Interfacial Diffusion Studies of Cu∕(5 nm Ru)∕Si Structures

Abstract

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∕(50.3emnm0.3emnormalRu)∕Si structures. Cu can be conformally electroplated onto (50.3emnm0.3emnormalRu)∕Si surfaces (ca. 1cm2 ) with over 94% efficiency. However, lesser uniformity and conformality of ECD Cu are observed on (50.3emnm0.3emnormalRu)∕Si samples with larger surface areas. The transmission electron microscopy (TEM) reveals that ECD Cu film is less densely packed (ca. 70nm ) than PVD Cu. HRTEM studies in conjunction with surface analyses using optical microscopy and four-point probe resistivity measurements show that 5nm Ru can successfully impede Cu diffusion up to 300°C for 10min , 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∕(50.3emand0.3em200.3emnm0.3emnormalRu)∕Si samples shows the presence of residual ECD Cu after annealing, suggesting that ECD Cu diffuses further into Ru than PVD Cu.

5 nm Amorphous Boron and Carbon Added Ru Film as a Highly Reliable Cu Diffusion Barrier

“…This result is consistent with previous articles that a failure Cu/Ru/Si structure is induced by the formation of a less dense Ru 2 Si 3 interfacial layer. 12,15,24 The columnlike ruthenium silicide layer promotes Cu diffusion, causing massive Cu reactions with Si. 13 In comparison, the Ru-B-C layer was superior to Ru in preventing Cu diffusion.…”

“…2a͒ at 600°C indicate that Ru 2 Si 3 forms before Cu silicide. Other articles 12,15,24 have also indicated that the failure mechanism of a Cu/Ru/Si structure is related to Ru 2 Si 3 crystallite formation, which forms a discontinuous and less dense interlayer and causes massive Cu diffusion through these rapid diffusion paths. 13 In contrast, the GIXRD patterns in Fig.…”

“…A 20 nm Ru barrier can prevent Cu diffusion up to 450°C for 10 min, 11 whereas a 5 nm Ru film is only stable at 300°C for 10 min. 12,15 Recent studies of phosphorus-added Ru film demonstrated that 12 nm Ru͑P͒ can effectively block Cu diffusion above 700°C for 5 min, 16 and a separate study showed a similar effect at 300°C for 67 h. 17 This superior performance is attributed to the amorphous microstructure that results when phosphorus is added. A 15 nm Ru-Ta layer effectively blocked Cu diffusion up to 600°C for 30 min.…”

The oxide electrochemistry of ruthenium and its relevance to trench liner applications in damascene copper plating

“…There is considerable interest at the present time [1][2][3][4][5][6][7][8][9][10][11][12][13] in the possible use of ruthenium as an ultrathin trench liner in damascene copper plating which is currently employed in the microelectronics area for the production of on-chip interconnects. The advantages of ruthenium as a trench liner are that ideally it prevents copper transport from the filled trench into the silicon (thus averting device degradation), it is directly platable (dispensing with the need for a seed layer) and it provides strong adhesion between the electrodeposited copper and the barrier film (which reduces copper electromigration at the Ru/Cu interface).…”

Direct Cu Electrodeposition on Ta Using Pd Nanocolloids: Effect of Allyl Alcohol on the Formation of Seed Layer

“…[1][2][3] Among these steps, the diffusion barrier and Cu seed layer are formed by physical vapor deposition (PVD). Generally, metals deposited by the PVD method show good adhesion with the substrate and superior film properties, such as low resistivity and low surface roughness.…”