The Research Of Synthesis Technology And Mechanism On Diamond Films At Low Temperature In MWPCVD

Diamond is a remarkable material due to its special crystal structure, which shows high hardness, low friction coefficient, high thermal conductivity, high optical transparency, low permittivity and high band gap etc. CVD diamond films are widely used in mechanical coating, heat sinks, optical window, semiconductor devices and other application fields because of its low price and high performance.Typical temperature is 800-1000℃ in CVD diamond process, while the high temperature limits its application in optical window and coating such as GaAs, ZnS etc. Low temperature can not only make diamond crystal nucleus finer, reduce surface roughness of diamond films and lessen light dispersion, but also eliminate thermal stress.Diamond films were deposited using in CH4/Ar/Hk gas system and silicon (111) wafers substrate in MWPCVD-4 at low temperature. The effects of the gas system and proportion, different microwave power, different reaction pressure and different pretreatment methods of substrate and the position of substrate on the microstmcture of diamond films were respectively discussed in this paper. The three different pretreatment methods were adopted respectively in order to increase nucleation density.(1)Silicon substrate was pretreated by diamond abrasive;(2) Silicon substrate was pretreated by seeding of suspending diamondslurry;(3) Silicon substrate was pretreated by diamond abrasive and seeding of suspending diamond slurry.The result shows that Argon gas can not only promote the excitation of plasma at low pressure, but also improve discharge state, increase the density and activation of reaction radical and improve the quality of diamond films. On the other side, Argon can cool the plasma and maintain low temperature of substrate due to its big ionization section and high collision probability with gas molecules. When the third pretreatment method was adopted, microwave input power was 700W, gas pressure was 1000Pa and substrate was tangent on plasma ball surface, diamond films showed higher nucleation density by contrast.At last, the diamond film samples were investigated by X-ray-diffraction (XRD) and Scanning Electron Microscopy (SEM) in this paper.The result shows that diamond (111) peak is indicated in X-ray-diffraction patterns, and diamond peak is very low because of non-diamond phase and defects. The SEM images of diamond film shows that diamond films are stacked with regular ranged and about 200nm ball-like diamond secondary nucleation particles. The diamond films show no well-faceted particles.