Silicon carbide (SiC) exhibits excellent properties, such as high breakdown field strength, high saturation electron drift velocity, high thermal conductivity, and good chemical stability. These characteristics enable miniaturization and weight reduction of power modules, ushering in a new era for power devices. Having successfully transitioned from R&D to mass production, SiC materials and devices have advanced rapidly through industrial scaling. However, the price of contemporary SiC power devices is 2?3 times higher than that of their silicon-based equivalents with comparable specifications. This cost differential partially constrains the further market penetration of SiC technology. For the SiC industry, reducing costs while enhancing efficiency is a critical priority for the next developmental phase. The current mainstream wafer diameter of SiC is 6?8 inch. Transitioning from 8-inch to 12-inch substrates delivers over 125% greater usable area, substantially increasing the die yield per wafer by more than two-fold. Recent emerging applications such as augmented reality (AR) glasses and advanced integrated circuit (IC) packaging have further accelerated the market demand for 12-inch SiC substrates. However, as the crystal diameter increases, the manufacturing complexity increases exponentially. The principal challenges in fabricating 12-inch 4H-SiC crystals include the development of high-quality 4H-SiC seeds, nonuniform thermal field distribution, nucleation control exacerbated by superscaled dimensions, inefficient vapor-phase mass transport, evolution dynamics of precursor species in supersized growth systems, and intensified thermal stress leading to crystal cracking and defect propagation. This study aims to achieve an efficient diameter expansion of seeds in fabricating 12-inch n-type 4H-SiC substrates and characterize their properties.

Utilizing a home-grown 8-inch (0001) carbon-face 4H-SiC seed crystal with a 4° off-orientation toward 112ˉ0, diameter expansion was achieved via the physical vapor transport (PVT) method. The thermal fields during 12-inch SiC crystal growth and diameter expansion were investigated using the Virtual Reactor simulation software. To expand the diameter of the crystals from 8 inch to 12 inch, a “trapezoidal” temperature field was designed and constructed with a small radial temperature gradient at the center and a large radial temperature gradient only within a certain range of the edges. This ensured expansion of the edges while reducing the overall stress on the crystal. To optimize the quality of the 12-inch crystals, a continuous flat temperature field was designed and constructed in conjunction with large-diameter seeds (>300 mm), without the need for diameter expansion, to optimize and improve the quality of the 12-inch seed. Following the acquisition of high-quality 12-inch seed, n-type 4H-SiC single crystals were grown under a controlled nitrogen gas flow. The as-grown boules were subjected to cylindrical grinding and end-facing to meet the standardized 12-inch diameter specification. These boules were sliced using laser cutting. The resulting wafers were subsequently thinned, polished, and cleaned to produce 12-inch n-type 4H-SiC substrates. The wafers were characterized by Raman spectroscopy, contactless resistivity measurement, automatic microscope scanning, high-resolution X-ray diffraction (HRXRD), and dislocation detection to analyze their polytype, micropipes, resistivity, crystal quality, and dislocations.

Building on our previously established 8-inch high-efficiency diameter expansion technology, this research leveraged a home-grown 12-inch SiC single-crystal furnace. Concurrently, numerical simulations and crystal growth experiments were employed to investigate the diameter expansion mechanism of ultra-large SiC single crystals. To balance the single-step diameter expansion magnitude and thermal stress compatibility in ultralarge single crystals, we engineered tailored thermal field profiles, flow field configurations, and diameter expansion hardware. Commencing with 8-inch SiC seeds, iterative crystal growth and processing cycles progressively scaled the crystal diameter to 12 inch. After achieving the diameter, multi-cycle crystal growth and processing optimized the crystalline quality in the expansion zone, ultimately enhancing the 12-inch seed integrity. Following the acquisition of high-quality 12-inch seeds, nitrogen gas doping was precisely regulated to achieve a 12-inch n-type conductive 4H-SiC ingot. A 12-inch n-type 4H-SiC substrate with a thickness of 560 μm was obtained through laser cutting processing. The performance of the 12-inch SiC substrate was characterized. Raman mapping indicated that there were no polymorphic inclusions, such as 6H and 15R, and the area ratio of the 4H polytype reached 100%. The micropipe distribution map indicated that there was no proliferation of micropipes in the edge expansion area, and the micropipe density was less than 0.01 cm^-2. The resistivity distribution map showed a resistivity range of 20.5?23.6 mΩ·cm, with an inhomogeneity of less than 2%. The 5-point rocking curves of the (004) diffraction plane exhibited nearly symmetrical single peaks without multiple peaks, indicating that there were no small-angle grain boundary defects in the substrate. The average full-width half maximum of the 5-point rocking curve was 20.8″, which indicates good crystalline quality. Threading screw dislocation (TSD) density was 2 cm^-2 using molten KOH corrosion.

The 12-inch 4H-SiC seed was obtained by the PVT method, expanding the boule diameter from 8 inch to 12 inch to obtain home-grown conductivity type 4H-SiC crystals. The 12-inch n-type 4H-SiC substrate with a thickness of 560 μm was processed through standard semiconductor processing steps including laser cutting, grinding, and polishing. The polytype of the entire wafer was 4H without other polytype inclusions. The micropipe density was less than 0.01 cm^-2. The resistivity range was 20.5?23.6 mΩ·cm, with an average value of 22.8 mΩ·cm. The full-width half maximum (FWHM) of the rocking curve of the (004) diffraction peak was 20.8″. The TSD density was 2 cm^-2. These results indicate the high quality of the 12-inch n-type 4H-SiC substrate. Further research is required to control the dislocation density in 12-inch SiC crystals and precise chemical-mechanical polishing process of the substrates.