Study On High Rate Growth Of Diamond Film By Microwave Plasma Chemical Vapor Deposition

Diamond is the hardest material in the world, and also has very low thermal expansion coefficient, high thermal conductivity, wide band gap, good light transmittance, and other excellent performances. It is very suitable for optical window and the protective film of optical lenses, and also can be used for high power laser devices, microwave devices, and integrated circuits. Although a lot of research has been conducted, the growth rate of diamond film is not so high due to the limitation of the domestic technology, which restricts its practical application.In this thesis, diamond films have prepared using microwave plasma chemical vapor deposition(MPCVD) method with CH4 and H2 as gas sources. Influences of the process parameters on the growth rate and quality of the diamond films are studied. We also use Raman spectroscopy, Scanning electron microscopy, and X-ray diffraction to characterize the diamond films. The specific work is as follows:We studied the influence of CH4 concentration and H2 flow rate on the diamond films, and grew diamond films with high quality and high growth rate by controlling the CH4 concentration and H2 flow. With the increase of CH4 concentration the growth rate of diamond film increases first and then keep stable after increasing the concentration over 2.5%. Too high or too low hydrogen flow rate will result in the decrease of the growth rate and the highest growth rate is at 200 sccm. It is proved that CH4 concentration and H2 flow rate play important roles in the film growth.Diamond films with high quality and high growth rate have grown by controlling the temperature and microwave power. The growth temperature is dependant on the microwave power. With the increase of microwave power the growth temperature increases, and the plasma size will increase. The plasma can be completely covered on the substrate, which makes the diamond film growth more even. As the temperature rises the diamond film growth rate increases. Howev er, if the temperature is too high, graphitization will occur and the film quality will decrease. The optimal temperature is in the range of 700-800 oC.Based on the above research, in order to further increase the high growth rate and quality of diamond thin films, and we introduce a small amount of nitrogen and oxygen. With the increase of nitrogen concentration the growth rate of diamond film increases gradually. But when nitrogen concentration is too high the growth rate will decrease because of the nitrogen ion bombardment. Although the addition of oxygen can accelerate the oxidation of diamond and decrease growth rate, it will also accelerate the oxidation of amorphous carbon and graphite to improve the quality of the diamond film. It is manifested that the diamond growth rate and quality can be adjusted by adding a small amount of nitrogen and oxygen.Scanning electron microscope(SEM) images show that the surface morphology of diamond is smooth and the crystals are uniform in size with relatively perfect facets, and the preferred orientation is obvious. Raman spectroscopy detection shows that the carbon in diamond film is mainly sp3 hybridization. X-ray diffraction(XRD) shows that the diamond film is well crystallized. The main preferred growth orientation is(111) and(220) surface.