The Study of Growth of Oriented Diamond Films by Bias Method
|關鍵字:||鑽石薄膜;矽鍺;鍺;穿透式電子顯微鏡;異質磊晶;diamond film;silicon germanium;germanium;transmission electron microscope;heteroepitaxy|
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.