Silicon carbide has a Mohs hardness of 9.2–9.5, second only to diamond. It is highly brittle and has low fracture toughness, while also offering excellent high-temperature resistance, corrosion resistance, and radiation resistance. However, it is difficult and costly to process, requiring multiple steps such as cutting, lift-off, etching, and polishing. Processing quality directly affects the conduction loss, withstand voltage level, and service life of power devices. Currently, wire cutting is widely used because of its low cost, simple equipment structure, and suitability for mass production, and diamond cutting tools are also relatively easy to obtain. However, wire cutting causes substantial material loss and has extremely low processing efficiency.
Material Loss Caused by Wire Cutting
During wire cutting, the high-speed movement of the cutting wire not only produces kerf loss with a kerf width equal to the wire diameter; because the wafer surface prepared by wire cutting is very rough, subsequent grinding and polishing and other finishing processes are also required. Ultimately, cumulative material loss can reach 30%–50% of the total raw material. The multi-wire sawing process also requires solutions to cool the kerf and clean debris, generating large amounts of silicon-containing waste liquid. The micro/nano-scale particles in it are difficult to flocculate and hard to recycle, causing significant environmental impact.
Laser Lift-Off: Performing an "Invisible Surgery" Inside the Crystal
Laser lift-off is an important process for SiC slicing and belongs to internal modification and layer-splitting processing technology. Its core principle is laser internal focusing modification plus external-force splitting separation.
Schematic diagram of SiC crystal laser lift-off technology
The first stage is internal modification. Using the ultrahigh penetration and focusing characteristics of ultrashort-pulse lasers, the laser focus is precisely controlled by an optical path and focused at a preset depth inside the silicon carbide wafer. After high-energy laser focusing inside the wafer, local silicon carbide material undergoes lattice distortion, phase transformation, and microcrack propagation, forming a continuous, uniform modified layer. The mechanical strength of the modified layer is greatly lower than that of the substrate material, and there are no processing marks on the surface, realizing invisible modification. The second stage is splitting separation. Through mechanical micro-tension, gas blowing, or tensile external force, the wafer is precisely separated along the internal modified layer, completing lossless cutting and separation of the entire wafer.
Unlike traditional wire cutting, non-contact laser lift-off technology can effectively avoid problems such as cutting tool wear and SiC wafer failure caused by mechanical stress, thereby achieving high-quality and high-precision lift-off. Laser lift-off technology significantly improves the processing efficiency and quality of silicon carbide wafers and reduces the manufacturing cost of silicon carbide substrates. It has prominent advantages of high production efficiency and low material loss. Laser lift-off has a very small modified layer thickness, which can significantly improve material utilization during silicon carbide wafer preparation. Achieving high-quality and high-efficiency lift-off on silicon carbide wafers is expected to break through technical bottlenecks and high-cost constraints, and promote market applications in which silicon carbide devices replace silicon substrates. The environmental effects of laser lift-off technology are also significant. In traditional cutting processes, the problems of cutting fluid and dust pollution are relatively serious, while laser lift-off, as a non-contact process, can reduce industrial waste emissions. Combined with the efficient performance of silicon carbide devices in energy conversion, this technology helps global carbon neutrality goals from both the manufacturing and application ends.
Global Race: Current Status of Laser Lift-Off Technology Development
Silicon carbide wafers are developing toward larger sizes, and laser lift-off cutting technology has been widely promoted. Laser wavelength, pulse energy, focusing depth, and scanning spacing are the core parameters that determine the continuity and uniformity of the modified layer. 532 nm and 1064 nm ultrafast lasers have excellent penetration into silicon carbide, and the focused spot is smaller. The modified layer thickness can be precisely controlled at 10–30 μm, and modified cracks propagate in a directed manner without diffusing into the device functional area. Through dynamic polarization control and beam shaping technology, the morphology of the modified layer can be optimized, cutting flatness can be improved, and wafer splitting warpage can be effectively suppressed. Domestic research focuses on batch processing consistency for large-size wafers, low-stress cutting of ultra-thin wafers (50–100 μm), and optimization of narrow-spacing die cutting technology. Fully automated laser lift-off cutting of 8-inch silicon carbide wafers has been achieved. Under optimized process conditions, the cutting street width can be reduced to within 20 μm, the die yield exceeds 98%, and single-wafer processing efficiency is increased by more than 30% compared with traditional processes, solving the problem that traditional single modification cannot adapt to thick wafer processing. Source: Shuoke Crystal.
In crystal lift-off technology, as early as 1985, American scientists demonstrated that thin layers could be lifted off from Si and GaAs wafers under the action of residual tensile stress in a stress layer. However, early crystal lift-off experimental processes were difficult to control because when the stress reached the threshold determined by the wafer fracture toughness, cracks would spontaneously generate and propagate randomly, causing uneven lift-off layer thickness or even fragmentation.
IBM developed a controlled lift-off technology. This method designs an additional traction layer to apply external force to trigger fracture and directionally guide crack propagation, and also establishes a theoretical model for the correlation between critical stress and spalling layer thickness, providing guidance for process optimization. In addition, wafer-level Si, GaN single crystals, as well as III-V solar cells, integrated circuits, LEDs, and other semiconductor devices, can all use this technology to achieve controlled lift-off.
In terms of industrialization technology, Germany's Siltectra cold split technology and Japan's Disco laser modification process can control SiC slicing material loss to within 60 μm and have achieved 8-inch wafer mass production; European and American manufacturers monopolize UV excimer light sources and have long dominated the interface lift-off equipment market for Micro-LED epitaxial wafers.
In recent years, domestic progress has been significant. Research teams from Huazhong University of Science and Technology and CETC have overcome SiC internal modification and crack directional control technology. Enterprises such as Han's Laser and HGTECH have achieved localization of UV laser lift-off equipment, and domestic equipment has entered verification in LED and power device production lines. At present, domestic 6-inch SiC lift-off process indicators are close to international levels, but the energy uniformity of 8-inch large-size full wafers is relatively poor, and the crack deviation problem of N-type silicon carbide has not been completely solved. High-power UV lasers and high-precision optical modules still rely on imports.