利用微波電漿化學氣相沉積法於金矽液態基材上合成鑽石之研究

Abstract

摘 要 使用化學氣相沈積法在固態基材上合成鑽石已經有二十餘年的光景，然而在高品質的鑽石成長方面仍未有重大突破，鑽石在合成時直接影響鑽石品質的因素很多，包括電源功率、甲烷濃度、氣體流量、系統壓力、溫度及基材的表面型態等。就基材而言傳統上的選擇不外乎考慮晶格匹配性、基材缺陷、表面能及是否能與碳形成碳化物等因素，材料遍及了週期表內所能想像到的元素及化合物，然而效果並不顯著。因此，本論文研究重點著眼於基材，異於傳統上使用固態基材的方式，我們利用低溫化合物來形成液態基材在化學氣相系統下合成鑽石。 實驗選用金矽合金為基材，並控制其重量百分比約1比2，熔點約為700℃，於壓力20TORR真空腔體內，使用甲烷作碳源，氫電漿為解離甲烷的工具來合成鑽石，藉由改變偏壓大小、甲烷濃度、孕核方式、成長時間、圖案控制等參數，並使用XRD、RAMAN、TEM、SEM、EDS、ELLS等工具來分析鑽石品質及觀察鑽石在液態基材上成核及成長的機制。 實驗結果發現： 1.利用金矽液態基材來合成鑽石，可以得到品質不錯的鑽石。 2.在金矽液態基材上合成鑽石，鑽石的成核機制與在固態基材上合成鑽石有所不同，基材會形成類似鬚晶的單晶的矽，且朝311方向成長，然後鑽石會沉積在上面。 3.攏起的單晶矽與鑽石具有非常平整的界面，界面結構為氧化矽或碳化矽。 4.鑽石的尺寸與基材攏起物具有密切關係，攏起物直徑越粗則鑽石尺寸越大。 5.利用圖案的方式，同時在固態與液態的基材合成鑽石，鑽石會先在具有液態的地方成核並成長，顯示鑽石對液態基材與固態基材具有蠻高選擇比。 6.改變偏壓大小會對鑽石的成核密度造成影響，正偏壓越高成核密度用高。 7.改變成長濃度對成核密度沒有太大變化，對晶形的影響性較大，濃度越低晶形越好。

Abstract Chemical vapor deposition of diamond films on solid state substrates has been investigated for the past two decades, but the growth of high quality or highly oriented diamond film accepted by applications has not been achieved yet. Many parameters of growth process would affect directly the quality of diamond, such as methane concentration, gas flow rate, working pressure, substrate temperature, and surface conditions of substrate. The selection of substrate materials for diamond film deposition has to consider lattice structure, surface energy, carbon solubility of the substrates, or the affinity with carbon to form carbide phase. Furthermore, elements or compounds attempted to use as substrates for diamond deposition have covered all over the periodic table, but the effect on improvement quality of diamond is not notable. Thus, in this thesis, we used a low melting point alloy as substrate for chemical vapor deposition of diamond, which was very different to the conventional solid-state substrate. The liquid-state would exist at the temperature of chemical vapor deposition and to promote the synthesis of diamond. We used Au-Si alloy as substrate, which has the melting point about 700oC by using Au-Si weight ratio in 1:2. Diamond was synthesized by microwave assisted plasma chemical vapor deposition system, and hydrogen and methane was used as gas source. Then, we investigated the mechanism of the nucleation and growth of diamond synthesis on liquid state substrate under various bias voltage, methane concentration, and nucleation, growth duration, and patterned substrate by X-Ray Diffraction, Raman, Transmission Electron Microscopy, Scanning Electron Microcopy, Energy Dispersive Spectrometry, and Electron Energy Loss Spectrum analysis technology. In this study, we found: 1. The high quality diamond was obtained by using Au-Si liquid substrate. 2. The mechanism of diamond nucleation on liquid substrate was different on convention solid substrate. Substrate would form protrudent single crystal silicon, in cone shapel, and each protrudent single crystal silicon oriented along [311] crystallographic direction. Then, diamond was deposited on t top of the protrudent single crystal silicon. 3. The planar interface between diamond and silicon was observed, and silicon oxide and silicon carbide was existed at the interface. 4. The size of diamond depended on the size of the protrudent Si, and the thicker protrudent would form larger-size diamond. 5. When diamond deposited on the patterned substrates, diamond shows selective nucleation on the pattern where the liquid alloy had been formed, indicating that diamond nucleation have highly selective between liquid state and solid state substrate. 6. Varying bias voltages affects the diamond nucleation density. The higher nucleation density could be formed, by increasing bias positive voltage. 7. The variation on methane concentration was not found to affect the nucleation densities; however, the shape of diamond depends on the methane concentration. The methane concentration lower than 0.3﹪would result in well-faceted diamond.