High-precision laser slicing of silicon carbide using temporally shaped ultrafast pulses

The advent of laser-assisted methods for material slicing attracts a particular attention for technologically important materials as silicon carbide (SiC). Using femtosecond lasers, one can locally initiate multiphoton ionization inside SiC, leading to internal material modifications for slicing SiC ingots into individual wafers. However, intense focused light inside SiC suffers from strong nonlinear effects, such as plasma shielding and self-focusing, which limit energy localization and affect the quality of internal modifications. In this research, we employ temporally-shaped ultrafast trains of pulses for semi-insulating SiC crystal modification. These are generated through an engineered stack of birefringent crystals and permitted successfully slicing a SiC wafer. By adjusting laser parameters, we demonstrate improved energy deposition near the laser focal point and find an optimal combination of laser energy (total energy of pulse train: 10μJ) and number of sub-pulses (8 sub-pulses) to achieve thin single-layer modifications and cracks (thickness: 16.5μm). The suppression of pre-focal plasma shielding and improved control for energy deposition inside crystals are confirmed by side-view luminescence microscopy. Ultimately, the benefits from the technique allow a reduction of the modification layer down to 16.5μm, corresponding to an important advancement for low material-loss SiC wafer slicing.