Tantalum-based diffusion barriers in Si/Cu VLSI metallizations

We have studied sputter-deposited Ta, Ta₃₆Si₁₄, and Ta₃₆Si₁₄N₅₀ thin films as diffusion barriers between Cu overlayers and Si substrates. Electrical measurements on Si n ⁺p shallow junction diodes demonstrate that a 180-nm-thick Ta film is not an effective diffusion barrier. For the standard test of 30-min annealing in vacuum applied in the present study, the Ta barrier fails after annealing at 500 °C. An amorphous Ta₇₄Si₂₆ thin film improves the performance by raising the failure temperature of a 〈Si〉/Ta ₇₄Si₂₆(100 nm)/Cu(500 nm) metallization to 650 °C. Unparalled results are obtained with an amorphous ternary Ta₃₆Si ₁₄N₅₀ thin film in the Si/Ta₃₆Si ₁₄N₅₀(120 nm)/Cu(500 nm) and in the Si/TiSi₂(30 nm)/Ta₃₆SiN₅₀(80 nm)/Cu(500 nm) metallization that break down only after annealing at 900 °C. The failure is induced by a premature crystallization of the Ta₃₆Si₁₄N₅₀ alloy (whose crystallization temperature exceeds 1000 °C) when in contact with copper.