Surface micromorphology and nanostructures evolution in hybrid laser processes of slicing and polishing single crystal 4H-SiC

Abstract

Slicing and post-treatment of SiC crystals have been a significant challenge in the integrated circuit and microelectronics industry. To compete with wire-sawing and mechanical grinding technology, a promising approach combining laser slicing and laser polishing technologies has been innovatively applied to increase utilization and decrease damage defects for single crystal 4H-SiC. Significant material utilization has been achieved in the hybrid laser processes, where material loss is reduced by 75% compared to that of conventional machining technologies. Without any special process control or additional treatment, an internally modified layer formed by laser slicing can easily separate the 4H-SiC crystals using an external force of about ∼3.6 MPa. The modified layer has been characterized using a micro-Raman method to determine residual stress. The sliced surface exhibits a combination of smooth and coarse appearances around the fluvial morphology, with an average surface roughness of over S_a 0.89 µm. An amorphous phase surrounds the SiC substrate, with two dimensions of lattice spacing, d = 0.261 nm and d = 0.265 nm, confirmed by high-resolution transmission electron microscopy (HRTEM). The creation of laser-induced periodic surface nanostructures in the laser-polished surface results in a flatter surface with an average roughness of less than S_a 0.22 µm. Due to the extreme cooling rates and multiple thermal cycles, dissociation of Si-C bonding, and phase separation are identified on the laser-polished surface, which is much better than that of the machining surface. We anticipate that this approach will be applicable to other high-value crystals and will have promising viability in the aerospace and semiconductor industries.