Investigation On Homoepitaxial Single Crystal Diamond By MPCVD

Single crystal diamond has a good application in super hard materials,optical devices,electronic devices and other fields,and it also shows great market prospects in the field of decoration.Because of its advantages of no discharge pollution,high deposition rate and strong controllability,microwave plasma chemical vapor deposition（MPCVD）is considered as the best method for preparing single crystal diamond.The main difficulties in the growth process are focused on the control of defects,the improvement of the rate,and the production.In view of the difficulties mentioned above,this research carried out the research on homogeneous epitaxial single crystal diamond on the 2.45 GHz,10 kW new multimode resonant cavity MPCVD device independently researched and developed by the laboratory.The main research contents are presented as follows.Firstly,the effect of methane concentration and deposition temperature on the homoepitaxial single crystal diamond under high power has been studied.The results show that the surface morphologies of the single crystal diamond are firstly dominated by terraced shape and then transform to be dominated by laminar shape with the increase of methane concentration.The quality of the diamond is declining as the epitaxial rate increases.The surface morphologies of the single crystal diamond are firstly dominated by step-flow growth and then transform to be dominated by hillock growth with the increase of temperature.The epitaxial rate and the quality of single crystal diamond are both increasing firstly and then decreasing.Diamond film with 3.69 cm^-11 as FWHM value of diamond peak of raman spectrum is obtained when the deposition temperature is 900℃and the methane concentration is 10%.Secondly,the impact of the H₂/O₂ plasma etching on diamond was investigated.The results show that the effect of pure hydrogen etching is weak,while the role of oxygen etching is more effective.The etch surface was firstly dominated by flat-bottom pits and then transformed to be dominated by pointed-bottom pits with the increase of etching time.The density and size of etching pits both increase with the increasing etching time.The micro-defects on the surface of the single crystal diamond can be reduced and the quality of homoepitaxial single crystal diamond can be improved by H₂/O₂ plasma etching.The crystallinity of single crystal diamond is better within 1 hour.Thirdly,the reasons of the formation of growth defects during epitaxial single crystal diamond were studied,and the deposition process of epitaxial single crystal diamond has been improved.The results show that the stress is higher in the high defective density area of diamond,which can easily affect the mode of homoepitaxial single crystal diamond.By adopting the two-step method of first depositing with 1%oxygen for 1 hour and then stopping the introduction of oxygen to continue epitaxial growth,the driving force of the secondary nucleation and defects in the epitaxial process can be reduced.Finally,when the microwave power is 5000 W and the pressure is 15 kPa,a stable plasma ball with a diameter of 100 mm is obtained.In this deposition environment,eight single-crystal diamonds can be grown at the same time.The maximum deposition rate is 32μm/h,and the maximum size is 5×5×2.5 mm³.The basic conditions for batch production of single crystal diamond is obtained.