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-degrees-C. An amorphous Ta74Si26 thin film improves the performance by raising the failure temperature of a <Si>/Ta74Si26(100 nm)/Cu(500 nm) metallization to 650-degrees-C. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta36Si14N50 (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-degrees-C. The failure is induced by a premature crystallization of the Ta36Si14N50 alloy (whose crystallization temperature exceeds 1000-degrees-C) when in contact with copper.