以矽化鎳基板成長石墨烯之研究

Abstract

石墨烯為碳原子以sp2鍵結所構成之六角蜂巢狀結構所組成的二維平面材料，由於其優異的電子性質以及機械性質，使得石墨烯在近年來引起許多研究團隊們的注意。為了將石墨烯應用於各式各樣的電子元件上，具備穩定且能生產出高品質石墨烯的製備方法是非常關鍵的因素。而在眾多製備石墨烯的方法當中，化學氣相沉積法為目前最主流的方式，但仍有些未解決的問題。首先其成長溫度動輒上千度，不利於與目前以矽為主體的半導體製程整合。其次則是目前的化學氣相沉積法需使用催化金屬基板例如銅或鎳，在應用上必須先將石墨烯由金屬基板轉印至介電基板如SiO2等。此轉印過程繁瑣並且容易造成石墨烯薄膜額外的損壞，更限制了大面積應用的可能性。 因此在本研究中，我們試圖以矽化鎳做為新的基板以成長石墨烯。矽化鎳做為半導體製程中的金屬接觸材料已有30年歷史，我們認為如果能於矽化鎳基板上成長出石墨烯，將可省去複雜的轉印步驟，並且加速石墨烯與目前半導體製程的整合。我們建設了超高真空化學氣相沉積系統，分別測試了化學氣相沈積法以及固態過飽和析出法兩種製程，我們利用穿透式電子顯微鏡(TEM)以及掃描式電子顯微鏡(SEM)觀察矽化鎳薄膜的晶體結構與表面形貌，並使用拉曼光譜儀分析矽化鎳基板表面是否有生成石墨烯與其品質。比較了三種矽化鎳結晶相Ni2Si、NiSi、NiSi2各自的催化能力之後，我們發現Ni2Si相具有最佳的催化能力。而將碳源從乙炔換成具多苯環結構的蒄能更加強碳sp2、sp3鍵結的生成。

Graphene is a two-dimensional crystal of carbon atoms packed in a honeycomb structure with the sp2 bonding, and it has been in the focus of intensive researches due to its unique physical properties. For almost ten years, the synthesis of large-area high-quality graphene has been an important issue, but there still remain some problems in the most routinely used chemical vapor deposition (CVD) process. First of all, the high growth temperature in the CVD method is unfavorable for integrating it with the current Si-based semiconductor technology. Secondly, even graphene can be grown on other metal substrates, the application of graphene still requires complicated transfer procedures, in which graphene is easily damaged and degraded. In this research, we propose to use various nickel silicide thin films on Si (111) wafer as the growth substrate, such as Ni2Si, NiSi and NiSi2. Since nickel silicides have been used as metal contacts in very-large-scale integration (VLSI) technology for more than 30 years, there is a great opportunity to integrate graphene into the technology. In this study, graphene growth is conducted in an ultra-high vacuum CVD (UHVCVD) system. The catalytic abilities of the three silicides are compared in two different growth methods, including the CVD and solid-phase precipitation method. We find that Ni2Si has the best catalytic ability. We also find that coronene with a polycyclic structure can further enhance the formation of C-C sp2 and sp3 bonding for the growth of carbon materials. In this work, we use transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to study the surface morphology and crystal quality of the nickel silicide substrates. We also use Raman spectroscopy to evaluate the quality of graphene.