| As the material with the highest hardness in the nature,diamond not only has high commercial value in the jewelry market,but also is widely used in the traditional industrial applications.Such as,in mechanical processing as a high hard cutting tool,grinding wheel,grinding particles,in drilling and mining as a drill,in a variety of precision instruments as an optical window.These applications only take advantage of diamond’s superhard properties,very low coefficient of friction,very low coefficient of thermal expansion,chemical stability and optical properties.In recent years,with the development of diamond preparation technology,diamond have attracted the attention of scholars from all over the world due to its semiconductor properties,such as broadband gap,high thermal conductivity,high breakdown voltage and high carrier mobility.Because of the low reserve and high price of natural diamond,the preparation of high quality and large area single crystal diamond has always been an important research topic.At present,the widely used synthesis techniques include High Temperature and High Pressure method(HTHP),Microwave Plasma Chemical Vapor Deposition(MPCVD),Hot Filament Chemical Vapor Deposition(HFCVD),etc.MPCVD homogeneous epitaxial growth on HTHP substrate is an important preparation solution.However,there are still many scientific and technical problems in the preparation of single crystal diamond.The first primary problem is the processing of diamond.Its super-precision machining is very difficult,due to the super-hard property of diamond.Both the epitaxial growth and the manufacturing of electronic devices require the surface roughness of single crystal diamond to reach the nanometer level.Therefore,in this paper,the processing of superhard diamond was studied,and a four-step processing process including orientation,cutting,grinding and polishing was established.After the surface orientation of HTHP diamond by Laue method,the bulk single crystal diamond is cut by laser into a wafer.There are a large number of graphite layers and cutting marks on the surface of flake diamond,which result in uneven surface.The grinding is a process to remove the cutting marks of laser cutting.The(100)and(110)of type HTHP diamond(HTHP Ⅰb)were investigated along the<100>,<110>by grinding.The surface after grinding was compared by Atomic Force Microscope(AFM),Laser scanning confocal microscope(LEXT)and other characterization methods.Surface/Subsurface damage still exists after mechanical grinding.So ultra-precision machining is carried out by chemical mechanical polishing.The surface roughness is reduced to 0.7nm.The application in semiconductor field requires higher quality of single diamond materials.In addition to the surface state of the substrate after processing,the type of single crystal diamond,the time of homogeneous epitaxial growth,various parameters of the growth process,and the deviation angle of the(100)crystal plane of the substrate will all affect the crystal quality.In this paper,it is focused on the differences between HTHP Ⅰb,Ⅱa HPHT type diamond(HTHP Ⅱa)and MPCVD type diamond(MPCVD)by Raman,HRXRD characterization and plasma etching.And the MPCVD homogeneous epitaxial growth for 8h and 16h difference were observed.FWHM of Raman and HRXRD are broaden along with the duration of growth.H2 and H2/O2 plasma etching were performed on HTHP Ⅱa,HTHP Ⅰb and MPCVD(100)surfaces.The etch rates(ER)from 900℃to 1300℃were measured.At the same temperature,ER(HTHP Ⅰb)>ER(HTHP MPCVD)>ER(HTHP Ⅱa).ER showed Arrhenius type temperature dependence,and activation energy(Ea)was calculated.Under H2/O2 etching atmosphere,Ea(HTHP Ⅰb)>Ea(MPCVD)>Ea(HTHP Ⅱa).Under H2 and H2/O2 etching atmosphere,Ea(H2/O2)>Ea(H2).Further more,the surface of samples before and after etching was tested by X-ray photoelectron spectroscopy(XPS)to analyze the changes of carbon-containing groups in C1s spectrum.After H2 etching on surface(100)of HTHP Ⅰb sample,the content percentage of CHx group and sp2C-N group increased.It is implied the nitrogen doping accelerated the etching rate.After H2/O2 etching,the content percentage of CHx group,sp2C-N group,C-O group,C-O group and-COOH group increased,indicates that the addition of O component in the plasma increases the etching rate.The HTHP Ib(100)surface was etched with H2,O2/H2=1.50%,O2/H2=2%,O2/H2=3%,O2/H2=4%,O2/H2=5%plasma,respectively.The etching pit morphology was observed by LEXT,and the change of etching pit size and morphology was recorded with the etching time.At the same time,the shape change of flat bottom engraving and sharp bottom pit with etching time is studied,and the flat bottom engraving will become larger and flattened with etching time until it disappears. |
