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Silicon carbide (SiC) is widely used in many research fields because of its excellent properties. The femtosecond laser has been proven to be an effective method for achieving high-quality and high-efficiency SiC micromachining. In this article, the ablation mechanism irradiated on different surfaces of 6H-SiC by a single pulse under different energies was investigated. The changes in material elements and the geometric spatial distribution of the ablation pit were analyzed using micro-Raman spectroscopy, Energy Dispersive Spectrum (EDS), and an optical microscope, respectively. Moreover, the thresholds for structural transformation and modification zones of 6H-SiC on different surfaces were calculated based on the diameter of the ablation pits created by a femtosecond laser at different single-pulse energies. Experimental results show that the transformation thresholds of the Si surface and the C surface are 5.60 J/cm2 and 6.40 J/cm2, corresponding to the modification thresholds of 2.26 J/cm2 and 2.42 J/cm2, respectively. The Raman and EDS results reveal that there are no phase transformations or material changes on different surfaces of 6H-SiC at low energy, however, decomposition and oxidation occur and then accumulate into dense new phase material under high-energy laser irradiation. We found that the distribution of structural phase transformation is uneven from the center of the spot to the edge. The content of this research reveals the internal evolution mechanism of high-quality laser processing of hard material 6H-SiC. We expect that this research will contribute to the further development of SiC-based MEMS devices. [ABSTRACT FROM AUTHOR]

• The morphology and structural transformation of 6H-SiC under irradiation of single pulse with varying energies was investigated. Three distinct modification regimes were identified based on pulse energy. • At low pulse energies just above the modification threshold, the sample surface undergoes moderate modification, no larger craters and amorphous silicon are produced. At even higher energies, nonlinear absorption and ionization occur under ultrafast laser irradiation, Si-C crystal bonds are broken and melting, resolidification and the generation of amorphous and crystalline silicon phase appeared. • Tunneling ionization and avalanche ionization are responsible for the generation of free electrons in SiC sample and melting/resolidification happens when a large portion of energy is transferred from electrons to the lattice. Silicon carbide (SiC) is promising in semiconductor devices operating in extreme environments owing to its excellent properties including wide forbidden band, high thermal conductivity, thermal stability, chemical inertness, and high saturation rate. However, its Mohs hardness of 9 poses challenges for conventional machining techniques. Femtosecond laser processing offers an effective alternative for SiC processing, yet the underlying mechanism of interaction between laser pulse and SiC remains unclear. Herein we studied the mechanism of laser interacted with SiC, thoroughly investigated the structural transformation and morphology change of single crystal 6H-SiC induced by single ultrafast laser pulse irradiation at different pulse energies. The morphology changes of single pulse induced crater, i.e., diameter and depth, are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The structural transformation and changes in the chemical composition are analyzed using micro-Raman spectroscopy. Moreover, the evolution of lattice arrangement is revealed by high-resolution transmission electron microscopy (TEM). At low pulse energies just above the modification threshold, the sample surface undergoes moderate modification, no larger craters and amorphous silicon are produced. At even higher energies, nonlinear absorption and ionization occur under ultrafast laser irradiation, the energy of the hot free electrons is transferred to the cold crystal lattice through electron–phonon scattering, causing a sharp increase in the lattice temperature. Si-C crystal bonds are broken and melting, resolidification and the generation of amorphous and crystalline silicon phase appeared. [ABSTRACT FROM AUTHOR]