飞秒激光的波长对SiC材料烧蚀的影响

利用10倍的显微物镜将近红外飞秒激光脉冲汇聚到宽带隙半导体材料6H SiC的前表面,研究样品的烧蚀及诱导微细结构。用扫描电镜(Scanning electron microscope,SEM)及光学显微镜测量烧蚀斑。利用烧蚀面积与激光脉冲能量的关系确定SiC的烧蚀阈值。给出了SiC样品的烧蚀阈值与飞秒激光波长的依赖关系。实验结果表明,可见光区随波长增加,烧蚀阈值从0.29J/cm2增加到0.67J/cm2;而在近红外区,SiC的烧蚀阈值为0.70J/cm2左右,基本上不随激光波长变化而改变。结合计算结果,可以认为在飞秒激光烧蚀SiC的过程中,在近红外区,光致电离和碰撞电离均起到了重要的作用;而在可见光区,光致电离的作用相对大一些。

Visible-Infrared Femtosecond Laser-Induced Optical Breakdown of 6H SiC

To study the damage mechanism and micromachining of 6H SiC, the femtosecond (fs) laser pulse is focused on the front of the sample by a 10× microscope objective lens. The ablation pits are measured with scanning electron microscope (SEM) and optical microscope (OM). The experimental results indicate that high quality micro-structures can be fabricated in SiC crystal. Based on the dependence of ablation area on laser pulse energy, the threshold fluence is determined accurately, and the wavelength dependence of SiC ablation threshold fluence is given. The threshold fluence of SiC is found to increase with the incident laser wavelength from 0.29 J/cm2 to 0.67 J/cm2 in the visible region, while it remains almost constant (about 0.70 J/cm2) for NIR laser. For the NIR laser pulses, both photoionization and impact ionization play important role in electronic excitation, while for viaible lasers, photoionization is dominant.