Crystal cleavage, periodic nanostructure and surface modification of SiC ablated by femtosecond laser in different media

SiC, as one typical 3rd generation semiconductor, has high potential to be used as the substrate for harsh environment sensors. However, the etching of this material is still challenging. Femtosecond laser has been demonstrated to have great potential in SiC etching, but the material removal mechanisms need further investigation. Herein, the two-temperature model considering carrier concentration is utilized to illustrate the microscopic mechanism of carrier concentration and temperature change in SiC caused by femtosecond laser irradiation. An 800 nm, 50 fs, 10 Hz Ti: sapphire femtosecond laser was used to process SiC in different media including air, HF and water. The ablation threshold of SiC in the three media is calculated. The highest ablation threshold (4.98 J/cm2) is obtained when the pulse number N = 50, in air. The lowest ablation threshold (0.53 J/cm2) is obtained when the pulse number N = 300, in HF. Results indicate that ablation threshold is strongly dependent on the laser pulse number and processing medium. Based on the cleavage phenomenon of SiC crystal structure observed by micro-nano characterization, the mechanism model of femtosecond laser-induced periodic structure of SiC surface based on material lattice cleavage is established, and the relationship between the intrinsic texture and the evolution of periodic structure of ablation surface is revealed. This will provide a new way to understand the ablation mechanism of femtosecond laser. In addition, the processing media has significant effect on surface roughness and chemical bond characteristics of SiC. Liquid processing media can reduce the surface roughness and avoid oxidation, which is helpful to manufacture SiC devices with specific surface requirements using femtosecond laser as an auxiliary method.