【作者】 张进；

【导师】 冉均国；

【作者基本信息】 四川大学 ， 生物医学工程， 2005， 硕士

【摘要】 随着CVD金刚石质量及电学品质不断提高,高性能CVD金刚石电子器件的研制已成为该领域的热点研究课题之一。金刚石辐射探测器具有信噪比高、结构简单、可以在极端恶劣环境中正常工作等优点,而且金刚石的原子序数与人体软组织的原子序数非常接近,加之金刚石无毒,与组织液不会发生化学反应,是理想的生物活体内置辐射剂量探测材料。然而多晶金刚石薄膜的纯度和取向性对其电学、辐射响应性能有很大的影响,因此本文采用微波等离子体化学气相沉积（MWPCVD）装置,较全面研究了高纯、高[100]取向金刚石薄膜的制备工艺与电学和辐射响应性能之间的关系。 系统研究了反应气体中的CH₄浓度、基片温度、反应压力等工艺参数及三种不同的沉积工艺方法对金刚石薄膜生长及质量的影响。常规形核-生长金刚石薄膜的工艺方法纯度低,电阻率小;形核-刻蚀-生长工艺方法合成金刚石薄膜纯度提高,电阻率增大;形核-刻蚀-生长-刻蚀-生长……循环工艺方法合成金刚石薄膜纯度和电阻率>形核-刻蚀-生长工艺>常规形核-生长工艺,优化工艺制备出高纯、高[100]取向膜,其电阻率在10¹¹Ω.cm数量级,比常规工艺提高了3个数量级。 为了进一步提高金刚石薄膜纯度,除去表面的非金刚石成分,采用了简便的原位氧、氮、氢等离子体后处理技术对沉积出的金刚石薄膜进行后处理,电学测量结果表明后处理技术极大地提高薄膜的电阻率(最大达6个数量级,从～10⁸→～10¹⁴Ω.cm),有利于降低金刚石膜剂量计的漏电流,提高器件的信噪比,有利于提高辐射响应的灵敏度。更多还原

【Abstract】 With the improvement of the Chemical Vapor Deposition(CVD)diamond films properties including electrical characteristics, the fabrication of electronic devices based on the CVD diamond has been one of hot research subjects in this field. The diamond detector has many unique advantages, such as high signal-noise ratio, simple structure, normal output in extremely harsh surrounding and a tissue equivalent material. In addition, the diamond is non-toxic and inert to tissue fluid. Thus, the diamond is suitable for in - vivo radiation detection. The phase-purity and orientation of polycrystalline diamond films, however, have great effects on the electrical properties and the response to X-ray . In this paper, the relationship between the preparation processes of diamond films with high phase-purity and high-degree [100] preferential orientation and electrical properties and response to X-ray were studied systematically using a bell-jar type MWPCVD (microwave plasma assisted chemical vapor deposition) setup.The effect of growth parameters (methane concentration, substrate temperature, pressure) and different deposited techniques on the quality and the growth of diamond films were studied systematically. Using general nucleation-growth technique, the films with low purity and resistivity were deposited. With nucleation-etching-growth technique,the quality of the diamond films was somewhat improved. With nucleation-etching-growth-etching-growth cyclic deposition technique, the films with the highest purity and resistivity were deposited. Compared with the general technique, higher oriented [100]and higher resistivity (3. 9X10") diamond films can be deposited under the optimal cyclic deposition conditions .The resistivity of films can be increased by 3 orders of magnitude.A simple in-situ Oxygen Nitrogen> Hydrogen plasma etching post treatment method was used for the as-deposited films to improve their surface purity. Electrical measurements demonstrated that the resistivity is increased greatly up to 6 orders of magnitude (from 108 to 10HQ ? cm ). On the meantime, the leak current of radiation detectors was reduced and the signal to noise was improved. The sensitivity of radiation dosimeter was also increased.Dosimeters with simple Pt/Diamond film/Si sandwich structure were made and examined with steady - state X-ray source. The results show that the photocurrent output is proportional to the flux intensity of incident X-ray. But photocurrent signals became stable after 18 minutes due to the polycrystalline structure of the diamond films.The effect of the diamond films constitution and structure on the electrical properties and the response to X-ray was also studied. The results show that for the same orientation such as [100] or [111], the higher the resistivity of the film, the higher purity as well as the higher sensitivity. In addition, with the almost same resisvitity, the dosimeter based on [100] diamond film has higher sensitivity than that based on [111] diamond film .It is account for the better crystal structure, the less grain boundaries as well as the less defects of the [100] diamond film.The effect of preparation processes on the response to X-ray was studied. Purity and resistivity of the diamond films are different in different procedures. The dosimeter based on the films with cyclictechnique has the higher sensitivity than that with other deposition techniques.The effect of different plasma post-treatment methods on the response to X-ray was studied. The X-ray flux-photocurrent characterization also shows that in-situ plasma post-treatment can improve the diamond films sensitivity to X-ray irradiation. In-situ oxygen plasma processing led to better sensitivity of the dosimeters compared with in-situ nitrogen> hydrogen plasma processing .Because it can decrease more effectively the content of graphite and C-H bond in the as-grown films and improve the electrical properties of a new type dosimeter based on the diamond thin films.更多还原