Failure mechanisms of PVD Ta and ALD TaN barrier layers for Cu contact applications
PVD Ta-based and ALD TaN layers were studied as Cu diffusion barriers on poly-silicon, NiSi and CoSi2 for Cu contact applications. The effectiveness of nanometer-thick layers, deposited in manufacturing compatible chambers on 200 and 300mm wafers, is evaluated by detection of Cu-silicidation temperature using high temperature in situ XRD. It is found that Si diffuses into the ?-Ta lattice for PVD barriers between 300 and 500C, and induces Ta silicidation at 600C. The agglomeration of TaSi2 seems to be responsible for the damage of barrier continuity and cause subsequent Cu-silicidation. The growth of ALD TaN on different surfaces of NiSi was studied by XRF, RBS and XRR. The growth curves show excellent linearity as a function of thickness. TOF-SIMS shows closed layers after 60 ALD cycles. In situ XRD reveals that the failure temperature of 4nm thick ALD layers is higher than 500C. It is found that the failure of 3 and 4nm ALD TaN layers in Cu/barrier/NiSi stacks is a diffusion controlled process, with an activation energy Q of ?2.2eV and a pre-exponential factor D0 of ?3.810?3cm2/s.
pvd ta ald tan cu contacts cu diffusion barrier backend interconnects