Fusen Chen

Oxidation of Ta diffusion barrier layer for Cu metallization in thermal annealing

Abstract This work examines the thermal stability of Ta barrier layer for Cu metallization with the effect of oxygen. The Cu/Ta/SiO 2 /Si films were annealed at temperatures ranging from 400 to 600°C under various vacuum conditions. Transmission electron microscopy has been performed to characterize the microstructure of the films after annealing. The results show that an amorphous interlayer of oxide between Cu and Ta can be formed at 400°C in a vacuum of 10 −2 mbar. X-Ray energy dispersive spectroscopy and electron energy loss spectroscopy confirm that this interlayer is tantalum oxide. This interlayer transformed into a crystalline phase of Ta–Cu oxide at 600°C. In addition, formation of tantalum oxide interlayer is more thermodynamically favorable than that of copper oxide layer at the Cu/Ta interface. Growth of the amorphous interlayer is atmosphere-dependent, as evidenced by the thickness of tantalum oxide being decreased with better vacuum or argon gas. This observation suggests that the oxidation source may arise from the annealing atmosphere rather than from interior SiO 2 . Furthermore, it has been observed that oxygen diffuses along grain boundaries in copper films to cause tantalum oxidation.

Deposition of copper by using self-sputtering

A magnetron sputtering source using sustained self-sputtering has been developed for uniform deposition of copper on large wafers (200 mm in diameter). Usually, Ar gas is used in sputter deposition. In sustained self-sputtering, no Ar gas was used for deposition, the sputtered Cu atoms were ionized in the magnetron plasma, and some Cu ions were accelerated to sputter more Cu atoms out of the target. In this work, the magnetron was optimized to allow sustained self-sputter deposition of Cu on 200 mm wafers with reasonable power (9–12 kW). When sputtering a target of 325 mm in diameter, the minimum power density to sustain plasma without using Ar gas was found to be 10.8 W/cm2. This was much lower than the threshold power density reported in the literature. A chamber employing a large spacing between the target and wafer (16 cm) was used. The resulting deposition rate was about 320 nm/min, when a 12 kW of dc power was applied. The standard deviation in film thickness was less than 2.5% in our limited experi...

The effect of oxygen in the annealing ambient on interfacial reactions of Cu/Ta/Si multilayers

Abstract Interfacial reactions of Cu/Ta/Si multilayers after thermal treatment were investigated using transmission electron microscopy. The Cu and Ta films were deposited onto Si wafer by ionized metal plasma technique. The samples were then annealed at 400, 500, 550 and 600°C in purified Ar atmosphere for 30 min. The effect of oxygen in the atmosphere on the thermal stability is studied. An interlayer of Ta oxide was observed between Cu and Ta after annealing at 400, 500 and 550°C. It is evident that oxygen as residual gas from furnace ambient can diffuse through Cu grain boundaries to form the Ta oxide layer. After annealing at 600°C, Si reacted with Ta to form TaSi 2 at the interface of Ta and Si, in the meantime Cu 3 Si with surrounding SiO 2 formed in the Si substrate. The thermal stability of the Cu/Ta/Si samples was also examined in a two-step annealing treatment of 400°C for 30 min, followed by 600°C for 30 min. Even though interlayers of crystalline Ta–Cu oxide and Ta silicide were formed, Cu silicides were not observed. Formation of TaO x interlayer at the first stage of 400°C annealing may inhibit Cu diffusion into the Si substrate in the second stage of the 600°C annealing process.

Advanced Cu barrier/seed development for 65nm technology and beyond

A novel PVD sputtering source has been developed based on a high power-density concept. The new sputtering source dramatically increases the metal ion traction which improves TaN/Ta barrier and Cu seed step coverage and gap fill capability in Cu metallization. Successful ECP gap fill has been achieved on the most aggressive features currently available - 0.08/spl mu/m 6:1 aspect ratio vias - when a 300/spl Aring/ Cu seed layer is deposited with this new source. Electrical test results based on the testing structure of 90nm technology node including parametric and stress migration, are equivalent or better than current processes. The new source will further extend the lifetime of PVD in the IC industry.