Barrier and seed repair performance of thin RuTa films for Cu interconnects

Thin (<4 nm) Physical Vapor Deposited (PVD) Ru-10 at.% Ta films were evaluated as diffusion barriers and seed enhancement layers for Cu metallization in sub 25 nm trenches. The ratio of Ru/Ta on blanket wafers could be influenced by changing the process conditions. However, a difference in Ru/Ta ratio did not influence the thermal stability of the layers during High Temperature X-ray Diffraction (HT-XRD) measurements as all RuTa films exhibited good thermal properties since no Cu-silicide formation was observed for temperatures below 500 °C. The RuTa films also passed an 85 °C/85% relative humidity (RH) test of one week of storage in order to test the H₂O barrier integrity of the films. Furthermore no difference was found when testing the O₂ barrier integrity during 300 s anneals at various temperatures between 250 °C and 500 °C. Good Cu fill of 20 nm trenches (AR 4:1) patterned in oxide was achieved when combining the RuTa films with PVD Cu seed layers with thicknesses ranging from 7 to 20 nm and Cu plating. When compared to a Ta(N)/Ta barrier, relatively high electrical yields (60-80%) were obtained for structures with CDs <30 nm when combining RuTa films with PVD Cu seed layers as thin as 7 nm (on field), hence evidencing the seed enhancement ability of these layers.