Mechanisms Of Nanosecond Laser Irradiation Of Silicon Carbide

Silicon carbide(SiC)is one of the most suitable semiconductor materials for high-temperature,high-power devices due to its properties such as wide band gap,high breakdown electric field,and high thermal conductivity.However,the strong mechanical hardness and chemical inertness of SiC make it difficult to process and fabricate Micro-Electro-Mechanical System(MEMS)SiC-based devices.Therefore,laser processing is gaining attention as a processing tool with high controllability,high speed,and high quality.This paper focuses on nanosecond laser irradiation of SiC,with an emphasis on the mechanism of laser ablation and modification of SiC.The main research results are as follows.Studies have shown that when laser irradiation is applied to SiC,a uniform layer of damage is formed on the surface of the SiC due to the thermal effect.The highest content of material in the region of 50 nm near the surface was identified as graphite based on component analysis and can therefore be considered as a graphite layer.The conventional heat conduction model is rewritten to consider the effect of phase changes and material distribution and it is revealed that when the number of pulses is greater than one,the temperature distribution during laser irradiation always results in a constant etching depth and the thickness of the new damaged layer,which results in a constant ablation rate.The results obtained based on this model are in good agreement with the experimental phenomena and can explain the formation of the material distribution in the damage layer and the ablation rate that does not vary with the number of pulses,which provides a reference for understanding the laser ablation mechanism.Laser modification of SiC has been investigated based on the experimental phenomenon that a small amount of SiC remains decomposed beneath the damaged layer resulting from laser irradiation.It is shown that the laser modification reaches the micrometer range in the longitudinal direction;the transverse modification is mainly dependent on the temperature distribution on the surface during laser irradiation.Further analysis of the PL spectra in the modified region reveals that the main effect of laser irradiation modification is the introduction of C_SiV_C and V_Siwithin the SiC,and to further understand the nature of both,a comparison between the preparation of ohmic contacts on the modified SiC and direct annealing without modification shows that laser modification favours a reduction in specific contact resistivity.This phenomenon suggests that the C_SiV_C generated by laser modification acts as a donor for n-type SiC.This offers a possibility for the application of laser modification in areas such as laser doping and laser annealing.