We have studied sputter-deposited Ta, Ta s6 't4, and Ta3&ir4N~e thin lilms as diffusion Sr 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)/Ta7$iZ6(100 nm)/ Cu(500 nm) metallization to 650 "C!. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta3,&N5c(120 nm)/Cu(500 nm) and in the Si/TiSi2(30 nm)/Ta3,$iNS0(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 Ta3&&, alloy (whose crystallization temperature exceeds 1000 "C) when in contact with copper.

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The oxidation behavior of reactively sputtered amorphous tungsten nitride of composition W 80 N 20 was investigated in dry and wet oxidizing ambient in the temperature range of 450 ·c-575 ·c. A single W0 3 oxide phase is observed. The growth of the oxide follows a parabolic time dependence which is attributed to a process controlled by the diffusivity of the oxidant in the oxide. The oxidation process is thermally activated with an activation energy of 2.5 ±0.05 eV for dry ambient and 2.35 ±0.05 eV for wet ambient. The pre-exponential factor of the reaction constant for dry ambient is 1.1 X 10 21 A 2 /min; that for wet ambient is only about lO times less and is equal to 1.3 X 10 20 A 2 /min.

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