Synthesis Of Boron-doped Diamond Films And Research On It’s The Growth Charicteristics By DC-PCVD

Born-doping diamond films with many excellent unique properties such aselectrical properties、extraordinary chemical stability、electrochemical properties、lower surfaceness， is a new and muti-functional materials. It is widely used inelectronic，electrochemistry and mechanical fields.In particular,it also has goodpotential promising in space devices and optoelectronic devices.So far, study ofBorn-doping diamond films is a hot topic in diamond films application research fields.Therefore it is of great significance to study the growth charicteristics of B-dopeddiamond films.In this paper, B-doped CVD diamond films were prepared by direct currentplasma chemical vapor deposition （DC-PCVD） with H₂,CH₄, as well as the boronprecursor carried by H₂through a B（OCH₃）₃liquid, into the chamber.BDD films weredeposited on p-type monocrystalline Si substrates,And the research on the growthcharicteristics of BDD films such as grains morphologies, orientation, crystal quality,resistivity, residual stress and chemical bonding states. The samples were analyzedand charicterized by SEM、XRD、Raman and XPS.The main contents of thesis asfollows:1)The influence of deposited time on the growth charicteristics of polycrystallinediamond films.SEM shows that the size of grains is small in the short deposited time. With theincrement of growth time, the size of grains presents trend of increase. XRD showthat increase of deposited time is favorable for growing {111} facets. Themorphologies of the grains were dominated by {111} facets.Raman shows that thegraphite peak gradually weakened with the increment of growth time. And interestingbroad bands appears around570cm1in the low frequency part due to the fact that asmall number of boron atoms substitutes carbon atom of diamond, This fact shouldbe attributed to the substract Si have impact on born-doping in the short time. 2)The influence of the flow rate of B（OCH₃）₃on the growth charicteristics ofdiamond films.SEM shows that born-doping advantaged to make grain size refinement, andmeanwhile the surface morphologies of diamond grains display more fine. Results ofXRD show that undoped diamond films present （110）facets, while surfacemorphologies of born-doping diamond films were dominated by {111} facets. It isshowed that the born-doping can enhance the growth of {111} facets. Theinvestigations by Raman spectroscopy show that graphite characteristic peak at1580cm-1can be seen in the undoped diamond films and the qualities of undopeddiamond films is poor. Intensity of graphite characteristic peak gradually decreasedand then disappeared with the increase of the boron flow in the born-doping diamondfilms. When the boron doping level is high, graphite characteristic peak is appearedagain. Proper boron doping may be favorable to increase the quality of the diamondfilms.Compressive thermal stress is often found in the undoped diamond films, whileBDD films present tensile stress. Tensile stress of born-doping diamond films firstlyincreased and then decreased when boron doped increased, and it reached maximumwhen B（OCH₃）₃flow up to10sccm.With the increasing of the B（OCH₃）₃flow,the resistivity of born-dopingdiamond films firstly decreases and then slightly increases, and it reachesminimum value which is about5.742×10^-3.cm when B（OCH₃）₃flow is10sccm.Results of XPS in the boron-doped diamond films show that the impurityelement is mainly boron and oxygen. The carbon atoms in the diamond films mainlyexist in the forms of sp3C–C bonding in diamond、C–C bonding in graphite、C–Obonding、and> C=O bonding; Existing form of B atoms in the diamond films is B-Cbonding in B4C, B-C bonding in BC_3.4, B-O bonding in BO. With the increasing of B（OCH₃）₃flow under conditions of heavily Boron-doped, C–C bonding of graphitephase increases,and the quantity of boron atoms which substitute C atoms in thediamond lattice reduces,and then SP³B-C bonding decreases. The more boron atomscombine with amorphous carbon and oxygen atoms,and then SP²B-C bonding andB-O bonding in BOwill be formed. As a result, crystal quality of boron-doped diamond films and the effective doping ability of boron reduce With the increasing ofthe B（OCH₃）₃flow.3)The influences of methane flow on B-doped polycrystalline diamond filmswere researched.The results indicate that the methane flow had no obvious effects surfacemorphologies of B-doped diamond films,and grains size become much bigger whenmethane flow increase. Boron-doped films consist mainly of grains with [111] texturesynthesized at different methane flow. In the Raman spectra of the films we can seecharacteristic peak of nondiamond phase When the methane flow is high.The resultshow that heavily flow of methane reduce crystal quality boron-doped diamond films.With the increasing of the methane flow,the resistivity of born-doping diamond filmsincreases,and it is about6.029×10-2.cm when methane flow is8sccm.4)Effect of gas pressure on the growth charicteristics of B-doped polycrystallinediamond films.When gas pressure is lower than125Torr, the edges and corners of diamondgrains also become more and more trenchant, and meanwhile only sharp diamondcharacteristic peak can be displayed. In the gas pressure range from135Torr to140Torr Surface morphology of B-doped diamond films becomes“cauliflower–like”,andin the Raman spectra of the films we can see graphite characteristic peak at1580cm-1.The higher gas pressure can decrease crystal quality. Therefore, the120Torr-125Torrshould be considered as a desirable value to synthesize the boron-doped diamondfilms with higher crystal quality by DC-PCVD.5)The influences of temperature on B-doped diamond films have been studied.The results from SEM observation and Raman characterization indicate that thetemperature of10500C is a critical value, if it does not exceeds this value,boron-doped diamond films reflect crystal shape clear, and the crystal quality of thefilms is fine; and if it exceeds this temperature, the particles becomes much smallerand and the grains appear in their incomplete shape with unclear boundaries,meanwhile,B-doped diamond films is composed of countless clusters as well ascharacteristic peak of non-diamond phase at1500cm-1～1660cm-1can be seen.Crystal orientation of the boron-doped diamond films consist mainly of （111） facets synthesized at different temperature,and temperature does not affect the crystalorientation of the boron-doped diamond. The result turn out that1000℃is optimaltemperature of BDD films growth.