EFFECT OF UNDERLAYERS ON THE STRESS OF CU FILMS PREPARED USING IONIZED METAL PLASMA

We investigated the effect of barrier metals, Ta, TaN and multi-stacked Ta/TaN, on the stress of the late deposited Cu film using ionised-metal plasma (IMP) technique. It was found that the stress of the IMP Cu film is sensitive to the strain or lattice mismatch of the barrier layer underneath. The nitrogen composition incorporated into Ta barrier layer causes tensile strain in the barrier and also the stress in the late deposited Cu film. The Cu film deposited on a multi-stacked Ta/TaN barrier showed the smallest stress due to relaxation of strain in the multi-layer barrier. In addition, the stress was also found sensitive to the annealing temperature. The abrupt change in the stress at high annealing temperatures coincides well with the formation of Cu3Si compound.