臺灣博碩士論文加值系統

在現今積體電路設計強調元件縮小化的前提下，微影技術將會面臨許多發展瓶頸，以及在閘極長度 (gate length) 縮小至僅數十奈米的情形下，各種難以控制的物理現象也逐漸浮現。在這種由上而下 (Top-down) 的傳統縮小方式已無法突破極限的情況下，直接成長奈米結構的材料視為下一世代半導體技術的主要課題。例如：奈米碳管 (carbon nanotubes)、奈米線 (nanowires)，或是近年來相當熱門的單層石墨 (graphene) 等低維度 (Low-dimensional) 奈米結構，將這些奈米結構以積木 (block) 堆疊的組合方式構成電子元件，也就是所謂的由下而上 (Bottom-up) 建構技術，正是科學家積極研究發展的方向。單層石墨之所以能夠快速地在國際上掀起研究的熱潮，除了承續先前奈米碳管的研究能量之外，乃因為它是自然界中目前唯一能夠找到穩定存在的單一原子層二維電子系統，它獨特的電子結構給予科學界一個探索未知領域的重要平台，也提供奈米電子領域一個全新的思考方向。

目前製備單層石墨的方式最簡單的是利用機械剝離 (mechanical exfoliation) 的方式，但是這種方法不僅耗時，需要大量人力之外，由高定向熱解石墨 (HOPG) 剝離的石墨面積相對於現今業界晶圓尺寸大小的半導體製程難以帶到應用層面，因此本論文嘗試利用最常見的化學氣相沈積法 (Chemical vapor deposition, CVD)，來發展出簡單快速的單層石墨成長技術，並且逐漸改善問題，我們以鎳錠 (Ni pillar) 塊材做為催化劑以及現下最火紅的單層石墨成長金屬基材-銅分別成長單層石墨，為了更加瞭解石墨的成長機制，我們利用不同的分析儀器，像是拉曼光譜分析、掃瞄式電子顯微鏡、原子力顯微鏡等來幫助我們研究，且可以穩定地控制成長大面積的高品質且高均勻性單層石墨。

為了更加瞭解單層石墨元件的電學特性，在不同成長機制下，我們分析了單層石墨元件電學性質表現，像是電子遷移速率的比較，電荷中性迪拉克點的位置比較。對於基本的單層石墨電性有了基本的了解之後，我們則想要就由一些特殊的處理，讓本質的石墨有著類似於傳統以矽為基材摻雜效應 (doping effct)。配合著與發現奈米碳管的日本學者 Sumio. Iijima 的研發團隊合作的穿透式電子顯微鏡 (TEM) 技術，分析所量測的單層石墨，我們瞭解到以鎳為催化劑成長出的石墨烯其堆疊方式的獨特性質： AA 堆疊 (AA stacking)，以銅為金屬基板成長出晶格中低缺陷且只有一個原子層的單層石墨，再經過高溫爐管的退火去清除製程中無可避免的非晶碳、帶電與否的沉積物，並且修復單層石墨晶格成長過程中的缺陷等等，以及透過一系列的測試去增進接觸電阻 (contact resistance)，最後我們將看到其電學性質的改善。

在元件製作部分，鎳為基材的成長系統一般都是透過酸性溶液蝕刻催化劑，而銅為基材的成長系統則使用氯化鐵(FeCl$_{3}$)為蝕刻液，再用人力將石墨轉移至其他的基板上。由於將本實驗所成長出的單層石墨其顏色與轉移後的基板對比鮮明，利用光學影像即可非常容易地在 AutoCAD 定義其位置，這種製備單層石墨的方式穩定且可得到大面積、高品質跟均勻性的薄膜，不僅符合晶圓尺寸的需求，對於電學特性也優於傳統主流的矽。也就是說，此種有機材料若能克服目前在應用層面的問題，未來有機會能夠取代目前的矽，大量生產單層石墨元件，進而成為半導體科技的主流。

1. 緒論
1.1 低維度奈米結構的演進與發展
1.2 單層石墨的特色
1.2.1 單層石墨的電子能帶結構
1.2.2 單層石墨之電學特性
1.3 單層石墨在電子與光電元件上的應用

2. 單層石墨
2.1 石墨晶體結構
2.1.1 單層石墨
2.1.2 雙層與多層石墨
2.2 單層石墨的製備方法
2.2.1 機械剥離法
2.2.2 熱裂解磊晶成長於碳化矽上
2.2.3 氧化還原法
2.2.4 化學氣相沉積法
2.3 判斷單層石墨的工具
2.3.1 拉曼光譜儀
2.3.2 原子力顯微鏡
2.3.3 穿隧式電子顯微鏡

3. 單層石墨薄膜的製備
3.1 化學氣相沉積之介紹與製程參數
3.2 以過鍍金屬(鎳)為催化劑的化學氣相沉積成長
3.2.1 試片準備
3.2.2 薄膜成長參數
3.2.3 不同儀器之檢測結果
3.2 銅箔的化學氣相沉積成長
3.2.1 試片準備
3.2.2 薄膜成長參數
3.2.3 不同儀器之檢測結果

4. 元件製程
4.1 導論
4.2 實驗流程
4.3 單層石墨薄膜的轉移
4.4 電子束微影技術
4.5 反應式離子蝕刻技術
4.6 熱金屬蒸鍍
4.7 元件清潔
4.7.1 氧氣電漿
4.7.2 高溫退火
4.8 金屬導線連接與量測系統



5. 單層石墨電晶體與霍爾效應元件的電學性質
5.1 以鎳成長之單層石墨電晶體的電學性質量測
5.1.1 接觸電阻之改善
5.1.2 高溫退火對電性的影響
5.1.3 氨氣電漿對電性的影響
5.2 以銅成長之單層石墨電晶體的電學性質量測
5.3 實驗結果之比較與分析

6. 結論與未來展望

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