化藍寶石基板,其氮化鎵磊晶膜在高解析雙晶繞射對稱面(0002)面搖擺曲線半高寬降低17 %,非對稱面(10-12)面搖擺曲線半高寬降低12 %,載子遷移率由146 cm2/v-s增加至219 cm2/v-s,顯示薄膜品質有因此改善。

In this thesis, the characteristics of GaN epilayers grown on the wet-etched pattern sapphire substrates (PSSs) with various dry etching treatments have been investigated. The CF4 was used as the etching gas, achieving an etching rate of 180 A/min for the sapphire substrate. The PSS was treated using an inductively-couple-plasma etching system to modify the PSS surface morphology. It is well known that there exist high density defects in the GaN epilayer due to the large lattice mismatch between GaN and sapphire (~16 %). It will reduce the radiative recombination efficiency and cause large leakage current. Moreover, the treatment effects on the crystallinity and optical properties of GaN epilayers will be discussed.
We analyzed the results of GaN epilayer grown on wet-etched PSS with and without surface treatment. The GaN epilayer was measured by double-crystal x-ray diffractometry, etch pit density, photoluminescence, scanning electron microscopy, transmission electron microscopy, and van-der Hall measurement. The full widths at half maximum of both x-ray rocking curves in (0002) and (10-12) faces of the GaN epilayer on treated PSS were decreased by 17% and 12%, respectively as compared with those of the sample on untreated PSS. In addition, the electron mobility was increased by 50 % (from 146 cm2/v-s to 219 cm2/v-s). These results indicate that the improvement in epitaxial quality of GaN can be achieved on the PSS with a suitable post dry-etching treatment.

目錄
書名頁
審核頁
授權書
誌 謝 I
中文摘要 II
Abstract III
表目錄 VI
圖目錄 VII
第一章 緒論 1
1-1 前言 1
1-2 研究背景 2
1-3 研究動機 3
第二章 理論基礎與文獻回顧 7
2-1 藍寶石基板的結構性質 7
2-2 Ⅲ-Ⅴ族氮化物材料結構特性簡介 8
2-3 乾蝕刻原理及技術 9
2-4 藍寶石基板濕蝕刻技術與原理回顧 11
2-5 藍寶石基板與氮化鎵磊晶膜結構差異 13
2-6 貫穿式差排形成機制與影響 14
2-7 氮化鎵蝕刻孔穴與差排之關係 15
2-8 分析差排之方法 17
2-8-1 穿透式電子顯微鏡與差排之關係 17
2-8-2 X光搖擺曲線與差排密度之關係 17
第三章 實驗裝置、步驟與分析設備 30
3-1 實驗架構 30
3-2 實驗裝置 30
3-2-1 電漿輔助化學氣相沉積法 30
3-2-2 光罩曝光對準機 31
3-2-3 感應偶合電漿系統 31
3-3 實驗規劃與流程 31
3-3-1 製作圖案化藍寶石基板 31
3-3-2 圖案化藍寶石基板表面處理 32
3-3-3 成長無摻雜氮化鎵磊晶膜 33
3-4 分析設備 34
3-4-1 掃描式電子顯微鏡 34
3-4-2 穿透式電子顯微鏡 35
3-4-3 原子力顯微鏡 35
3-4-4 光激發光譜分析儀 36
3-4-5 X光繞射光譜儀 36
3-4-6 霍爾效應量測 37
第四章 實驗結果與討論 48
4-1 感應式耦合電漿蝕刻系統對藍寶石基板的蝕刻 48
4-2 氮化鎵磊晶膜初期成長 50
4-3 無摻雜氮化鎵磊晶膜表面缺陷分佈 51
4-4 無摻雜氮化鎵磊晶膜之光激發光特性分析 52
4-5 X光繞射法之差排密度 52
4-6 無摻雜氮化鎵磊晶膜之穿透式電子顯微鏡分析 53
4-7 室溫霍爾效應分析 53
第五章 結論與未來展望 74
第六章 參考文獻 76
表目錄
表2-1 藍寶石 (Al2O3) 常見的面代號與米勒指數 20
表2-2 藍寶石 (Al2O3) 的材料特性 20
表2-3 Ⅲ氮化物性質比較(W):Wurtzite (Z):Zincblende 20
表2-4 氮化鎵 (GaN) 材料特性 21
表2-5 乾/濕蝕刻對照表 21
表2-6 三種氮化鎵磊晶層中最常見的缺陷 22
表2-7 常用於分析差排之方法 22
表3-1 電漿輔助化學氣相沉積二氧化矽薄膜之沉積條件 38
表3-2 感應偶合電漿蝕刻二氧化矽薄膜之蝕刻條件 38
表3-3 感應偶合電漿表面微處理蝕刻條件 38
表4-1 氮化鎵磊晶膜各種缺陷在比例 54
表4-2 不同條件磊晶膜之XRD與載子遷移率 54
表4-3 基板經由CF4與Ar蝕刻效果 55

