Scanning direction dependence on crystal orientations of a femtosecond laser-assisted 4H-SiC wafer slicing

4H silicon carbide (4H-SiC) is one of the promising semiconductor materials due to its wide bandgap, high thermal conductivity, and high breakdown electric field strength. Its superior mechanical characteristics ensure reliable performance in extreme environments such as automotive, energy production, and aerospace. However, a traditional wafer production method that uses a diamond wire saw is ineffective due to the high hardness and brittleness of 4H-SiC. Recently, a pulsed laser-assisted process, including ns-, ps-, and fs-pulses has been applied to wafer slicing. Among different pulse widths, femtosecond laser-assisted wafer slicing technology can minimize the heat-affected zone without material loss and debris creation during the process. Besides considering pulse width for effective wafer slicing, it is crucial to consider the laser scanning direction to improve production capacity and maintain the quality of the sliced wafer surface because the biased crack propagation induces surface morphology variation and mitigates peeling stress in layer separation. Here, a femtosecond laser-assisted wafer slicing for 4H-SiC was performed to evaluate the modified surface morphology according to the laser scanning direction and processing sequence. Slicing with the laser scanning direction was investigated in relation to the crystal orientation. Although the average surface roughness is within 1 to 2 $\mu$m, tensile stress for layer separation can be decreased down to 4.22$\pm$0.60 MPa depending on the laser scanning direction, while in some cases exceeding the upper limit of 38 MPa of the tensile test machine. The effect of the crack propagation region differs from the laser scanning direction and processing sequence despite the identical line interval condition for laser slicing. The interval between lines generates 6.65 to 3.55 $\mu$m for the separable layers, which requires tensile stress that can be regulated from 18.1 to 3.8 MPa while improving surface roughness. Laser slicing, as a result, considering scanning direction and processing sequence induces different crack propagation patterns. Considering the crystal orientation during the wafer slicing is important to improve production efficiency and maintain wafer quality.