Effects Of Deposition Conditions On The Growth And Doping Of CVD Diamond Films

Diamond has excellent physical and chemical properties, such as highest hardness, well chemical stability, highest thermal conductivity and high optical transmittance. Due to the scarcity and expense of natural diamond, synthetic diamond has been attracted special attention. A lot of work has been focused on CVD diamond films but there are still many problems on the growth mechanism of diamond films for its complexity. A further understanding of the growth mechanism can help us optimize the deposition condition of CVD diamond and prepare high quality films.In this paper, the nucleation, growth and doping characteristics of diamond films prepared by microwave plasma CVD and hot filament CVD have been studied under different conditions such as substrate pre-treatment, methane, oxygen, nitrogen, power and pressure. The diamond films were characterized by SEM, Raman, XRD. The plasma was measured by OES.1. The results show that pre-treatment and temperature of substrate play an important role in the nucleation of diamond. With scratching of the substrate surface and increasing the substrate temperature, the nucleation density can be enhanced. The polycrystalline diamond film is a result of competitive grain growth.2. High methane concentration can promote the growth rate but deteriorate the quality of diamond films for it can increase the electron temperature of the plasma and the C2 density. Increase of power increases electron density and enhance the gas decomposition which together with high substrate temperature offset the effect of C2, result in good quality and high growth rate of diamond films. The better quality of diamond films can be obtained with oxygen added. Oxygen can not only improve the efficiency of etching of non-diamond phase but also decreases the C2 density. Nitrogen can promote the growth of (100) facet and growth rate. However, too much nitrogen influences the morphology of diamond and results in a nano-crystalline film. After the adding of nitrogen, the optical emission intensity of different particle shows no significant change except CN. The CN behaves like a catalyst which abstracts adsorbed hydrogen from the diamond surface to create growth sites and competes with hydrocarbon and then enhances the incorporation of growth species into diamond lattice. With increasing the work pressure of chamber, the optical emission intensity of all radical increases.3. The study of boron and nitrogen co-doping diamond films shows that Boron can change the effect of nitrogen on the morphology and quality in HFCVD system. With boron and nitrogen co-doping, the quality of diamond films were promoted. Proper proportion of boron and nitrogen can help us optimize the deposition parameters of diamond film growth. The measurement result of OES suggests that boron didn't influence the density of CN. It is considered that it is the competition of boron and CN on the surface of diamond which improves the film quality. The bias has an important role in enhancement of growth species activity. It reinforce the effect of boron and nitrogen. The concentration of boron in diamond film varies with nitrogen flow rate without bias, it perhaps the activity of boron atom and radicals is lower, the absorption of CN on diamond surface decreases the dangling bonds and vacancy of surface by a large mount which prevent the absorption of boron radicals, meanwhile the change of texture of diamond film can also influence the content of boron in diamond films.