Synthesis Of Single Crystal Diamond With Low Nitrogen Concentration

Diamond has received much attention because of its excellent properties such as high electric breakdown strength,high carrier mobility and high thermal diffusivity.Obtaining high purity and high quality diamond materials is a prerequisite for achieving these excellent properties.However,both natural diamond and synthetic HTHP(High Temperature High Pressure)diamond are not of the quality required for modern semiconductor devices due to their high impurity content and excessive crystal defects.With the development of Chemical Vapor Deposition(CVD)technology,artificial diamond has become possible as an electronic material.At present,the main method to obtain high purity and high quality single crystal diamond(SCD)is to introduce a mixture of carbon-containing gases in a vacuum chamber reactor and use microwave plasma for chemical vapor deposition(Microwave Plasma Chemical Vapor Deposition,MPCVD).MPCVD)method to obtain high purity single crystal diamond.Due to the late start of CVD technology in China,there is a gap in the preparation of single-crystal diamond with low nitrogen content compared with foreign countries.In this study,the homogeneous epitaxial growth of low nitrogen single crystal diamond was investigated by using 6 k W MPCVD equipment,and the main research contents are as follows.1.Etching study of diamond seed crystals,when etching 1.0 h,2.0 h and 3.0 h,respectively,to obtain a better etching effect on the surface of single crystal diamond seed crystals at etching time of 2 h,for the pre-treatment of homogeneous epitaxial growth.2.The study conducted three sets of growth tests at CH4 concentrations of 1%,4%,and 10% to investigate and obtain the suitable single crystal diamond homogeneous epitaxial growth process at CH4 concentration of 4%.The verification of etching and epitaxial growth process at CH4 concentration of 4% provides the process basis for further research on reducing the nitrogen concentration later on.The nitrogen reduction study of single crystal diamond was carried out under the research base conditions of 1 & 2.3.The results show that as the nitrogen content in the diamond growth atmosphere increases,the diamond growth rate first increases and then decreases,and the nitrogen concentration in the diamond growth layer shows an increasing trend.4.The effects of the width and depth of the molybdenum block grooves in the vacuum chamber on the nitrogen content of the grown diamond growth layer were studied.The results showed that the width of the molybdenum block notch had no significant effect on the nitrogen concentration and growth rate of the grown diamond layer,while when the depth of the notch increased,the nitrogen concentration in the grown diamond layer decreased,and the growth rate of the diamond decreased at the same time.5.The effect of the initial vacuum level of the vacuum chamber on the nitrogen concentration in the grown diamond growth layer was investigated.The results were characterized by EPR(Electron Paramagnetic Resonance)under different initial vacuum levels for 4.0 h.The results showed that the higher the initial vacuum level,the lower the nitrogen concentration in the diamond growth layer,and the growth rate tends to decrease.In this study,the high quality single crystal diamond growth process was investigated by seed etching and carbon concentration control.Based on this,different nitrogen content reaction gases were introduced for diamond growth,and the results showed that the higher the nitrogen content in the vacuum chamber,the higher the nitrogen concentration in the diamond growth layer.By changing the size of the molybdenum block recess and the initial vacuum level of the vacuum chamber to change the plasma sphere state of the crystal growth surface and the residual gas content of the vacuum chamber to achieve the effect of reducing the nitrogen concentration,the results of the study show that the deepening of the molybdenum block recess and the increase of the initial vacuum level of the vacuum chamber can reduce the nitrogen content in the diamond growth layer.This study provides a solution for the preparation of single crystal diamond with low nitrogen content.