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

Abstract

The failure mode and Cu barrier properties of a 5 nm thick boron and carbon added Ru ͑Ru-B-C͒ film deposited on Si substrate have been investigated. Results from X-ray diffraction ͑XRD͒ and Fourier-transformed electron diffraction patterns indicate that the Ru-B-C film is amorphous up to 700°C. Unlike pure Ru film, the Ru in the Ru-B-C film recrystallized at 750°C instead of reacting with Si at the interface to form Ru 2 Si 3 . The sheet resistance and XRD results show that the 5 nm Ru-B-C barrier is thermally stable up to 750°C, whereas the 5 and 10 nm Ru are only stable below 550 and 600°C, respectively.Copper and porous ultralow-k ͑p-ULK͒ interconnects have been implemented in advanced integrated circuits ͑ICs͒ to reduce resistive-capacitive ͑RC͒ delay. 1,2 However, Cu can easily diffuse in porous materials. This deep-level trap can also propagate in silicon, which deteriorates device performance. 3-7 A highly reliable Cu barrier is required.The traditional Ta/TaN bilayer barrier has been widely adopted for IC production. Unfortunately, ever-decreasing feature sizes also create a demand for scaling of the copper barrier thickness. However, when barrier thickness is reduced to 1.7 nm for the 22 nm node technology, 8 the resistance of Ta/TaN films cannot meet the requirements of the International Technology Roadmap for Semiconductors. Furthermore, a reduced barrier cannot provide continuous film coverage on the rough sidewalls of p-ULK film in dual damascene structures. A barrier that is capable of Cu plating without a Cu seed layer allows a slightly thicker film ͑which is equal to the combined thickness of barrier and Cu seed layers͒ and is a promising approach to solve the above issues. Directly platable metals 9 include Ru, Pd, Pt, Rh, and Ir. Of these metals, Ru has a low resistance and is immiscible with Cu, 10 thus attracting much interest for use as a directly platable Cu barrier.However, pure Ru film exhibits poor performance as a Cu diffusion barrier due to its columnar microstructure, 11-14 which provides rapid diffusion paths for Cu atoms. 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. 18 A plasma-enhanced atomic layer deposited 10 nm amorphous Ru 0.58 -͑TiN͒ 0.42 film was stable at 700°C over a 30 min anneal. 19 Ternary alloys tend to have higher recrystallization temperatures because grain nucleation is delayed by an added third element. 20,21 To our knowledge, an ultrathin ͑ϳ5 nm͒ robust Ru-based seedless barrier deposited on Si substrate, which is more sensitive to sheet resistance value, has not yet been reported.In this articl...

Recent Advances in Barrier Layer of Cu Interconnects

“…Many studies [118][119][120][121][122][123][124] have demonstrated that some foreign elements, such as boron (B), phosphorus (P) and carbon (C) are able to induce the formation of amorphous Ru thin films and thereby significantly improve the ability of Ru thin films to prevent Cu interdiffusion. A 12 nm thin film of Ru (P) deposited on a low-κ dielectric layer effectively prevented the diffusion of Cu into Si wafer at 800 • C for 5 min [124].…”

“…A 12 nm thin film of Ru (P) deposited on a low-κ dielectric layer effectively prevented the diffusion of Cu into Si wafer at 800 • C for 5 min [124]. Perng et al [123] proved that the temperature of forming an amorphous phase of a 5 nm thin film of Ru-B-C was significantly higher than that of pure Ru under thermal annealing and the doped film was thermally stable up to 750 • C. Metal elements can also be applied as dopant to form an amorphous structure with Ru and increase its thermal stability. Chen et al [125] showed that a 15 nm amorphous Ru-Ta thin film was able to resist Cu interdiffusion at 700 • C for 30 min.…”

New Copper Alloy, Cu(SnNx), Films Suitable for More Thermally Stable, Electrically Reliable Interconnects and Lower-Leakage Current Capacitors

“…When forming a Cu interconnect atop a silicon (Si) substrate, we need to introduce a diffusion-barrier layer between the two to prevent any detrimental interaction occurring between the copper interconnect and the silicon substrate. 1,2) However, miniaturizing such interconnect-related devices seems to be challenging. The main weakness of such a technique is that Cu is prone to react with silicon at low temperatures ($200 C), hence and throughout causing device failure.…”