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The manufacturing process of superconducting quantum processor chips faces unique metal contamination challenges, with significant differences in material systems and process characteristics compared to traditional semiconductor chips. This study focuses on the issue of metal contamination in the fabrication process of quantum chips, systematically analyzing the sources, diffusion mechanisms, and prevention strategies of metal contamination in quantum chips. It particularly emphasizes the bulk diffusion and surface migration behaviors of superconducting materials (such as Ta, Nb, Al, TiN) on sapphire and silicon substrates. The aim is to provide theoretical basis and technical references for process optimization, and to promote the industrialization process of quantum computing technology in our country.
The metal contamination in the fabrication of quantum chips is mainly caused by the metal film materials used in the process, the external environment, or the unintended metal impurity atoms introduced during the manufacturing process. Among them, some quantum chip components directly use superconducting metal materials. Unlike semiconductor chips, they cannot achieve front and back stage isolation, resulting in the continuous presence of metal surface migration channels, and there are exposed metal structures on the chip surface. Metal contamination often leads to two fundamental failure problems: circuit short circuits and leakage currents. These problems mainly result from the bulk diffusion of metal impurities in the dielectric layer and the migration behavior on the sample surface. The diffusion and migration rates of metals are affected by temperature, interface reactions, defects, and grain boundaries. The results show that the sapphire substrate, due to its dense lattice structure, exhibits excellent anti-diffusion performance, reducing the risk of contamination and providing a stable interface environment for superconducting quantum chips. For silicon substrates, special attention needs to be paid to the contamination risks posed by high-mobility metals such as Au, In, and Sn. Experimental verification shows that Ti/Au under bump metallization structures on silicon substrates are prone to Au penetration diffusion, and increasing Ti thickness does not significantly improve the blocking effect. The low-temperature process (<250 °C) and ultra-low-temperature operating environment (mK level) of quantum chips effectively suppress metal diffusion, but exposed metal surfaces and material diversity still pose unique challenges.
The study recommends establishing a dedicated metal contamination prevention system for quantum chips and proposes future research directions, including evaluation of novel materials, surface state regulation, and long-term reliability studies. This work provides important theoretical support and technical guidance for process optimization and performance enhancement of superconducting quantum chips.-
Keywords:
- superconducting quantum processor chip /
- process line metal contamination /
- bulk diffusion /
- surface migration
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