Research On The Boron-doping Process Of Nanocrystalline Diamond Thin Films

On the basis of excellent performance of traditional diamond films, nano-crystalline diamond film introduce a new feature because of its gain size. It’s an improvement for solving some limitations in micro-crystalline diamond film common application and application area extensions of diamond films. In order to optimize the process for preparing nano-crystalline diamond films with smooth surface and fine gain size, influence of reaction pressure, microwave power, carbon concentration and deposition time on nano-crystalline diamond films has been discussed on the basis of existed theory and experiments of laboratory, which synthesized by MPCVD method.It was found that: the mean free path of reactive groups in plasma would increase with the decreasing reaction pressure. It means that reactive groups can devote more energy to growth interface during the colliding process, as the reduction of energy during motion process. By this way, the activity of the adsorbed particles was enhanced and carbon clusters formed on the substrate surface more rapidly. And then the diamond nucleation rate and the secondary nucleation rate are improved. It’s more conducive to the growth of nano-crystalline diamond films with smooth surface. C2 content in the plasma would increase as the microwave power increase. More carbon-containing groups in plasma will generate at high power,which also mean that the presence of high-speed growth area of nano-diamond films with good quality under the condition of higher power. And it is difficult to completely cover the substrate scratches if the deposition time is too short, on the converse, the grain growth pattern will gradually change to columnar growth pattern and will form micron-sized diamond grains if the deposition time is too long.High carbon group concentrations can be obtained by high CH4 concentration. Therefore, the relative concentration of H atoms can be reduced,resulting in the deduction of the etching rate of non diamond phase. As a result, the nucleation rate and the secondary nucleation rate is improved and nano-crystalline diamond films with smaller grain size and surface roughness can be deposited.The most suitable Process parameters for preparing the nano-crystalline diamond film by 10kW-MPCVD apparatus have been achieved. It is respectively the microwave power of 3.5kW, the deposition time of 4-6h, the reaction pressure of 2.5kPa, and 6% of the carbon source concentration. Under this condition, nano-crystalline diamond films were prepared with the crystalline size is about 30 nm, the surface roughness of 20 nm or less.In order to promote the application of nano-crystalline diamond films in the semiconductor and other electrical field. Research of doping borane on NCD films has be carried out using MPCVD method. Systematic discussion and doping mechanism analysis have be carried on to find suitable parameters for introducing well electrical properties into nano-crystalline diamond films. There are some influencing factors in the investigation summarily of the boron-doped nano-diamond films, namely microwave power,reaction pressure,substrate temperature,doping time and the concentration of boron in reaction gas.The experimental results show that the grain size and surface roughness of the nanodiamond films will increased significantly from about 55 nm to 80 nm within the substrate temperature enhanced from 600℃ to 750℃.The concentration of boron-doped and doping time have the same influence to the surface morphology.Meanwhile, with the increase of substrate temperature in the process of doping, the surface resistivity of the doped films will reduce. The downtrend is particular significant at the temperature range from 750 ℃to 850℃.The influence of doping concentration to the surface properties of the films is similar to substrate temperature. And the surface resistivity will reach a saturation value along with the increase of the doping concentration. This saturation value is generally within the range of 250~200??□. Moreover,with the increasing of doping time,the surface resistance will rapid decrease firstly and then remain unchanged.