Research Of The Optical Grade Diamond Films Deposition By MPCVD With The High Power

Diamond has excellent physical and chemical properties,and high quality diamond film is considered as one of the most promising materials in the 21st century due to its good application in high-tech fields such as aerospace and high-temperature nuclear fusion.At present,the microwave plasma chemical vapor deposition（MPCVD）technology is generally considered as the preferred method for synthesizing high quality diamonds because of electrodeless discharge and high concentration of plasma energy.In the process of diamond deposition by MPCVD technology,the increase of microwave power is an effective means to improve the quality and growth rate of large-area diamond film.Therefore,the growth of diamond film under high power microwave plasma is of great significance.In this paper,based on the laboratory-made 10kW MPCVD system,the characteristics of high-power plasma discharge environment were analyzed,and the preparation process of optical-grade diamond film under high power conditions was systematically studied.What’s more,some research on the 75kW high-power MPCVD system with 915MHz microwave frequency had conducted.The specific contents are as follows:1.The microwave electric field in the cavity of 10kW,2.45GHz device was simulated under different high microwave power.The results showed that the strong electric field formed by the superposition of the TM₀₁1 and TM₀₂2 modes exists stably above the substrate,and with the increase of the microwave power,the electric field intensity increased and the area of the strong field area also expanded relatively.Combined with plasma multiphysics coupling simulation and spectral analysis results,it was believed that the plasma activity under high power conditions was higher and the area was larger,which was favorable for the preparation of high quality diamond films.According to the distribution characteristics of microwave electric field on the surface of the substrate,the structure of the substrate holder was designed,and the optimum height of the substrate holder was 6mm.2.The emission spectra for the plasma of the 10kW device were investigated at different high power.By the emission spectra diagnosis of CH₄/H₂ plasma at different power,it was found that the increasing of the power was beneficial to increase the energy of the main active groups in the plasma,and the uniformity of its distribution was increased.And it was found that when the microwave power increases from3500W to 5500W,the electron density increased and the electron temperature decreased gradually by specific calculation,which proved that the high-power microwave plasma had extremely high activity,and this feature was favorable to the preparation of high quality diamond films.3.The growth process of optical grade diamond films under high power conditions was studied on the 10kW device.Experiments showed that different concentrations of methane had significant effects on the plasma、the surface morphology and quality of the diamond film.Comprehensive analysis showed that2%was the best methane concentration;the addition of oxygen accelerated growth rate of the film,while also significantly improved the overall quality of the diamond film,and the best oxygen concentration was 0.7%.A homogeneous optical grade diamond film with an infrared transmittance of 58%and a diamond Raman FWHM of6.5 cm^-11 was prepared at a hydrogen/methane/oxygen flow ratio of 300/6/2.1.4.Emission spectrum detection confirmed that the 75 kW,915 MHz MPCVD device can generate a uniform plasma sphere with a diameter of at least 6 inches when the microwave power was 20kW and the pressure was 13kPa,and the electron density was symmetrically distributed with higher energy.Diamond film was prepared by pre-experiment under different methane concentration conditions,and the FWHM was about 5.1cm^-1.Then some reasonable improvement suggestions were proposed for the hardware facilities and industrial process research of the MPCVD system.