Ultra-fast Preparation Of 3C-SiC Thick Films By Halide Laser CVD

3C-SiC is a promising functional material due to its many attractive features,such as low density and thermal expansion coefficient,high temperature stability and thermal conductivity,thermal shock,oxidation and corrosion resistance.Chemical vapor deposition?CVD?has been often used to prepare SiC thin films.However,the low deposition rate(R_dep)of conventional CVD process such as hot wall or cold wall CVD,low pressure CVD,plasma enhanced CVD has raised the costs of fabricating3C-SiC thick films.Because of the high R_dep,infrared laser CVD has been used extensively to deposit thick films.Among several precursors that used in the preparation of 3C-SiC films,halide precursor such as SiCl₄ has attracted much attention due to its low cost and high R_dep.Therefore,in this study,a haide laser CVD?HLCVD?would be developed by combining the advantages of infrared laser CVD and halide precursor to rapidly prepare 3C-SiC thick films.Fine grained 3C-SiC has many superior mechanical,electrical and optical properties to their large grained bulk counterparts.Fine grained 3C-SiC thin films were often prepared at low T_dep by hot wire CVD,plasma enhanced CVD and photo CVD.Because of the low R_dep,it was difficult to obtain thick films in these CVD process,thus restricting its applications.3C-SiC thick films could be rapidly prepared by infrared laser CVD,however,with increasing the thickness of 3C-SiC films,the average grain sizes of 3C-SiC thick films were also raised to tens or hundreds micrometers.Ultraviolet pulsed laser was commonly used to deposit 3C-SiC films at low temperature in photo CVD.On the other hand,another important application of ultraviolet pulsed laser was surface treatment of 3C-SiC.When 3C-SiC substrate was irradiated by an ultraviolet pulsed laser,tiny structures would be obtained at the surface of 3C-SiC.In order to speedily prepare fine grained 3C-SiC thick films,in this study,infared continuous laser CVD and ultraviolet pulsed laser CVD were combined together to develop a hybrid laser CVD.The research work and major conclusions are listed as follow:At T_dep=1673 K and P_tot=10 kPa,3C-SiC thick films were fabricated by halide laser chemical vapor deposition?HLCVD?at different R_C/Si using SiCl₄,CH₄ and H₂as precursors.At RC/Si?0.75,continuous 3C-SiC thick films were deposited,however,island-like and incontinuous of 3C-SiC was obtained at R_C/Si=1.At R_C/Si?0.5,stoichiometric 3C-SiC thick films were obtained,however,free carbon was co-deposited in 3C-SiC at R_C/Si?0.75.The density of 3C-SiC was dramatically decreased at R_C/Si=1 due to the large amount of free carbon.Highly oriented 3C-SiC thick films were fabricated by HLCVD at different P_tot and T_dep.The P_tot and T_dep had great influence on the preferred orientations of 3C-SiC thick films.The<110>-oriented 3C-SiC thick films were obtained at low P_tot??4 kPa?and much higher T_dep?>1473 K?,<111>-oriented 3C-SiC thick films were obtained at high P_tot?10–40 kPa?,and random oriented 3C-SiC thick films were obtained at intermediate parameters.The maximum R_dep of<111>-and<110>-oriented 3C-SiC thick films were 3600 and 1300?m/h,respectively.At T_dep=1623 K,transparent 3C-SiC thick films were speedily fabricated by HLCVD at different P_tot.With an increase in P_tot,the transmittance of 3C-SiC thick films increased firstly,and then decreased.At P_tot=10 kPa,3C-SiC thick film,a highly<111>-oriented and low density of defects,showed the highest transmittance,greater than 55%in the wavelength range of 800 to 1100 nm.The transmittance of 3C-SiC thick films was significantly affected by the poor orientation and defects.At P_tot=4 kPa and 20 kPa,3C-SiC thick films showed much lower transmittance due to the vast poorly oriented grains and defects in 3C-SiC thick films.At P_tot=4 kPa and T_dep=1523-1623 K,fine grained 3C-SiC thick films were speedily deposited by a hybrid laser CVD which was composed of ultraviolet pulsed laser CVD and infrared continuous laser CVD.The grain sizes of 3C-SiC thick films prepared by infrared continuous laser CVD were ranged from 4-100?m,however,fine grained 3C-SiC films with grain sizes in the range of 0.5-5.5?m were obtained by hybrid laser CVD.Compared with 3C-SiC thick films deposited by infrared laser CVD,the Vickers micro-hardness of fine grained 3C-SiC thick films prepared by hybrid laser CVD was improved due to the much smaller grain size.