偏壓法生長方向性鑽石薄膜之研究

Abstract

本實驗利用偏壓輔助孕核微波電漿化學氣相沉積法，於矽、鍺及矽鍺基材上合成鑽石，探討偏壓法生長方向性鑽石薄膜之研究。我們依偏壓輔助孕核的形式及基材種類的不同將論文分為三個主題來加以探討。第一個主題是探討鑽石在矽鍺基材上的成長。鑽石在矽基材上面的成長已有相當多的研究，但對於矽鍺基材則幾乎沒有相關的文獻可供參考。在這個主題中，我們用超高真空鍍膜機所沉積的矽鍺薄膜做為基材，進行鑽石沉積，所得到的結果利用掃描式電子顯微鏡、Raman光譜儀及穿透式電子顯微鏡進行分析。由分析的結果可以得知鑽石於矽鍺基材上的成核密度高於109cm-2，而且一樣可以得到高方向性的(100)鑽石薄膜，而鑽石與基材界面可同時觀察到鑽石直接生長在SiGe基材上及□碳化矽的形成。第二個主題則是探討鑽石在鍺基材上的成長，鍺的溶碳率低，且不易與碳形成碳化物，使用鍺做為基材是期望能利用基材的特性，輔助鑽石在基材上的成核狀況。在利用各種不同條件進行鑽石的成長度可發現，在未加偏壓的情況下，鑽石在鍺基材上的成核密度約108cm-2左右，比矽及矽鍺基材高出約3個order左右，且鑽石的晶形呈現出(111) 的織構。利用Raman光譜儀的分析，可發現鑽石的品質相當好，而透過穿透式電子顯微鏡的分析，則會發現鑽石與鍺基材存在有(111)鑽石||(100)鍺的方位關係，且於其界面中存在一層石墨層。鑽石與鍺基材的接著性極差，經過120分鐘的生長後，會形成連續性的鑽石薄膜，但極容易剝落，這應該與其膨脹系數差異太大及石墨界面層的存在有著相當大的關係。最後一個主題則是要討論正偏壓法對鑽石生長的影響。此實驗於矽基材上施加正偏壓進行鑽石輔助孕核，結果發現正偏壓法可成功地提高鑽石的成核密度至1×109cm-2以上。於成核後利用選擇方向性鑽石成長的方式，可同時得到(100)及(111)方向性鑽石薄膜。藉由XRD的分析結果可發現在長時間生長後(111)及(100)鑽石的比例有顯著的增加。利用穿透式電子顯微鏡及電子損失能譜儀的分析，可發現基材表面相當平整，且在鑽石與矽基材的界面間存在一非晶質碳。

Diamond films were synthesized on Si, Ge and SixGe1-x substrates by bias-enhanced nucleation in microwave plasma chemical vapor deposition. In this work, we have studied growth of oriented diamond films on various substrates by bias method. The dissertation is divided into three parts which show the effects of various bias method and substrates on diamond nucleation and growth. In first part of the dissertation, we focus on the growth of diamond on SiGe substrate. Diamond growth on Si substrates has been studied intensively, however, the study of diamond growth on SiGe substrate is rare. In this part, on SiGe thin films for diamond growth were deposited by ultra high vacuum chemical vapor deposition. Scanning electron microscopy, Raman spectroscopy and transmission electron microscopy were used to characterize the nucleation density, morphology, quality of diamond, and the interface between diamond and substrate. The results show that the nucleation density of diamond is higher than 109cm-2, and (100) oriented diamond films can be achieved on SiGe substrates. Diamond can either directly grow on SiGe substrates, or on □-SiC interlayer. The second part of the dissertation, diamond growth on germanium substrate is studied. The solubility of carbon in germanium is very low, and germanium with carbon was hardly to form a carbide. The purpose of using germanium as the substrate is to enhance the nucleation density of diamonds. By using various parameters to deposit diamond on germanium, it was observed that the nucleation density of diamond grains can be achieved to 108cm-2 without a bias applied, which was almost 3 orders higher than that on Si. The (111) textured diamond grains were observed. Raman spectrum results have shown the quality of diamond is good. Through the analysis of transmission electron microscopy, the orientation relationship, (111) diamond || (100) Ge , can be observed, and a graphite interlayer was also observed between diamond and germanium. After 120 minutes growth of diamond, a continuous diamond film was formed on germanium substrate, however, the film was easily peeled off from the substrate because of the poor adhesion between diamond and germanium. It could be resulted from the existence of graphite layer and the large difference in thermal expansion coefficients between diamond and germanium. The last part of the dissertation, the influence of diamond growth by positive bias method was discussed. The positive bias was applied to Si substrates, and a nucleation density is higher than 109cm-2 was achieved. The X-ray diffraction results shown that the ratio of (111) and (100) diamond grains were increased after long period growth, and oriented (111) and (100) diamonds can be achieved on Si (111) and Si (100) substrate, respectively. Observation from transmission electron microscope images and electron energy loss spectrum, the silicon surface is smooth, and an amorphous interlayer exists between diamond and Si.