Gallium nitride wafer slicing by a sub-nanosecond laser: effect of pulse energy and laser shot spacing

Gallium nitride (GaN)-based devices surpass the traditional silicon-based power devices in terms of higher breakdown voltage, faster-switching speed, higher thermal conductivity, and lower on-resistance. However, heteroepitaxial GaN growths like GaN on sapphire are not suitable for power devices due to the threading dislocation densities as high as 10(8)/cm(2). Recently, homoepitaxial GaN growth has become possible thanks to the native GaN substrates with dislocation densities in the order of 10(4)/cm(2) but the extremely high cost of the GaN substrates makes the homoepitaxy method unacceptable for industrial applications, and the slicing of wafers for reusing them is an effective solution for cost reduction. In this study, we will investigate a route for slicing the GaN single crystal substrate by controlling the laser pulse energy and changing the distance between each laser shot. The 2D and 3D crack propagations are observed by a multiphoton confocal microscope, and the cross section of samples is observed by a scanning electron microscope (SEM). The results showed that two types of radial and lateral cracking occurred depending on the pulse energy and shot pitch, and controlling them was of importance for attaining a smooth GaN substrate slicing. Cross-sectional SEM images showed that at suitable pulse energy and distance, crack propagation could be controlled with respect to the irradiation plane.

Automated summary

The study investigates a method for slicing GaN single crystal substrate by controlling laser pulse energy and changing the distance between each laser shot. The results show that different types of cracking occur depending on the pulse energy and shot pitch, and controlling them is crucial for achieving smooth GaN substrate slicing. SEM images indicate that crack propagation can be controlled with respect to the irradiation plane at suitable pulse energy and distance.