Research Of The Large-area Optical-grade Diamond Films

CVD diamond films own a wide range of application prospects due to their numerous excellent physical and chemical properties.Whereas,the large-area optical-grade diamond films have a wilder application in all fields owing to their structural integrity,especially in the fields of national defense and energy.which makes them a focus.Among the numerous ways of CVD diamond films deposition,Microwave Plasma Chemical Vapor Deposition?MPCVD?is the best one on account of pure deposition atmosphere and high density plasma it offers.In this paper,a serial of deposition parameters were investigated in home-made non-cylindrical multimode MPCVD device,in order to lay the foundation of large-area optical-grade diamond films deposition.The primary results in this research are listed following:1.The mainstream MPCVD device are introduced,so did their electric field distribution with the help of Comsol Multiphysics software.The effects of MPCVD device structure and electric fields distribution on large-area optical-grade diamond films are discussed.The research results indicated that,compared with other MPCVD device,the home-made non-cylindrical multimode MPCVD device used this paper is the best one serving as large-area optical-grade diamond films deposition,which can offer high-density large-size plasma over the substrate holder for a long time.In addition,the simulation of the electric field distribution shows that,the parts where the microwave antenna exists are strong electric field area,compared with ordinary electric field coupling MPCVD devices,which provides a basis for the water cooling structure design and the machining accuracy of the antenna.2.First,the effects of deposition pressure and microwave power on the coupling between the microwave and the plasma were discussed by the way of theoretical calculation and numerical simulation.Then,the effects of deposition pressure and microwave power and their coupling on diamond deposition were explored.The results showed that,with the increase of the deposition pressure and microwave power,the hydrogen concentration in the plasma significantly enhance,C₂ group concentration changes rarely,the CH group concentration firstly increased and then decreased,the substrate temperature rise more slowly,the diamond grain shifts from pyramid-shaped to poker style.There is a optimal deposition pressure for the specific microwave power parameter,under which,the coupling efficiency between the microwave and plasma is the highest,and the MPCVD device can run stably for a long time,which is to the benefit of large-area optical-grade diamond deposition.3.The effects of gas flow rate on diamond grain morphology,quality,and growth rate were explored with the optimization of deposition pressure and microwave power,and so were the MPCVD device flow field distribution and improvement suggestions.The results made clear that,with the increasing of gas flow rate,the diamond quality and growth rate firstly increased and then decreased,the diamond grain size diminished gradually,and going so far as to predict Nano-crystalline diamond?NCD?under the condition of higher gas flow rate.Besides,the MPCVD device flow field stability is pretty well,there was no turbulent flow even under the condition of higher gas flow rate.Last but not the least,the distribution of the flow field velocity over the substrate holder were relatively uniform.A new-typed substrate were designed in order to further improve the uniformity.Taking the growth rate,quality and uniformity of the diamond films into account,the ideal gas flow rate used in large-area high quality diamond films deposition is 300 sccm.