Structure Control And Performance Research Of SiC Thick Films Deposited By Chloride Laser Chemical Vapor Deposition

3C-SiC thick films（>10mm）have excellent characteristics such as high hardness,high thermal conductivity,chemical stability,wide band gap and high electron mobility,and widely used in the field of structural coatings and semiconductor devices.The crystal structure of 3C-SiC determines its performance.To date,the research of 3C-SiC structure has been widely reported,but the interaction between structure and performance and coresponding mechanism was still unclear.This study prepared 3C-SiC thick films via chloride laser chemical vapor deposition,and uncover the relationship and mechanism of the mechanical and electrical properties of SiC thick film and its microstructure.Firstly,MTS and SiCl4 with CH4 were selected as the precursors,an infrared continuous laser was used as the excitation source to prepare 3C-SiC thick films.The results show that the SiC thick film prepared with MTS as the precursor is prone to co-deposit with impurities at high pressure（Ptot=40 k Pa）.At low pressure（Ptot=4/6k Pa）,3C-SiC displays<111>preferred orientation,and the rest show<110>orientation.The maximum deposition rate is 390mm/h;The SiC thick film prepared via SiCl4 and CH4 deposited at all experimental parameters show stoichiometric.With the increase of Ptot,the orientation of 3C-SiC thick film gradually changes from<110>to<111>,and the maximum deposition rate is 2842mm/h.The results show that SiCl4is more suitable as a precursor to regulate the structure of SiC thick films.In addition,this study uses EBSD to get further insight on the microstructure and growth mechanism of the<110>-and<111>-oriented 3C-SiC thick films.Among them,there are a few stacking faults（SFs）in the<110>-oriented SiC thick films parallel to growth direction,and the density of SFs is about 4×10³mm^-2.<111>-oriented SiC thick film has a high density of SFs in the vertical growth direction,and the density of SFs is about 1×10⁷mm^-2.The growth process of the two oriented SiC thick films can be divided into three stages.The randomly oriented small grains growth near the graphite substrate for a short period of time,and then the<110>-oriented SiC thick film changes from the the<111>-oriented elongated grains to the<110>-oriented columnar grains,and the<111>-oriented SiC thick film undergoes a long-term grain competition growth and then transformed into<111>-oriented columnar grains.Secondly,the influence of phases,grain size and preferred orientation of SiC thick film on its mechanical properties were investigated.The results show that the hardness of pure SiC thick film is higher than that of SiC co-deposited with impurities.The hardness of SiC thick film increases with the decrease of grain size（Hall-Petch relationship）.The hardness of<111>-oriented SiC thick film is higher than that of<110>-oriented SiC.Due to the SiC prepared by CVD has the characteristics of high purity,density and preferred orientation,the hardness and wear resistance of laser CVD-SiC are better than those of sintered SiC.In addition,this study uses hybrid laser to further reduce the grain size of SiC thick film and improve its mechanical properties.The results show that the SiC prepared via infrared laser has a columnar crystal morphology with a grain size of 5-100mm and a microhardness of 31 GPa,while the SiC prepared via hybrid laser has an equiaxed crystal morphology with a grain size distribution of 0.5-5mm,and its microhardness increased to 35 GPa.Based on the experimental results and analysis,the action mechanism of ultraviolet laser in chemical vapor deposition was proposedFinally,the relationship and mechanism between the microstructure of SiC thick film and electrical conductivity（s）were investigated.In intrinsic SiC,the grain size and defect density determine thes.The maximumsreaches 4.8 Sm^-1 When the the grain size is 35mm and the defect density is 4×10³mm^-2.For improve thes,the second phase was introduced into the process of SiC deposition.When the flow rate of SiCl4,CH4 and H2 were fixed at 200,200 and 5000 sccm,respectively.Uniform C/SiC composite film was obtained,and thesreaches 2.5×10⁴ Sm^-1,which is 10²-10⁷times than the intrinsic SiC thick film.Besides,high conductivity<110>-oriented3C-SiC thick film were prepared by in-situ nitrogen doping.Thesof N-doped3C-SiC first increases and then decreases with the increase of the N2 volume fraction(f_N2),reaching the maximum value of 740.7 Sm^-1 whenf_N2=20%.<110>-oriented SiC has lower Young’s modulus than that of<111>-oriented SiC,which is expected to improve its sensitivity as a pressure sensor.