Amorphous Ta-Si-N diffusion barriers in Si/Al and Si/Cu metallizations

Thin films of amorphous Ta-Si-N alloys were deposited by reactive RF sputtering of a Ta₅Si₃ target in an Ar/N₂ ambient. These alloy films were tested as diffusion barriers between Al and Si, as well as between Cu and Si. Electrical measurements on Schottky diodes and on shallow n⁺p junction diodes were used to evaluate the thermal stability of the 〈Si〉 /W₄₈Si₂₀N₃₂(20 nm)/Ta₃₆Si₁₄N₅₀(80 nm)/Al(1000 nm) metallization. The amorphous W₄₈Si₂₀N₃₂ contacting layer was added to raise the Schottky barrier height of the metallization on n-type Si. Both the shallow junctions and the Schottky diodes are stable up to 700°C for 20 min (above the Al melting point of 660°C) which makes this material the best thin-film diffusion barrier on record. Furthermore, the same Ta₃₆Si₁₄N₅₀ amorphous film maintains the integrity of the I-V characteristics of the shallow n⁺p junctions with the 〈Si〉 /TiSi₂(30 nm)/Ta₃₆Si₃₄N₅₀(80 nm)/Cu(500 nm) metallization up to 900°C for 30 min annealing in vacuum. The TiSi₂ contacting layer was added to assure an ohmic characteristic of the contact. For comparison, the same shallow junctions with 〈Si〉 /Cu metallizations were shorted after annealing at 300°C.