Design Of High Power MPVCD Reactors And Synthesis Of High Quality Diamond Films

Developing high power MPCVD reactors is the most effective way to efficiently deposite large area and high quality diamond films, as it is well known that high power MPCVD reactors could produce high density plasma rich in both atomic hydrogen and hydrocarbon radicals which would make it possible to produce diamond films at high growth rates.However, several different types of high power MPCVD reactor both at home and abroad which can run at6-8kW have their own deficiencies more or less. In order to further improve the level of high power MPCVD technology for diamond film deposition, systematically researching on high power MPCVD technology was carried out in this paper.Firstly, by systematically simulating and analyzing the distribution of electric field inside various TM021mode cavity type MPCVD reactor both at home and abroad, the intrinsic relation of various TM021mode cavity type MPCVD reactor was revealed. Based on this, a new procedure for designing MPCVD reactor was put forward. Actually, the new design procedure is just an embodiment of the principle that the electric field vector be perpendicular to the surface of any electric conductor. With this principle in mind, a new TM021mode cavity type MPCVD reactor for diamond films deposition was derived. High quality diamond films were deposited using the new reactor at6kW high microwave power levels, and such a result validates the new strategy in designing the MPCVD reactor.Secondly, by employing above new strategy in designing the MPCVD reactor, a new circumferential antenna ellipsoidal cavity type MPCVD reactor was proposed and built. The new MPCVD reactor possesses a unique structure that adopts an ellipsoidal cavity as its deposition chamber and a circumferential antenna in its microwave coupling channel. A ring-shaped quartz window in the microwave coupling channel has replaced the quartz bell jar that has been used in conventional ellipsoidal cavity type MPCVD reactors. Such a design makes the newly built MPCVD reactor, on one hand, could ignite intense and spatially stable plasma for diamond film deposition, just like in an ellipsoidal cavity type MPCVD reactor; on the other hand, it eliminates the etching and overheating problem of the quartz window by plasma, just like in a multimode non-cylindrical cavity type MPCVD apparatus. And experiments show that the novel MPCVD reactor combining so many excellent capacities can deposit diamond films steady under conditions of input microwave power of about12kW.Based on the successful establishment of the circumferential antenna ellipsoidal cavity type MPCVD reactor, series of experiments were undertaken to investigate the best process parameters for depositing high quality diamond films under6-11kW high microwave power levels. Firstly, three traditional parameters such as the concentration of CH4, deposition temperature and gas flow rate that impact on the process of diamond film deposition were studied. The results show that diamond films grow best when the deposition temperature near890℃, methane concentration near3%, and gas flow rate greater than200sccm. Secondly, the patterns of the gas flow that are associated with the MPCVD reactor itself was studied. The results show that the patterns of the gas flow can not affect the process of diamond film deposition when the the vacuum performance of the reactor is perfect. Finally, With the the circumferential antenna ellipsoidal cavity type MPCVD reactor running at10.5kW high microwave power, a Ψ50mm high quality free-standing diamond film was successfully deposited under the optimum conditions. The growth rate of the diamond film was about6μm/h that is four times more (at the same leak rate of about2.5X10-6Pam3/s for the reactor) than the one deposited at6k W. The thickness of the diamond film is approximately960μm, and the deviation of the thickness is less than±2%. Test results showed that the polished diamond film was colorless and fully transparent, and possessed excellent characteristics such as FWHM of Raman peak of only1.8cm-1, a cutoff wavelength of225nm. a nitrogen content lower than1.5ppm and transmission near71%in the6.5-25μm range.Finally, by combining the structural advantages of the TM021mode microwave resonant cavity and the circumferential microwave coupled antenna, a75kW,915MHz cylindrical ladder-shaped circumferential antenna cavity type MPCVD reactor was proposed and build. Experimentally,(Ψ127mm high quality diamond films were deposited using the newly developed reactor at60kW input microwave power levels. The growth rate of the diamond film can reach4.64μm/h, and the width at half maximum of the diamond peak is approximately2.5cm-1.