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Low-Defect Ni/Ti Composite Backside Ohmic Contact for Thinned 4H-SiC Devices Formed by 355 Nm UV Laser Annealing
Abstract:
The formation of high-quality ohmic contacts on the backside of thinned SiC wafers is critical for vertical power devices to minimize specific on-resistance and enhance energy efficiency. Conventional green laser (532 nm) annealing for Ni-based backside metallization faces challenges such as severe carbon out-diffusion, interfacial voids, and high contact resistivity. This work introduces a Ni/Ti composite metallization scheme combined with 355 nm ultraviolet laser annealing (UV-LA) to address these limitations. By replacing the Ni single-layer with a Ni/Ti stack layer, the reflectivity at 355 nm UV laser annealing is reduced, enabling efficient energy absorption and localized alloying. Ti acts as a diffusion barrier, suppressing Kirkendall void formation and immobilizing carbon through in-situ TiC formation, as confirmed by XRD analyses. Additionally, UV-LA at 4.2 J/cm² with Ni/Ti composite metallization optimizes reaction kinetics, achieving a 69% reduction in void density and a 65% improvement in alloy layer flatness compared to Ni alloy layer. The results validate Ni/Ti-UV-LA as a scalable solution for high-reliability SiC backside metallization, paving the way for next-generation power devices.
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March 2026
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