Slicing of 4H-SiC Wafers Combining Ultrafast Laser Irradiation and Bandgap-Selective Photo-Electrochemical Exfoliation

Abstract

High-efficiency and low-loss processing is the mainstay to reduce the cost and deepen the application of 4H silicon carbide (4H-SiC) wafers in high-power and high-frequency electronics. In this study, the high-yield slicing of 4H-SiC wafers is realized by combining femtosecond laser irradiation and bandgap-selective photo-electrochemical (PEC) exfoliation. By combining light-absorption measurements, micro-Raman, and micro-photoluminescence characterizations, it is found that the damage layer formed inside 4H-SiC after femtosecond-laser irradiation consists of amorphous silicon and amorphous carbon. This indicates that the femtosecond-laser irradiation leads to phase separation in 4H-SiC. The bandgap of the damage layer is 0.4 eV. Taking advantage of the different bandgap energies of the damage layer and the perfect 4H-SiC region, the damage layer is removed from the perfect region of 4H-SiC by using bandgap-selective PEC etching. During the PEC etching, light-generated holes can selectively oxidize and corrode the damaged layer with the assistance of the HF solution, and leave the upper and lower perfect 4H-SiC layers being intact. The current work contributes to the development of the high-yield and high-throughput femtosecond laser slicing of 4H-SiC wafers.