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Results on copper metallization diffusion barriers using high-entropy alloy (HEA) nitride are reported. The HEA nitride (Al Mo Nb Si Ta Ti V Zr) 50 N 50 is amorphous in the as-deposited state and remains its noncrystallinity up to a high temperature of 850 C⁠. To evaluate its diffusion barrier characteristics, Cu∕(Al Mo Nb Si Ta Ti V Zr) 50 N 50∕ Si test structures were prepared and annealed under 750–900 C for 30 min⁠. The results show that the current nitride prevents the reaction between Cu and Si before its failure at 900 C⁠. The outstanding barrier performance and high thermal stability of amorphous structure are suggested to originate from multiprincipal-element effects.