Growth Of Diamond Particle With High Quality Through MPCVD

Diamond, especially large-size single crystal diamond (SCD) is much requiredfor the purpose of meeting the needs of its application in the field of electronics whereit is the most attractive. HTHP and CVD techniques used most widely have maderemarkable achievement in the preparation of large diamond particle with high quality.Compared with the HTHP, CVD has more potential in this aspect due to itsadvantages, such as in principle no restriction on the size of diamond particlesynthesized, effective control in doping and low cost of equipment. MPCVD haveattracted more attention due to high quality, high growth rate and low depositiontemperature in synthesizing single crystal diamond. So far, MPCVD has achievedgreat progress in homoepitaxial growth of large-size, high-quality SCD. Buthomoepitaxy of diamond requires natural diamond or HTHP diamond seed with highcost, additionally, the size of diamond synthesized is limited in the size of the seedused. In contrast, the growth of diamond particle on heterogeneous substrate has noproblems existing in hemoepitaxial diamond. Some studies on the growth of largediamond particle on heterogeneous substrates have been reported, but the size of thediamond particles are small (typically less than300μm), and the surfaces of somediamond particles are even covered by numerous secondary nucleations andmicro-crystals. The purpose of this study is to grow large diamond grain with highquality and smooth surfaces.In order to grow a large diamond particle with high quality on a foreign substrate,diamond films consisting of by diamond grains with a smooth (100) facet at its top arefirstly needed, which was indicated through literature researches. So the growthconditions of the smooth (100) oriented diamond films were explored in this paper atfirst. Due to N2addition has significant influences on morphology and texture ofdiamond films, the influences of different amounts of N2on morphology, texture andquality of diamond films were firstly studied in this work. Finding when thepercentage of the N2/CH4is1%, diamond films consisting of diamond grains with asmooth (100) facet at their tops are favored. But the further enlargement of the sizes of these diamond particles composing of diamond films is limited because of the highnucleation density of diamond during nucleation stage. O2addition has an importanteffect on the diamond nucleation, so a research on effects of different flow rates of O2addition into mixed gases on diamond nucleation was made in the next section. Theresults showed when the flow rate of O2was2.0sccm, the nucleation density ofdiamond was moderate and the morphology of diamond nucleation showed almostcubic-octahedron with smooth surfaces. Diamond with large size and high quality wasgrown on the above two studies. After100h, a500μm of diamond particle at5μm/h ofgrowth rate was obtained. SEM characterization revealed that the top the largediamond particle showed a smooth (100) facet with a size of about250μm, and italmost paralleled to the surface of substrate. The Raman characterization about thelarge diamond particle only showed a very sharp diamond peak at1332cm-1,indicating its high quality. Next, the formation mechanism of the large diamondparticle was discussed from macroscopic and microscopic aspects. In respect of macromethod, the O2addition during nucleation stage and the N2addition during the first10h of the growth stage provided a requisite precondition for the growth of the largediamond particle. But the formation of the large diamond particle is the result of thegrowth parameters, such as high ratio of CH4/H2(5%), high growth pressure(15.4~16.0kPa)，high substrate temperature (830~900℃), combined with the MPCVDequipment. In respect of micro method, two model, microwave discharge simulationmodel and large SCD growth model, was adopted to show the necessary conditionsfor the synthesis of the large diamond particle with high quality. Finding that highconcentration of hydrogen ([H]) and growth channel dominated by monoradical sitesare indispensable. Finally, a comparison about similarities and differences of resultsbetween J.B.Donnet’s and ours was made. Finding the morphologies of diamondparticles are very similar to each other in the two experiments, but not only the sizebut also the quality of the diamond particle in our experiments is advantageous, whichis respectively caused by the different nucleation density and CVD methods used intheses two experiments. Otherwise, there are two commons in the two experiments.One is thinking that the first obtainment of the smooth (100) facet at the top of diamond particle provides preconditions for subsequent growth of the diamondparticles, and the other is thinking that high substrate temperature increases thegrowth rate and the particle size.