【作者】 庞博；

【导师】 于杰；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2016， 硕士

【摘要】 金刚石在自然界已知的材料中硬度、密度、声速、导热率和弹性模量,都是最高的。同时,金刚石还具有极低的热膨胀系数、极宽的带隙宽度以及良好可见光透射率。在高温下金刚石也不与普通的酸性物质发生化学反应,有良好的化学稳定性。金刚石众多的突出性质使得它在刀具、导热、窗口材料、大功率器件、微波器件等方面具有重要的应用价值,但高透明金刚石薄膜及外延单晶生长仍然存在很多问题需要解决。本文利用微波等离子体化学气相沉积法(MPCVD)合成金刚石。主要工作分为两部分,一是以高温高压合成的金刚石为籽晶,在其表面上同质外延生长出高透明度的金刚石单晶;二是在钼衬底上生长金刚石薄膜,通过调节参数获得高透明度的自支撑金刚石薄膜。金刚石单晶外延主要研究在较低温度下,不同的气体流量对单晶生长的影响。首先以CH4和H2为气源,分别研究功率、气压、温度对单晶金刚石生长的影响,得到优化的工艺参数。研究表明,在一定参数范围内单晶的生长速率随着功率、气压、温度的升高而升高。研究发现温度是影响单晶质量的重要因素,温度越低单晶质量越好,所以在低温条件下研究气体流量对单晶生长的影响。单晶的生长速率随着甲烷流量的升高而升高,流量过高时单晶金刚石发生石墨化。氧气可以有效刻蚀非金刚石相,在反应气源中加入氧气,单晶的生长速率随着氧气流量的升高而降低,且流量在0.1-0.5 sccm区间,流量越高单晶质量越好。按比例同时增加甲烷和氧气的流量,可使甲烷流量过高时石墨化的籽晶继续生长单晶金刚石。金刚石薄膜主要研究了温度、功率、氧气流量对其生长的影响。自支撑金刚石薄膜的生长速率随着温度、功率的升高而升高,随着氧气流量的升高而降低。在一定范围内,薄膜的可见光透射率随着温度的升高先增加后降低,随着功率、氧气流量的增加而增加。氧气流量1.0 sccm时薄膜的可见光透射率最高。更多还原

【Abstract】 Diamond has the highest hardness, atomic density, sound velocity, thermal conductivity, and elasticity modulus among the known naturally existing materials. In addition, diamond also has very low thermal expansion coefficient, extremely wide band gap, and good visible light transmittance. Diamond has high chemical stability and does not react with common acid even at high temperature. Due to the numerous advantages diamond has important applications for cutting tools, thermal conduction, optical windows, high-power devices, microwave devices, and so on. However, the growth of high transparency free-standing diamond films and epitaxial single crystals growth is still a problem in China.In this thesis, growth of high transparency diamond films and single crystals was investigated by microwave plasma chemical vapor deposition(MPCVD). The research work includes two parts. The first is epitaxial growth of high transparency diamond single crystals on diamond seeds prepared by high temperature and high pressure technology. The second is deposition of highly transparent free-standing diamond films on molybdenum substrates.At low temperature, the effects of the gas flow rate of the different gases on the epitaxial growth of diamond single crystals was investigated. CH4 and H2 were used as the reactive gases during the experiments and the effects of the power, working pressure, and temperature on the growth of the single crystal diamond were investigated, obtaining the optimal process parameters. In a certain range, epitaxial growth rate increases with increasing the power, working pressure, and temperature. It is found that the temperature is an important factor affecting the quality of diamond single crystals and the higher quality was achieved at lower temperature. Therefore, the effect of the gas flow rate was investigated at low temperature. The epitaxial growth rate increases with increasing the methane flow rate. However, too high temperature results in graphitization of the diamond. Oxygen was added during the epitaxial growth of the diamond single crystals due to its etching reactivity on non-diamond phase. It was found that in the oxygen flow rate range from 0.1 to 0.5 sccm the quality of the epitaxial diamond increases with increasing the oxygen flow rate. However, the growth rate decreases correspondingly. Increasing the flow rates of methane and oxygen sychronously with their ratio constant results in the graphitization of the diamond continue to grow single crystal finally.The growth of the highly transparent free-standing diamond films was investigated as a function of temperature, power, and oxygen flow rate. The growth rate increase with the increase of temperature and power, decrease with the increase of oxygen flow rate. In a certain range, the visible light transmittance increase with the increase of oxygen flow rate and power. The visible light transmittance increase with the increase of temperature first and then decrease. When the oxygen flow rate is 1.0 sccm, diamond films has the highest transmittance.更多还原