Interfacial Diffusion Studies of Cu/(5 nm Ru)/Si Structures Physical Vapor Deposited vs Electrochemically Deposited Cu

In contrast to physical vapor deposition (PVD), the electrochemical deposition (ECD) process is dependent upon substrate resistivity. ECD of Cu on ultrathin Ru diffusion barriers remains a technological challenge due to large resistivity increase over a wide plating area. Results are presented from the comparative investigation of interfacial stability and Cu diffusion processes in PVD and ECD Cu/(5 nm Ru)/Si structures. Cu can be conformally electroplated onto (5 nm Ru)/Si surfaces (ca. 1 cm2) with over 94% efficiency. However, lesser uniformity and conformality of ECD Cu are observed on (5 nm Ru)/Si samples with larger surface areas. The transmission electron microscopy (TEM) reveals that ECD Cu film is less densely packed (ca. 70 nm) than PVD Cu. HRTEM studies in conjunction with surface analyses using optical microscopy and four-point probe resistivity measurements show that 5 nm Ru can successfully impede Cu diffusion up to 300DGC for 10 min, but fails at 450DGC. Interfacial profiling data obtained from back side secondary-ion mass spectrometry (SIMS) analysis agree with TEM results. X-ray photoelectron spectroscopy (XPS) investigation on nitric acid-etched PVD and ECD Cu/(5 and 20 nm Ru)/Si samples shows the presence of residual ECD Cu after annealing, suggesting that ECD Cu diffuses further into Ru than PVD Cu.