在金剛烷披覆之矽基材上探討 鑽石的成核、成長與結構特性之研究

Abstract

鑽石薄膜有許多優良的特性，特別是在電子、光電、和光學應用上有極大的潛力。雖然鑽石合成技術已經達到了一個限度，在大面積商品化的需求下還存有一些不明且難以解決的問題，特別是在較低的溫度與壓力下進行鑽石薄膜的合成。因此，在本論文中，我們將會探討如何在較低的溫度(400~700°C)與壓力下進行鑽石薄膜的製備。 我們使用微波電漿化學氣相沉積法(MPCVD)進行成長，通入氫氣與甲烷的混合氣體作為反應用氣體，之後在披覆金剛烷(C10H16)的單晶矽基材上進行多晶鑽石薄膜的合成，並與在未披覆金剛烷的矽基材上所成長的鑽石薄膜進行比較。 結果我們發現在披覆金剛烷的單晶矽基材上所成長的鑽石薄膜其成長速率比未披覆金剛烷的快上兩倍。在單位面積中，其鑽石的分佈密度約為103 ~ 104 cm-2，也比未披覆金剛烷的分佈密度高。在中間的成長階段，我們觀察到金剛烷先轉變為與非晶碳相互混合的石墨相。隨後我們藉由X光繞射 (XRD) 與X光光電子光譜儀(XPS)進行鑽石薄膜的特性分析，證明了在鑽石沉積的過程中會形成碳化矽(SiC)界面層。同時我們使用原子力顯微鏡(AFM)與拉曼光譜儀(Raman)能得知在矽基材上有非鑽石相的存在。而此鑽石薄膜擁有優異的場發射性質：低臨界電壓(55 V/μm)與高電流密度(1.6 mA/cm2)。另外，在矽基材(SiO2/Si)上使用鉑顆粒能夠吸附金剛烷(碳氫化合物)並提升鑽石的成核密度高達1012 ~ 1013 cm-2；並且，矽基材表面上的氧化層能避免鉑和基材產生矽化反應，進而避免接下來鑽石的沉積過程中產生碳化矽。在一開始沉積的兩分鐘內，金剛烷的晶種轉變成奈米鑽石和一些未分辨的碳顆粒，並在之後5至15分鐘的沉積出現了石墨相。之後我們使用高倍率的掃描式電子顯微鏡(SEM)發現以{111}、{100}和許多方向性的碳顆粒成為鑽石成長的成核點。

Diamond films have been regarded as an active field of science and technology because of their unique properties. Although the technology of diamond film was synthesized to an extent, some problems remain unclear and only their solution can result in wide-scale commercialization, especially as the synthesis of diamond film at low temperature and pressure. Therefore, in the thesis, we will discuss the synthesis of diamond film at relative low temperature (400 ~700°C) and pressure. The polycrystalline crystalline diamond films were synthesized on adamantane (C10H16)-coated crystalline silicon substrates by microwave plasma chemical vapor deposition (MPCVD) from a gaseous mixture of methane and hydrogen gas without any mechanical and electrical pretreatments. Diamonds already grown on Si substrates without adamantane coating have been carried out as well as for comparison. As a result, we observed that the growth rate of diamond film on adamantane-coated Si substrates were two times faster than without adamantane-coated. The density of diamond on adamantane coated were also ~103~4 cm-2 higher than that of without adamantane coated. In the intermediate growth steps, we observed that the adamantane first converts into graphitic phase intermixed with amorphous carbon. The characterization of diamond films by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) show that the SiC interlayer have been formed during the diamond deposition. While atomic force microscope (AFM) and Raman spectra show the presence of nanodiamond phase on the Si substrate. The diamond films exhibit a low-threshold (55 V/μm) and high current density (1.6 mA/cm2) in their field-emission properties. In addition, using platinum particles on SiO2/Si substrates are adsorb adamantane (hydrocarbon) and increase the nucleation density ~1012~13 cm-2. The presence of oxide intermediate layer between Pt and Si prevents silicidation as well as SiC in diamond deposition. The seeded adamantane was first transformed into nanodiamond and some unidentified carbon particles in the early stage of deposition within 2 min while, further deposition (5-15 min) shows the existence of diamond and graphite phase. The high-magnification scanning electron microscope (SEM) have shown that the {111}, {100}, and many other orientated carbon particles may act as a nuclei for diamond growth.