圖目錄
圖1-1 氮化鋁(AlN)、氮化鎵(GaN)、氮化銦(InN)能隙與晶格常數對應關係圖 5
圖1-2 濕蝕刻圖案化基板磊晶至全結構(a)表面不規則孔洞分佈之OM圖;(b)孔洞位於基板圖案附近之OM圖;(c)磊晶聚合不佳向上延伸之SEM剖面圖 6
圖2-1 六方晶結構示意圖 23
圖2-2 藍寶石(Al2O3)常見的面(a) c-plane俯視圖;(b)側視圖[15] 24
圖2-3 藍寶石(Al2O3)的材料特性 25
圖2-4 乾、濕式蝕刻反應 25
圖2-5 濕式蝕刻反應過程示意圖 26
圖2-6 異質磊晶結構晶格不匹配現象之橫截面示意圖 26
圖2-7 差排示意圖(a)刃差排;(b)螺旋差排 27
圖2-8 氮化鎵二極體結構內部之差排型態示意圖 27
圖2-9 (a)氮化鎵磊晶膜表面被蝕刻後之SEM圖;(b)氮化鎵磊晶膜表面被蝕刻後之AFM圖;(c) α、β、γ三種蝕刻孔洞之側向形貌示意圖;(d) α蝕刻孔洞之TEM剖面圖;(e) β蝕刻孔洞之TEM剖面圖 28
圖2-10 差排分佈於GaN/sapphire之TEM剖面圖 29
圖3-1 實驗流程圖 39
圖3-2 PECVD系統結構示意圖 39
圖3-3 感應式耦合電漿系統 40
圖3-4 濕式蝕刻圖案化藍寶石基板製作流程圖 41
圖3-5 濕式蝕刻圖案化藍寶石基板之SEM俯視圖 42
圖3-6 單顆濕式蝕刻圖案化藍寶石基板之SEM俯視圖 42
圖3-7 第一層氮化鎵磊晶膜製程溫度與時間關係圖 43
圖3-8 第二層氮化鎵磊晶膜製程溫度與時間關係圖 43
圖3-9 掃描式電子顯微鏡 44
圖3-10 原子力顯微鏡量測系統圖 44
圖3-11 光激發光光譜量測系統示意圖 45
圖3-12 光激發光輻射再復合過程示意圖 45
圖3-13 X光繞射量測系統圖 46
圖3-14 霍爾效應量測系統 47
圖4-1 CF4對藍寶石基板乾蝕刻(a)上電極輸出功率250 ~ 1000 W;(b)下電極輸出功率50 ~ 200 W;(c)腔體壓力5 ~ 20 mTorr之蝕刻率變化 57
圖4-2 CF4乾式蝕刻於上電極輸出功率500 W、腔體壓力10 mTorr、時間10 mins,不同下電極輸出功率(a) 50 W;(b) 100 W;(c) 200 W條件下作表面處理後濕蝕刻圖案化基板形貌變化之SEM俯視圖 59
圖4-3 以下電極200 W - CF4乾蝕刻表面處理後,單顆基板圖案之SEM圖 60
圖4-4 氮化鎵磊晶膜成長在表面處理後之濕蝕刻圖案化基板,磊晶膜表面破損情況之倍率500倍的OM圖 60
圖4-5 以倍率1000倍的OM觀察破損區域之氮化鎵磊晶膜(a)對焦於磊晶膜表面;(b)對焦於下方基板圖案 61
圖4-6 CF4乾式蝕刻於上電極輸出功率500 W、下電極輸出功率50 W、腔體壓力10 mTorr (a) 5分鐘;(b) 10分鐘分別作表面處理後濕蝕刻圖案化基板形貌變化之SEM俯視圖 62
圖4-6 500-50 W (a) 5 mins;(b) 10 mins之SEM圖 62
圖4-7 CF4乾式蝕刻於上電極輸出功率500 W、下電極輸出功率50 W、腔體壓力10 mTorr (a) 5分鐘;(b) 10分鐘分別作表面處理後濕蝕刻圖案化基板形貌變化之SEM圖 63
圖4-8 原子力顯微鏡掃描基板粗糙度變化 64
圖4-9 完整無破損之氮化鎵磊晶膜成長於5分鐘與10分鐘表面處理之濕蝕刻圖案化基板,倍率500倍的OM圖 65
圖4-10 無摻雜氮化鎵磊晶膜初期成長於未處理之濕蝕刻圖案化基板SEM俯視圖 65
圖4-11 無摻雜氮化鎵磊晶膜成長於未處理之濕蝕刻圖案化基板SEM剖面圖 66
圖4-12 無摻雜氮化鎵磊晶膜初期成長於經乾蝕刻表面處理基板之SEM俯視圖 66
圖4-13 沒有空孔殘留的無摻雜氮化鎵磊晶膜成長於經乾蝕刻表面處理圖案化基板之SEM剖面圖 67
圖4-14 無摻雜氮化鎵磊晶膜成長於(a)未處理圖案化基板;(b)經表面處理之圖案化基板演進示意圖 68
圖4-15 無摻雜氮化鎵磊晶膜缺陷密度分佈SEM圖(a)未處理之圖案化基板;(b)表面處理5分鐘之圖案化基板;(c)表面處理10分鐘之圖案化基板 70
圖4-16 光激發光譜圖分析於不同基板成長無摻雜氮化鎵磊晶膜之品質 70
圖4-17 不同基板成長無摻雜氮化鎵磊晶膜之(0002) XRD rocking curve圖 71
圖4-18 不同基板成長氮化鎵磊晶膜之(10-12) XRD rocking curve圖 71
圖4-19 (a);(b)無摻雜氮化鎵磊晶膜成長於未處理圖案化基板之TEM剖面圖 72
圖4-20 無摻雜氮化鎵磊晶膜成長於經表面處理圖案化基板之TEM剖面圖,於圖案頂部產生差排線彎曲 73


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