| dc.description.abstract | Silicon carbide (SiC) is a key material for third-generation semiconductors. Compared to the most widely used silicon wafers, SiC exhibits superior physical properties and chemical stability. Its higher thermal conductivity and wider bandgap provide it advantages in high-power and high-frequency devices. However, the manufacturing cost of SiC wafers has remained high due to two main challenges: (1) the difficulty and time-consuming nature of the initial SiC crystal growth process, resulting in limited availability of high-quality and large-volume ingots; and (2) the time-consuming and energy-intensive processes in the later stages of edge trimming, slicing, grinding, and polishing. These bottlenecks have kept the production costs of SiC wafers consistently high, posing a critical challenge for the SiC wafer manufacturing industry. The development of technologies for wafer thinning and more efficient cutting, grinding, and polishing processes has become a proactive research direction for SiC wafer manufacturers in response to the high material costs. Among these, the ultrafast laser stealth slicing technology enables the cutting of thinner wafers while minimizing surface material damage. Thinning wafers significantly increase material utilization, and reduced surface damage effectively lowers the time and consumables required for subsequent grinding and polishing processes.
Experimental findings indicate that with a pulse energy (E_p) of 8.56 µJ and a pulse overlap (OP) of 70.8%, a stable and uniform single modified layer is achievable, forming at the expected laser focus plane. Remarkably, under the same pulse energy, an increase in pulse overlap to OP = 85.4% led to the discovery that not only a single modified layer was formed at the original focus plane but also a second modified layer above it (along the direction of incident light), resulting in the simultaneous creation of a double modified layer. The study further notes that this phenomenon can be replicated within specific ranges of laser processing parameters. Moreover, alterations to the laser parameters were observed to cause variations in the distance between these two modified layers.
Regarding the formation of this second modified layer, this study proposes its formation mechanism, suggesting that it is due to the increase in pulse frequency. The non-linear change in absorption coefficient caused by the cumulative temperature rise along the path of incident light is believed to be the cause. Therefore, when the laser energy density at the non-focal plane position reaches the threshold for SiC modification, the second modified layer can be formed. Consequently, its origin is different from the ＂Laser filamentation＂ phenomenon, and this mechanism has been experimentally validated in this study. Based on this mechanism, variations in the pulse energy of the laser can change the distance between these double modified layers. The study also experimentally verifies that as the laser pulse energy increases, the distance between these two layers also increases. Through grinding and etching of the cross-sectional surface, this study further observes the structure of these two modified layers. Under the current studied parameters, although the second modified layer is not at the focal plane, its modified range is greater than that of the first modified layer at the focal plane.
In practical applications, the technology of simultaneously forming double modified layers not only doubles the efficiency of SiC slicing but also allows for the direct achievement of SiC wafer slices with a thickness of less than 100 µm. | en_US |