Ta/Cu is a strategic material combination for ultra-large-scale integrated wafer technology. Here we report an unconventional method for the synthesis of a [110]-oriented nanocrystalline R-Ta thin film on freshly prepared Cu(111) templates at <50 °C without any redundant underlayers and post-growth treatments. The crystallite size of the R-Ta-containing thin film is in the range of only 6-8 nm, and the Ta film resistivity is reduced significantly from 186 µΩ cm down to 104 µΩ cm with this novel method.

Copper shows a tendency to drift into contiguous dielectric material under bias and temperature stressing. The stability of different compositions ͑by changing silane gas flow rate͒ of Ti-Si-N-O films has been investigated using metal-oxide-semiconductor ͑MOS͒ capacitors. MOS samples preannealed at 250°C and subjected to bias temperature stressing ͑BTS͒ at 150°C, 200°C under an electrical field of 0.5 or 1 MV/cm show stable capacitance-voltage behavior with no flatband voltage shift from as-annealed to 90 min of BTS for Ti-Si-N-O film with Si/Ti ratio of 0.48. The lack of flatband voltage shift indicates that Ti-Si-N-O film is able to prevent Cu ion penetration. It is found that the electrical stability of Ti-Si-N-O film is reduced with higher Si/Ti ratio. For Ti-Si-N-O film with Si/Ti ratio of 0.91, flatband voltage shifts 0.75 V after 90 min of BTS at 150°C and 0.5 MV/cm, and this shift is attributed to the interface states at the Ti-Si-N-O/oxide interface that were generated during the plasma process and could not be fully healed after 250°C annealing. Thus, it is suggested that with low silane gas flow rate, an electrically stable Ti-Si-N-O film can be achieved with fewer interface states.The implementation of copper in back-end-of-line metallization yields advantages such as low electrical resistivity, superior resistance to electromigration, and faster signal speed. However, copper in comparison to aluminum has a higher tendency to drift into interlevel dielectric as well as into the silicon substrate in the presence of an electrical field even at low temperature, 1-4 resulting in a degradation of the electrical properties. Thus, a barrier layer is required between Cu/dielectric for reliable integration.Various refractory metals and their nitrides have been heavily examined as barrier materials. For example, TaN has been recognized as one of the most promising diffusion barriers for copper due to its high thermal stability, chemical inactivity with Cu, 5,6 and no intermetallic formation at elevated temperatures. 5 Besides TaN, extensive work in the deposition of TiN by both sputtering 7,8 and chemical vapor deposition 9,10 has been reported. A common denominator underlying many of the above references is the columnar structure of TiN, typically with a ͑111͒ or ͑200͒ preferred orientation. Such a structure can lead to short-circuit diffusion paths via grain boundaries and result in the failure of the devices. With the downscaling of devices and more stringent reliability requirements, there is a need for more effective barrier materials. To this end, a class of refractory ternary nitrides, such as Ti-Si-N, Ta-Si-N, and W-Si-N, has been proposed as candidates for the next-generation diffusion barrier in copper/low-k dielectric back-end-of-line device fabrication. 11,12 Various research groups have explored the formation of ternary nitride films by physical vapor deposition ͑PVD͒, metallorganic chemical vapor deposition, and metallorganic atomic layer deposition techniques, documenting their resulting electric...

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Different processes, including ''cool'' physical vapor deposition ͑PVD͒, of Ta barrier and Cu seed deposition were compared in Cu interconnect development. In the cool Ta process, the substrate temperature was Ͻ50°C, compared to a temperature of about Ͼ100°C in the standard process. With the cool process, via resistance ͑0.19 m in via size͒ was reduced by about 25%, although 40% thicker Ta was measured at the via bottom. This was not in agreement with the common understanding that the thicker the Ta film is, the higher the via resistance. Blank film studies suggested that a mixed texture of ␣and ␤-Ta was formed at via bottom in the new Ta/Cu process. X-ray diffraction spectra clearly exhibited the existence of ␣-Ta in addition to the ␤-Ta, where the latter is usually observed in the standard process. Electron diffraction spectra further supported the claim of mixed ␣-/␤-Ta formation at via bottom. Moreover, Rutherford backscattering data suggested that the mixed ␣-/␤-Ta had even higher thermal stability.