Study On Crystal Control And Optical Transmittance Of Diamond Film Prepared By MPCVD

Diamond has a series of excellent physicochemical properties.Optical-grade and electronic-grade diamonds play an irreplaceable role in high-end fields such as aerospace,nuclear fusion and X-ray detectors,which are considered to be one of the materials with development potential in the 21st century.The MPCVD method is generally regarded as an excellent method for preparing high-quality diamond thin films.The high-power and high-pressure environment is an effective means to improve the deposition rate of the diamond film and optimize the quality of the crystal form.Therefore,it is very necessary to study the regulation of the diamond film crystal form under the high-power and high-pressure plasma atmosphere.In this paper,the 10k W-2.45GHz loop antenna resonant cavity MPCVD device is used to study the process of diamond film crystalline adjustment and light transmittance under high power and high pressure atmosphere.At the same time,the 75k W-915MHz MPCVD device was used to study the uniformity and crystal form of the diamond film,the specific contents are as follows:1.Comsol software was used to simulate the electric field strength and distribution of the 2.45GHz MPCVD device under different input powers on the substrate table.The results showed that the electric field strength and range above the substrate table under high power were significantly improved,which was good for generating suitable environment for high-quality diamond films deposited.2.2.45GHz MPCVD equipment under high power and high pressure was used to study the process factors affecting the diamond film crystal form,starting from different pretreatment,air leakage rate,CH₄ concentration and deposition time conditions.The result show that the uniform scratch density was beneficial to the deposition of diamond films with high flatness and good crystal form consistency;serious secondary nucleation and cavity content was caused by the incorporation of nitrogen at high air leakage rate;CH₄ concentration has great influence on diamond crystal morphology,among which,diamond crystal morphology under 1.5%?2.5%CH₄was better;with the extension of the deposition time,the size of the grain increases,the complexity of the type of crystal form is reduced;finally,a self-supporting film with a diameter of 50mm and good light transmission was prepared at a power of 5.3k W,a pressure of 15k Pa,and 2.5%CH₄.3.The Comsol software was used to simulate the electromagnetic field distribution of the 915MHz MPCVD device at different input powers,water-cooled table size deviations and different substrate table heights,The result showed that the electric field strength and the strong field area above the substrate stage were significantly increased at high power;the size deviation of the water-cooled stage of the device has a large influence on the spatial electric field distribution,superposition mode,and plasma state;the change in the height of the substrate stage has larger impact on a radial electric field distribution above the substrate stage,and estimated a more suitable height range of 20?35mm.4.915MHz MPCVD device was used under high power to study the effect of the substrate stage height on the uniformity and crystal form of the large area diamond film,the results show that the substrate stage height and size have an effect on the electric field distribution and plasma spatial position,and affects the uniformity of large-area diamonds.A diamond film with a good color and a uniform crystal form diameter of 100 mm was prepared at a height of 25 mm,and a diamond film with a good color and a uniform crystal form diameter of 150 mm was prepared at a height of 27 mm at last.