Fabrication of few-micron-thick modified layers in 4H-SiC: Multi-pulse-driven transition from nanodeformation to decomposition via the optical near-field enhancement effect

The femtosecond laser (fs-laser) slicing technique, owing to its superior efficiency and reduced loss, is anticipated to supplant wire sawing as the predominant method for slicing silicon carbide (SiC). Nevertheless, the current ultrashort laser slicing techniques are focused on a combination of high laser fluence, exceeding the laser ablation threshold, and a sub-micron depth of field attributable to the objective lens, leading to thicker modified layers. This paper introduces an innovative way for producing a thinner modified layer in 4H-SiC, transitioning from nanodeformation to decomposition. To begin with, experimental results demonstrate that nanodeformation persists in laser-treated regions and can achieve decomposition via the optical near-field enhancement effect. Surface decomposition can be divided into four stages: nanoholes, LSFL, HSFL, and deep pits. In addition, the lower laser fluences, which facilitate the creation of nanoholes and nano-ripples, are appropriate for the generation of modified layers in 4H-SiC. The new method offers the advantages of a thinner deformation zone and fewer defects. On this basis, a modified zone of 7.34 μm is created at a depth of 200 μm under the surface of 4H-SiC using a lens with a 30 mm focal length. Notably, the thickness of the modified layer could be controlled to 2.90 μm, with negligible stress-affected areas around the modified layer. It is worth noting that the modified layers fabricated by reducing the laser fluence have the dual effect of making the modified unit thinner and improving spatial consistency to a significant degree. This novel technique for producing modified layers in SiC can independently enhance accuracy and is also applicable to laser processing with cylindrical lenses, significantly improving the efficiency of the laser slicing technique.