CO_2-CH_4沉积气氛中金刚石膜晶粒尺寸的控制研究

Investigation on the Grain Size Control of Diamond Films in CO_2-CH_4 Gas Mixture

目的在无氢气沉积环境中研究CO_2与CH_4的流量比对金刚石膜生长及晶粒尺寸的影响规律。方法采用MPCVD技术,通过调控CO_2与CH_4的流量比,可控性地制备得到不同结构特征的金刚石膜,通过SEM、XRD以及Raman光谱对金刚石膜进行表征分析,获得CO_2与CH_4的流量比对金刚石膜晶粒尺寸的影响规律。结果在微波功率、沉积气压、基片温度和CH_4流量分别为1.2 k W、7.0 k Pa、850℃和50 mL/min的沉积环境下,当CO_2流量为20和25 mL/min时,可制备得到纳米金刚石膜;当CO_2流量为30和35 mL/min时,可制备得到微米金刚石膜;当CO_2流量为67 mL/min时,可获得金刚石颗粒。在保持其他工艺条件不变时,通过调控微波功率分别为0.9、1.4和1.8 k W,金刚石膜的晶粒尺寸随CO_2/CH_4的变化可分为:纳米金刚石膜区(CO_2/CH_4<50%)、微米金刚石膜区(CO_2/CH_4>60%)及纳米-微米过渡区(50%<CO_2/CH_4<60%)。结论降低CO_2与CH_4流量比,有利于减小晶粒尺寸。

The work aims to study law of influence of CO2/CH4 flow ratio on growth of diamond films and grain size. The diamond films exhibiting different structural features were prepared controllably by adjusting the CO2/CH4 flow ratio and applying MPCVD technology. The diamond films were characterized and analyzed with scanning electron microscope, X-ray diffractometer and Raman spectrum, the rule of influence of CO2/CH4 flow ratio on grain size of diamond films was obtained. When microwave power, deposition pressure, substrate temperature and of CH4 flow was 1.2 kW, 7.0 kPa, 850 ℃ and 50mL/min, respectively, nanocrystalline diamond films could be deposited using 20 and 25 mL/min CO2, microcrystalline diamond films could be obtained using 30 and 35 mL/min CO2, and diamond could be deposited using 67 mL/min CO2. By adjusting mi- crowave power to 0.9, 1.4, 1.8 kW, respectively while keeping the other parameters constant, grain size variation of diamond films along with the CO2/CH4 flow ratio could be divide into three regions： nanocrystalline diamond film deposition region （CO2/CH4〈50%）, microcrystalline diamond film deposition region （CO2/CH4〉60%）, and grain size transition region （50%〈C02/CH4〈60%）. It is feasible to conclude that the decrease of C02/CH4 flow ratio is conductive to decreasing grain size of diamond films.