Tiruchirapalli Arunagiri

Electrodeposition of Copper Thin Film on Ruthenium A Potential Diffusion Barrier for Cu Interconnects

The electrochemical deposition of copper (Cu) thin film on polycrystalline ruthenium (Ru) electrode surface was investigated in a sulfuric acid plating bath. Scanning electron microscopic characterization indicated that a continuous thin Cu film (150 A and above) could be conformally coated on Ru with good control of thickness. The nucleation and growth of Cu on Ru was studied using the potentiostatic current-transient method. The results support a predominantly progressive nucleation of Cu on the Ru surface. In addition, X-ray diffraction patterns indicated (i) a principally (111) texture of the electrochemically grown Cu on Ru and (ii) the absence of any new phase or compound formation between the two metals, even after annealing up to 800°C. Scotch tape peel tests showed that Cu films adhered strongly to Ru, both before and after the annealing treatments. The lack of metallurgical interaction and strong adhesion between Cu and Ru at elevated temperatures underscore the potential application of Ru as a new Cu diffusion barrier.

Diffusion studies of copper on ruthenium thin film a plateable copper diffusion barrier

Diffusion studies were carried out on physical vapor deposited Cu/Ru(∼20 nm)/Si samples using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Back side SIMS depth profiling revealed well-defined interfaces and showed that Cu interdiffusion was impeded by Ru thin film up to 450°C vacuum annealing. TEM showed a 20-22 nm Ru barrier layer with a columnar microstructure oriented vertically with respect to Si substrate. TEM results corroborate with SIMS data to indicate stability of the Ru film barrier for annealing temperatures up to 450°C. Direct Cu electroplating on ultrathin Ru barrier layers (<20 nm) was investigated in sulfuric acid. The electroplated Cu film is shiny, smooth, and without agglomeration under scanning electron microscopy. Excellent adhesion between interfacial layers was confirmed by the scribe-peel test. The interfacial characterization results indicate that Ru thin film is a promising candidate as a directly plateable Cu diffusion barrier.

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 cm 2 ) 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 300°C for 10 min, but fails at 450°C. 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.

Underpotential Deposition of Copper on Electrochemically Prepared Conductive Ruthenium Oxide Surface

Copper underpotential deposition (UPD) on a conductive hydrous ruthenium oxide (RuO x H y ) surface was studied by progressive cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Cu UPD on an electrochemically prepared RuO x H y surface started at 0.15 V in a 2 mM CuSO 4 solution and reached a coverage plateau of ca. 0.9 monolayer (ML) beyond -0.05 V (vs. Ag/AgCl). XPS data confirmed that Cu deposits underpotentially on RuO x H y surface. The anodic polarization potential determines the chemical states and affects the Cu UPD/bulk deposition of RuO x H y electrode. We observed close to a 55% increase of underpotential shift for Cu UPD on RuO x H y (ca. 170 mV) in comparison to Ru surface (ca. 110 mV). The results suggest that interfacial binding of the first ML of Cu on RuO x H y is stronger than Ru by 12 kJ mol - 1 . Possible applications of Cu UPD to Ru-based plateable seedless Cu diffusion barrier are discussed.