二次形核率对金刚石膜生长的研究

发布时间：2018-07-12 08:00

  本文选题：微波等离子体 + 化学气相沉积　； 参考：《武汉工程大学》2016年硕士论文

【摘要】：随着气相沉积技术的发展,CVD金刚石已经具备与天然金刚石相差无几的优异特性,在诸多技术领域拥有非常好的实际应用前景。微波等离子体化学沉积方法具有无极放电、对沉积环境不产生污染的特点,是制备微米、纳米及超纳米金刚石膜最为理想的方法之一。目前,国内外研究学者将主要目光集中在如何进行金刚石膜的可控性生长方面,通过添加惰性气体、控制甲烷浓度等方式进行相关研究,其根本目的在于控制薄膜制备过程中的内在反应机制。二次形核作为金刚石膜生长过程中重要阶段之一,其速率的高低对金刚石膜的生长速率、表面形貌、晶粒尺寸及薄膜质量方面有不同程度的影响。因此研究如何控制二次形核现象,探究二次形核率的高低对于薄膜生长的影响具有重要意义。本研究利用韩国Woosinent公司R2.0-MPCVD设备及实验室自制的石英钟罩式MPCVD设备,分别讨论了在惰性气体(Ar)添加及典型气氛条件(CH4/H2混合气体)下如何控制薄膜生长过程中的二次形核现象,并分析了二次形核率的高低对于金刚石膜晶粒尺寸、质量及晶面取向的影响。主要研究工作如下:在利用CH4/H2/Ar为气氛环境生长金刚石膜时,当氩气流量低于一定阀值(92.5sccm),制备得到的样品表面形貌成为微米结构。在氩气流量由80.0sccm向92.5sccm增加的过程中,微米级晶粒晶界处出现少量由二次形核现象产生二次晶核。惰性气体Ar的添加对控制二次形核现象有一定影响:当Ar流量增加到95.0sccm以上时,二次形核现象得到促进,晶界处晶核增加,抑制了初始晶粒的长大,晶粒尺寸急剧下降。当Ar流量为95.0sccm时,薄膜表面逐渐呈现团聚体构成的纳米金刚石形貌;特别是当Ar流量增加至97.5sccm时,薄膜呈现出由二次形核长大的晶粒构成的“针状”的超纳米级金刚石形貌。在高Ar流量条件下(95.0sccm)沉积金刚石膜,由于等离子体中H原子含量所占的比例较小,对沉积过程中的非金刚石相刻蚀效果变差,使得最终沉积的样品中金刚石相相对含量降低,非晶碳和石墨含量增加。同时薄膜表面主要显现(111)晶面。在利用CH4/H2典型气氛环境条件生长金刚石膜时,在增加CH4浓度的过程中,金刚石结构和特性出现明显改变。当CH4浓度由1.0%增加到2.5%时,因CHx基团浓度增加而堆积的二次晶粒增多,促进了二次形核现象,从而引起金刚石膜晶粒尺寸急剧下降,同时膜层中非金刚石相含量随之增加,薄膜质量明显变差。当CH4浓度≤1.5%时,金刚石晶面取向以(111)面和(220)面为主,其中(111)面强度远远高于(220)面;CH4浓度≥2.0%时,从XRD图可以看到,金刚石膜晶面主要以(111)面为主,虽然部分金刚石显露为(220)和(311)晶面,但薄膜整体呈现(111)取向,这说明CH4浓度的增加引起的二次形核对金刚石的晶面取向影响不大。
[Abstract]:With the development of vapor deposition technology CVD diamond has the same excellent characteristics as natural diamond and has a very good application prospect in many technical fields. Microwave plasma chemical deposition is one of the most ideal methods for the preparation of micron nanocrystalline and ultrananocrystalline diamond films due to the characteristics of electrodeless discharge and no pollution to the deposition environment. At present, researchers at home and abroad are focusing on how to control the growth of diamond films, by adding inert gas, controlling methane concentration and other ways. Its fundamental aim is to control the internal reaction mechanism in the preparation of thin films. Quadric nucleation is one of the most important stages in the growth of diamond films. The growth rate, surface morphology, grain size and film quality of diamond films are affected by the rate of growth. Therefore, it is of great significance to study how to control the phenomenon of quadratic nucleation and to explore the influence of the rate of quadratic nucleation on the growth of thin films. In this paper, using the R2.0-MPCVD equipment of Woosinent Company of Korea and the quartz bell type MPCVD equipment made by our laboratory, we discussed how to control the quadratic nucleation in the process of thin film growth under the conditions of (Ar) addition and typical atmosphere (CH4 / H2 mixed gas), respectively. The influence of the secondary nucleation rate on the grain size, quality and orientation of diamond films was analyzed. The main research work is as follows: when the diamond film is grown in the atmosphere of Ch _ 4 / H _ 2 / ar, the surface morphology of the sample becomes micron when the argon flow rate is lower than a certain threshold (92.5sccm). In the process of argon flow rate increasing from 80.0sccm to 92.5sccm, a small amount of secondary nucleation occurs at the grain boundary of micron grain. The addition of ar has a certain influence on the control of quadratic nucleation: when ar flow rate is higher than 95.0sccm, the secondary nucleation is promoted, the nucleation at grain boundary increases, the initial grain growth is restrained, and the grain size decreases sharply. When ar flow rate is 95.0sccm, the surface of the film gradually presents the morphology of nano-diamond composed of agglomerates, especially when ar flow rate is increased to 97.5sccm, the film presents a "needle-like" ultrananocrystalline diamond morphology composed of grains grown by secondary nucleation. Under the condition of high ar flow rate (95.0sccm), due to the small proportion of H atom in the plasma, the etching effect of the non-diamond phase in the deposition process is poor, which results in the decrease of the relative content of diamond phase in the final deposited sample. The content of amorphous carbon and graphite increased. At the same time, the surface of the film is mainly (111) crystal surface. When diamond films were grown under the typical atmosphere of Ch _ 4 / H _ 2, the structure and properties of diamond films changed obviously when the concentration of Ch _ 4 was increased. When the concentration of Ch _ 4 increased from 1.0% to 2.5%, the secondary grains accumulated with the increase of Ch _ x group concentration increased, which promoted the phenomenon of secondary nucleation, which led to the sharp decrease of grain size of diamond film and the increase of the content of non-diamond phase in the film layer. The quality of the film becomes worse obviously. When the concentration of Ch _ 4 鈮，

本文编号：2116502