對於使用僅僅只有原子層厚度的過渡金屬硫族化物(Transition-metal dichalcogenides, TMDs)作為通道材料場效電晶體(Field-effect transistors, FETs)，金屬與半導體接觸工程一直是一個很重要的議題。傳統的金屬與TMDs接觸是利用微影製程的方式形成一個上端鍵結接觸(Top-bonded contact)的結構，會夾帶一個很大的蕭特基能障。為了要提供一個對載子注入更有效的方式，在論文中提出了末端鍵結接觸(End-bonded contact)的結構，能夠使通道材料的邊緣與接觸金屬有更強的共價鍵，利用預先鍍好的WO3-x/Pd/WO3-x晶種層(Seeding layer)與化學氣相沉積(Chemical vapor deposition, CVD)的方式來形成金屬-WSe2-金屬的末端接觸結構。如此一來單層的WSe2場效電晶體表現出卓越的特性，電流密度達到30 μA/μm、電動遷移率為90 cm2/V·s、次臨限擺幅為94 mV/dec，勝過同一通道材料的上接觸結構。另一方面也使用了密度泛函理論(Density function theory, DFT)對兩者結構進行模擬計算，結果指出末端接觸的Pd-W有更強的軌域混成以及富裕的禁帶能態，對於元件形成更佳的電性表現。

Contact engineering has been the central issue in the context of high-performance field-effect transistors (FETs) made of atomic thin transition metal dichalcogenides (TMDs). Conventional metal contacts on TMDs have been made on top via a lithography process, forming a top-bonded contact scheme with an appreciable contact barrier. To provide a more efficient pathway for charge injection, an end-bonded contact scheme has been proposed, in which covalent bonds are formed between the contact metal and channel edges. Yet, little efforts have been made to realize this contact configuration. Here, we bridge this gap and demonstrate end-contact WSe2 by means of chemical vapor deposition, in which the channel is grown from the two opposing WO3-x/Pd/WO3-x nucleation seeds, forming metal-WSe2-metal end contacts. Monolayer WSe2 FETs thus made exhibit remarkable performance metrics, including the on-current density of 30 μA/μm, hole mobility of 90 cm2/V·s, and subthreshold swing of 94 mV/dec, surpassing those of FETs sharing with the same channel but contacted on top. Calculations using density functional theory indicates that the superior device performance stems mainly from the stronger Pd-W hybridization and substantial gap states in the end contact configuration.

Abstract.........................................................I
論文摘要........................................................III
目錄............................................................ VI
第一章 緒論.......................................................1
1.1 半導體技術展. . . . . . . . . . . . . . . . . . . . . . . .. 1
1.2 傳統半導體的微縮與極限 . . . . . . . . . . . . . . . . . . . 2
1.3 二維層狀材料. . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 低微半導體的微縮與極限 . . . . . . . . . . . . . . . . . . . 5
1.5 論文結構 . . . . . . . . . . . . . . . . . . . . . . . . . . 10
第二章過 渡金屬二硫族化物介紹..................................... 11
2.1 過渡金屬二硫族化物之組合與晶型結構 . . . . . . . . . . . . . 11
2.2 過渡金屬二硫族化物之電子能帶結構 . . . . . . . . . . . . . . 14
2.3 過渡金屬二硫族化物材料製備方法 . . . . . . . . . . . . . . . 16
2.3.1 機械剝離法 (Mechanical exfoliation) . . . . . . . . . . .16
2.3.2 化學氣相沉積法 (Chemical vapor deposition) . . . . . . ...17
2.4 二硒化鎢材料檢測方式 . . . . . . . . . . . . . . . . . . . 20
2.4.1 拉曼散射頻譜 . . . . . . . . . . . . . . . . . . . . . .. 20
2.4.2 光致螢光光譜 . . . . . . . . . . . . . . . . . . . . . . 23
第三章 半導體材料與金屬接觸探討................................... 25
3.1 傳統塊材半導體之金屬接觸特性 . . . . . . . . . . . . . . . . 25
3.2 過渡金屬二硫族化物之金屬接觸特性 . . . . . . . . . . . . . . . 32
3.2.1 接觸金屬二硫族化物與費米能階釘札問題 . . . . . . . . . . . . 32
3.2.2 過渡金屬二硫族化物與金屬接觸機制 . . . . . . . . . . . . . . 37
3.2.3 改善接觸電阻之方法 . . . . . . . . . . . . . . . . . . . . 39
第四章 元件製作流程與材料檢測.................................... 47
4.1 末端金屬化接觸電極 . . . . . . . . . . . . . . . . . . . . . 47
4.2 二硒化鎢材料成長 . . . . . . . . . . . . . . . . . . . . . . 48
4.3 二硒化鎢材料檢測. . . . . . . . .. . . . . . . . . . . . . . 55
4.3.1 拉曼散射頻譜 . . . . . . . . . . . . . . . . . . . . . . . 55
4.3.2 光致螢光光譜 . . . . . . . . . . . . . . . . . . . . . . . 56
4.4 T型上閘極 . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.4.1 自然氧化閘極氧化層 . . . . . . . . . . . . . . . . . . . . 58
4.4.2 閘極結構與自我對準沉積 . . . . . . . . . . . . . . . . . . 59
4.5 離子液體上閘極 . . . . . . . . . . . . . . . . . . . . . . . 63
第五 章實驗量測結果與分析........................................ 67
5.1 接觸電阻分析. . . . . . . . . . . . . . . . . . . . . . . . 67
5.1.1 四點探針量測方法 . . . . . . . . . . . . . . . . . . . . . 67
5.1.2 二硒化鎢接觸電阻比較 . . . . . . . . . . . . . . . . . . . 68
5.2 鋁閘極電容量測. . . . . . . . . . . . . . . . . . . . . . . 71
5.3 元件結構介紹. . . . . . . . . . . . . . . . . . . . . . . 72
5.4 元件量測結果與分析. . . . . . . . . . . . . . . . . . . . . 74
5.5 互補式金氧半反相器 . . . . . . . . . . . . . . . . . . . . 79
第六章 實驗結果與未來展望...................................... 85
參考文獻...................................................... 87

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