The growing demand for high-performance power electronics and wide-bandgap semiconductor devices has accelerated the need for large-diameter silicon carbide (SiC) substrates, particularly 12 inch wafers. Silicon carbide—endowed with exceptional thermal conductivity, a wide bandgap, and a high breakdown electric field—is a prime candidate for next-generation high-temperature, high-frequency, and high-power devices. However, SiC’s intrinsic properties (i.e., high hardness, brittleness, and low fracture toughness) pose substantial challenges to conventional wire-saw slicing methods, which suffer from low material yield, slow processing rates, and surface damage. More critically, traditional techniques struggle to meet the mechanical and geometric tolerances required for 12 inch wafers. Consequently, developing an efficient, low-damage, and scalable slicing technology for large-diameter SiC crystals has become a pressing priority. In response, laser slicing technology—especially ultrafast laser-induced internal modification—offers a promising alternative. Nevertheless, implementing this method on 12 inch SiC ingots introduces new challenges, including increased stress, warpage, and inhomogeneities across the larger crystal volume. This study aims to address these issues by integrating real-time focal correction, spherical aberration pre-compensation, and ultrasonic delamination to achieve high-quality slicing of 12 inch n-type 4H-SiC wafers.

The experimental substrate was a 12 inch (300 mm) diameter n-type 4H-SiC single crystal grown via the physical vapor transport (PVT) technique. The crystal had a thickness of 12 mm and was preprocessed using a dual-surface polishing method, resulting in a total thickness variation (TTV) of 17 μm and a surface roughness below 3 nm. A custom-built laser slicing system was employed, featuring a linearly polarized picosecond laser source with a wavelength of 1030 nm, a pulse width of 15 ps, a maximum power of 40 W, and an adjustable repetition rate of 100?500 kHz. The laser beam was expanded and focused using a high-numerical-aperture (0.67) objective lens with a working distance of 9.5 mm. To mitigate the significant refractive index mismatch between air (n≈1.0) and SiC (n≈2.6), a depth-dependent spherical aberration pre-compensation strategy was implemented using a spatial light modulator (SLM). The compensation phase maps were designed to optimize the focal spot size and reduce energy dispersion within the crystal volume. Real-time focal tracking was performed using a color confocal displacement sensor, which provided dynamic feedback to adjust the z-axis height via a piezoelectric actuator, synchronized with the surface topography. The optimized laser parameters were as follows: 5 W power, 100 kHz repetition frequency, 400 mm/s scanning speed, 200 μm inter-line pitch, and a target focus depth of 230 μm—resulting in a final modified layer at a depth of 680 μm. After laser processing, the ingot was immersed in deionized water, and ultrasonic waves (20?50 kHz) were applied to induce wafer delamination.

The sliced 12 inch wafers were characterized for geometry, uniformity, and surface quality. The resulting wafers exhibited a TTV of less than 10 μm—representing a significant improvement over conventional techniques. The bow value was -14.07 μm, indicating a concave profile with stress concentration consistent with the scanning direction. Profilometry results revealed minimal height deviation along the laser scanning axis (0° direction), suggesting that focal correction effectively minimized depth fluctuations during internal processing. In contrast, larger deviations were observed in the feed direction (90°), attributed to cumulative stress effects between adjacent laser lines. White light interferometry (Sensofar S Neox) was used to analyze surface morphology at multiple wafer locations (center, edge, and facet) (Fig. 10). The central region (A) displayed uniform sawtooth structures with no evidence of interlayer delamination. By comparison, the wafer facet (B) exhibited minor structural irregularities, likely due to local refractive index variations and the need for dedicated compensation at the wafer edges. Regions C?F (edges) showed well-formed periodic crack arrays, reflecting stable energy distribution and laser?material interaction. The measured surface roughness (S_a) ranged from 3.25 μm to 3.93 μm, with the lowest values near the center (A) and slightly higher values at the edges (Table 1). Average step heights remained below 16 μm across all regions. The observed sawtooth and step structures resulted from localized thermal stress-induced cracking along the (0001) crystal plane—initiated by laser modification and propagated uniformly during ultrasonic delamination. These results highlight the importance of depth control and focal optimization for achieving uniform slicing outcomes. Simulation results further confirmed that an optimal processing depth of 230 μm yielded the shortest focal spot length (84 μm), minimizing kerf depth and reducing the need for post-slicing grinding (Figs. 4?5). When the preset and actual focal depths diverged by more than -20 or 20 μm, depth deviation increased dramatically, leading to potential slicing failure or multilayer separation.

This study reports the first successful slicing of 12 inch n-type 4H-SiC crystals using a combination of picosecond laser-induced internal modification and ultrasonic delamination. By implementing spherical aberration pre-compensation and real-time focal correction, high-precision laser slicing was achieved, producing wafers with a thickness of 680 μm, TTV<10 μm, and bow of -14.07 μm. The resulting wafers exhibited excellent surface uniformity, with S_a values between 3.25 and 3.93 μm and step heights below 16 μm. These findings confirm the feasibility of scalable laser slicing for large-diameter SiC substrates and provide key insights into laser?crystal interactions, laying a solid foundation for future industrial-scale wafering processes. The proposed methodology represents a significant advancement toward the efficient, high-yield manufacturing of next-generation SiC-based power devices.